TurboJPEG: TurboJPEG

TurboJPEG 2.1.4

Data Structures | Macros | Typedefs | Enumerations | Functions | Variables
TurboJPEG

TurboJPEG API. More...

## Data Structures
struct | tjscalingfactor
| Scaling factor. More...
struct | tjregion
| Cropping region. More...
struct | tjtransform
| Lossless transform. More...

## Macros
#define | TJ_NUMSAMP
| The number of chrominance subsampling options. More...
#define | TJ_NUMPF
| The number of pixel formats. More...
#define | TJ_NUMCS
| The number of JPEG colorspaces. More...
#define | TJFLAG_BOTTOMUP
| Rows in the packed-pixel source/destination image are stored in bottom-up (Windows, OpenGL) order rather than in top-down (X11) order. More...
#define | TJFLAG_FASTUPSAMPLE
| When decompressing an image that was compressed using chrominance subsampling, use the fastest chrominance upsampling algorithm available. More...
#define | TJFLAG_NOREALLOC
| Disable JPEG buffer (re)allocation. More...
#define | TJFLAG_FASTDCT
| Use the fastest DCT/IDCT algorithm available. More...
#define | TJFLAG_ACCURATEDCT
| Use the most accurate DCT/IDCT algorithm available. More...
#define | TJFLAG_STOPONWARNING
| Immediately discontinue the current compression/decompression/transform operation if a warning (non-fatal error) occurs. More...
#define | TJFLAG_PROGRESSIVE
| Use progressive entropy coding in JPEG images generated by the compression and transform functions. More...
#define | TJFLAG_LIMITSCANS
| Limit the number of progressive JPEG scans that the decompression and transform functions will process. More...
#define | TJ_NUMERR
| The number of error codes. More...
#define | TJ_NUMXOP
| The number of transform operations. More...
#define | TJXOPT_PERFECT
| This option will cause tjTransform() to return an error if the transform is not perfect. More...
#define | TJXOPT_TRIM
| This option will cause tjTransform() to discard any partial MCU blocks that cannot be transformed. More...
#define | TJXOPT_CROP
| This option will enable lossless cropping. More...
#define | TJXOPT_GRAY
| This option will discard the color data in the source image and produce a grayscale destination image. More...
#define | TJXOPT_NOOUTPUT
| This option will prevent tjTransform() from outputting a JPEG image for this particular transform. More...
#define | TJXOPT_PROGRESSIVE
| This option will enable progressive entropy coding in the JPEG image generated by this particular transform. More...
#define | TJXOPT_COPYNONE
| This option will prevent tjTransform() from copying any extra markers (including EXIF and ICC profile data) from the source image to the destination image. More...
#define | TJPAD(width)
| Pad the given width to the nearest multiple of 4. More...
#define | TJSCALED(dimension, scalingFactor)
| Compute the scaled value of `dimension` using the given scaling factor. More...

## Typedefs
typedef struct tjtransform | tjtransform
| Lossless transform. More...
typedef void * | tjhandle
| TurboJPEG instance handle. More...

## Enumerations
enum | TJSAMP { TJSAMP_444, TJSAMP_422, TJSAMP_420, TJSAMP_GRAY, TJSAMP_440, TJSAMP_411 }
| Chrominance subsampling options. More...
enum | TJPF { TJPF_RGB, TJPF_BGR, TJPF_RGBX, TJPF_BGRX, TJPF_XBGR, TJPF_XRGB, TJPF_GRAY, TJPF_RGBA, TJPF_BGRA, TJPF_ABGR, TJPF_ARGB, TJPF_CMYK, TJPF_UNKNOWN }
| Pixel formats. More...
enum | TJCS { TJCS_RGB, TJCS_YCbCr, TJCS_GRAY, TJCS_CMYK, TJCS_YCCK }
| JPEG colorspaces. More...
enum | TJERR { TJERR_WARNING, TJERR_FATAL }
| Error codes. More...
enum | TJXOP { TJXOP_NONE, TJXOP_HFLIP, TJXOP_VFLIP, TJXOP_TRANSPOSE, TJXOP_TRANSVERSE, TJXOP_ROT90, TJXOP_ROT180, TJXOP_ROT270 }
| Transform operations for tjTransform() More...

## Functions
DLLEXPORT tjhandle | tjInitCompress (void)
| Create a TurboJPEG compressor instance. More...
DLLEXPORT int | tjCompress2 (tjhandle handle, const unsigned char *srcBuf, int width, int pitch, int height, int pixelFormat, unsigned char **jpegBuf, unsigned long *jpegSize, int jpegSubsamp, int jpegQual, int flags)
| Compress a packed-pixel RGB, grayscale, or CMYK image into a JPEG image. More...
DLLEXPORT int | tjCompressFromYUV (tjhandle handle, const unsigned char *srcBuf, int width, int align, int height, int subsamp, unsigned char **jpegBuf, unsigned long *jpegSize, int jpegQual, int flags)
| Compress a unified planar YUV image into a JPEG image. More...
DLLEXPORT int | tjCompressFromYUVPlanes (tjhandle handle, const unsigned char **srcPlanes, int width, const int *strides, int height, int subsamp, unsigned char **jpegBuf, unsigned long *jpegSize, int jpegQual, int flags)
| Compress a set of Y, U (Cb), and V (Cr) image planes into a JPEG image. More...
DLLEXPORT unsigned long | tjBufSize (int width, int height, int jpegSubsamp)
| The maximum size of the buffer (in bytes) required to hold a JPEG image with the given parameters. More...
DLLEXPORT unsigned long | tjBufSizeYUV2 (int width, int align, int height, int subsamp)
| The size of the buffer (in bytes) required to hold a unified planar YUV image with the given parameters. More...
DLLEXPORT unsigned long | tjPlaneSizeYUV (int componentID, int width, int stride, int height, int subsamp)
| The size of the buffer (in bytes) required to hold a YUV image plane with the given parameters. More...
DLLEXPORT int | tjPlaneWidth (int componentID, int width, int subsamp)
| The plane width of a YUV image plane with the given parameters. More...
DLLEXPORT int | tjPlaneHeight (int componentID, int height, int subsamp)
| The plane height of a YUV image plane with the given parameters. More...
DLLEXPORT int | tjEncodeYUV3 (tjhandle handle, const unsigned char *srcBuf, int width, int pitch, int height, int pixelFormat, unsigned char *dstBuf, int align, int subsamp, int flags)
| Encode a packed-pixel RGB or grayscale image into a unified planar YUV image. More...
DLLEXPORT int | tjEncodeYUVPlanes (tjhandle handle, const unsigned char *srcBuf, int width, int pitch, int height, int pixelFormat, unsigned char **dstPlanes, int *strides, int subsamp, int flags)
| Encode a packed-pixel RGB or grayscale image into separate Y, U (Cb), and V (Cr) image planes. More...
DLLEXPORT tjhandle | tjInitDecompress (void)
| Create a TurboJPEG decompressor instance. More...
DLLEXPORT int | tjDecompressHeader3 (tjhandle handle, const unsigned char *jpegBuf, unsigned long jpegSize, int *width, int *height, int *jpegSubsamp, int *jpegColorspace)
| Retrieve information about a JPEG image without decompressing it, or prime the decompressor with quantization and Huffman tables. More...
DLLEXPORT tjscalingfactor * | tjGetScalingFactors (int *numScalingFactors)
| Returns a list of fractional scaling factors that the JPEG decompressor supports. More...
DLLEXPORT int | tjDecompress2 (tjhandle handle, const unsigned char *jpegBuf, unsigned long jpegSize, unsigned char *dstBuf, int width, int pitch, int height, int pixelFormat, int flags)
| Decompress a JPEG image into a packed-pixel RGB, grayscale, or CMYK image. More...
DLLEXPORT int | tjDecompressToYUV2 (tjhandle handle, const unsigned char *jpegBuf, unsigned long jpegSize, unsigned char *dstBuf, int width, int align, int height, int flags)
| Decompress a JPEG image into a unified planar YUV image. More...
DLLEXPORT int | tjDecompressToYUVPlanes (tjhandle handle, const unsigned char *jpegBuf, unsigned long jpegSize, unsigned char **dstPlanes, int width, int *strides, int height, int flags)
| Decompress a JPEG image into separate Y, U (Cb), and V (Cr) image planes. More...
DLLEXPORT int | tjDecodeYUV (tjhandle handle, const unsigned char *srcBuf, int align, int subsamp, unsigned char *dstBuf, int width, int pitch, int height, int pixelFormat, int flags)
| Decode a unified planar YUV image into a packed-pixel RGB or grayscale image. More...
DLLEXPORT int | tjDecodeYUVPlanes (tjhandle handle, const unsigned char **srcPlanes, const int *strides, int subsamp, unsigned char *dstBuf, int width, int pitch, int height, int pixelFormat, int flags)
| Decode a set of Y, U (Cb), and V (Cr) image planes into a packed-pixel RGB or grayscale image. More...
DLLEXPORT tjhandle | tjInitTransform (void)
| Create a new TurboJPEG transformer instance. More...
DLLEXPORT int | tjTransform (tjhandle handle, const unsigned char *jpegBuf, unsigned long jpegSize, int n, unsigned char **dstBufs, unsigned long *dstSizes, tjtransform *transforms, int flags)
| Losslessly transform a JPEG image into another JPEG image. More...
DLLEXPORT int | tjDestroy (tjhandle handle)
| Destroy a TurboJPEG compressor, decompressor, or transformer instance. More...
DLLEXPORT unsigned char * | tjAlloc (int bytes)
| Allocate a byte buffer for use with TurboJPEG. More...
DLLEXPORT unsigned char * | tjLoadImage (const char *filename, int *width, int align, int *height, int *pixelFormat, int flags)
| Load a packed-pixel image from disk into memory. More...
DLLEXPORT int | tjSaveImage (const char *filename, unsigned char *buffer, int width, int pitch, int height, int pixelFormat, int flags)
| Save a packed-pixel image from memory to disk. More...
DLLEXPORT void | tjFree (unsigned char *buffer)
| Free a byte buffer previously allocated by TurboJPEG. More...
DLLEXPORT char * | tjGetErrorStr2 (tjhandle handle)
| Returns a descriptive error message explaining why the last command failed. More...
DLLEXPORT int | tjGetErrorCode (tjhandle handle)
| Returns a code indicating the severity of the last error. More...

## Variables
static const int | tjMCUWidth [TJ_NUMSAMP]
| MCU block width (in pixels) for a given level of chrominance subsampling. More...
static const int | tjMCUHeight [TJ_NUMSAMP]
| MCU block height (in pixels) for a given level of chrominance subsampling. More...
static const int | tjRedOffset [TJ_NUMPF]
| Red offset (in bytes) for a given pixel format. More...
static const int | tjGreenOffset [TJ_NUMPF]
| Green offset (in bytes) for a given pixel format. More...
static const int | tjBlueOffset [TJ_NUMPF]
| Blue offset (in bytes) for a given pixel format. More...
static const int | tjAlphaOffset [TJ_NUMPF]
| Alpha offset (in bytes) for a given pixel format. More...
static const int | tjPixelSize [TJ_NUMPF]
| Pixel size (in bytes) for a given pixel format. More...

## Detailed Description

TurboJPEG API.

This API provides an interface for generating, decoding, and transforming planar YUV and JPEG images in memory.

## YUV Image Format Notes

Technically, the JPEG format uses the YCbCr colorspace (which is technically not a colorspace but a color transform), but per the convention of the digital video community, the TurboJPEG API uses "YUV" to refer to an image format consisting of Y, Cb, and Cr image planes.

Each plane is simply a 2D array of bytes, each byte representing the value of one of the components (Y, Cb, or Cr) at a particular location in the image. The width and height of each plane are determined by the image width, height, and level of chrominance subsampling. The luminance plane width is the image width padded to the nearest multiple of the horizontal subsampling factor (1 in the case of 4:4:4, grayscale, or 4:4:0; 2 in the case of 4:2:2 or 4:2:0; 4 in the case of 4:1:1.) Similarly, the luminance plane height is the image height padded to the nearest multiple of the vertical subsampling factor (1 in the case of 4:4:4, 4:2:2, grayscale, or 4:1:1; 2 in the case of 4:2:0 or 4:4:0.) This is irrespective of any additional padding that may be specified as an argument to the various YUV functions. The chrominance plane width is equal to the luminance plane width divided by the horizontal subsampling factor, and the chrominance plane height is equal to the luminance plane height divided by the vertical subsampling factor.

For example, if the source image is 35 x 35 pixels and 4:2:2 subsampling is used, then the luminance plane would be 36 x 35 bytes, and each of the chrominance planes would be 18 x 35 bytes. If you specify a row alignment of 4 bytes on top of this, then the luminance plane would be 36 x 35 bytes, and each of the chrominance planes would be 20 x 35 bytes.

## Macro Definition Documentation

## ◆ TJ_NUMCS

#define TJ_NUMCS

The number of JPEG colorspaces.

## ◆ TJ_NUMERR

#define TJ_NUMERR

The number of error codes.

## ◆ TJ_NUMPF

#define TJ_NUMPF

The number of pixel formats.

## ◆ TJ_NUMSAMP

#define TJ_NUMSAMP

The number of chrominance subsampling options.

## ◆ TJ_NUMXOP

#define TJ_NUMXOP

The number of transform operations.

## ◆ TJFLAG_ACCURATEDCT

#define TJFLAG_ACCURATEDCT

Use the most accurate DCT/IDCT algorithm available.

The default if this flag is not specified is implementation-specific. For example, the implementation of the TurboJPEG API in libjpeg-turbo uses the fast algorithm by default when compressing, because this has been shown to have only a very slight effect on accuracy, but it uses the accurate algorithm when decompressing, because this has been shown to have a larger effect.

## ◆ TJFLAG_BOTTOMUP

#define TJFLAG_BOTTOMUP

Rows in the packed-pixel source/destination image are stored in bottom-up (Windows, OpenGL) order rather than in top-down (X11) order.

## ◆ TJFLAG_FASTDCT

#define TJFLAG_FASTDCT

Use the fastest DCT/IDCT algorithm available.

The default if this flag is not specified is implementation-specific. For example, the implementation of the TurboJPEG API in libjpeg-turbo uses the fast algorithm by default when compressing, because this has been shown to have only a very slight effect on accuracy, but it uses the accurate algorithm when decompressing, because this has been shown to have a larger effect.

## ◆ TJFLAG_FASTUPSAMPLE

#define TJFLAG_FASTUPSAMPLE

When decompressing an image that was compressed using chrominance subsampling, use the fastest chrominance upsampling algorithm available.

The default is to use smooth upsampling, which creates a smooth transition between neighboring chrominance components in order to reduce upsampling artifacts in the decompressed image.

## ◆ TJFLAG_LIMITSCANS

#define TJFLAG_LIMITSCANS

Limit the number of progressive JPEG scans that the decompression and transform functions will process.

If a progressive JPEG image contains an unreasonably large number of scans, then this flag will cause the decompression and transform functions to return an error. The primary purpose of this is to allow security-critical applications to guard against an exploit of the progressive JPEG format described in this report.

## ◆ TJFLAG_NOREALLOC

#define TJFLAG_NOREALLOC

Disable JPEG buffer (re)allocation.

If passed to one of the JPEG compression or transform functions, this flag will cause those functions to generate an error if the JPEG destination buffer is invalid or too small, rather than attempt to allocate or reallocate that buffer.

## ◆ TJFLAG_PROGRESSIVE

#define TJFLAG_PROGRESSIVE

Use progressive entropy coding in JPEG images generated by the compression and transform functions.

Progressive entropy coding will generally improve compression relative to baseline entropy coding (the default), but it will reduce compression and decompression performance considerably.

## ◆ TJFLAG_STOPONWARNING

#define TJFLAG_STOPONWARNING

Immediately discontinue the current compression/decompression/transform operation if a warning (non-fatal error) occurs.

The default behavior is to allow the operation to complete unless a fatal error is encountered.

## ◆ TJPAD

#define TJPAD | ( |  | width | ) |

Pad the given width to the nearest multiple of 4.

## ◆ TJSCALED

#define TJSCALED | ( |  | dimension,
|  |  | scalingFactor
| ) |  |

Compute the scaled value of `dimension` using the given scaling factor.

This macro performs the integer equivalent of `ceil(dimension * scalingFactor)`.

## ◆ TJXOPT_COPYNONE

#define TJXOPT_COPYNONE

This option will prevent tjTransform() from copying any extra markers (including EXIF and ICC profile data) from the source image to the destination image.

## ◆ TJXOPT_CROP

#define TJXOPT_CROP

This option will enable lossless cropping.

See tjTransform() for more information.

## ◆ TJXOPT_GRAY

#define TJXOPT_GRAY

This option will discard the color data in the source image and produce a grayscale destination image.

## ◆ TJXOPT_NOOUTPUT

#define TJXOPT_NOOUTPUT

This option will prevent tjTransform() from outputting a JPEG image for this particular transform.

(This can be used in conjunction with a custom filter to capture the transformed DCT coefficients without transcoding them.)

## ◆ TJXOPT_PERFECT

#define TJXOPT_PERFECT

This option will cause tjTransform() to return an error if the transform is not perfect.

Lossless transforms operate on MCU blocks, whose size depends on the level of chrominance subsampling used (see tjMCUWidth and tjMCUHeight.) If the image's width or height is not evenly divisible by the MCU block size, then there will be partial MCU blocks on the right and/or bottom edges. It is not possible to move these partial MCU blocks to the top or left of the image, so any transform that would require that is "imperfect." If this option is not specified, then any partial MCU blocks that cannot be transformed will be left in place, which will create odd-looking strips on the right or bottom edge of the image.

## ◆ TJXOPT_PROGRESSIVE

#define TJXOPT_PROGRESSIVE

This option will enable progressive entropy coding in the JPEG image generated by this particular transform.

Progressive entropy coding will generally improve compression relative to baseline entropy coding (the default), but it will reduce decompression performance considerably.

## ◆ TJXOPT_TRIM

#define TJXOPT_TRIM

This option will cause tjTransform() to discard any partial MCU blocks that cannot be transformed.

## Typedef Documentation

## ◆ tjhandle

typedef void* tjhandle

TurboJPEG instance handle.

## ◆ tjtransform

typedef struct tjtransform tjtransform

Lossless transform.

## Enumeration Type Documentation

## ◆ TJCS

enum TJCS

JPEG colorspaces.

Enumerator
TJCS_RGB | RGB colorspace. When compressing the JPEG image, the R, G, and B components in the source image are reordered into image planes, but no colorspace conversion or subsampling is performed. RGB JPEG images can be decompressed to packed-pixel images with any of the extended RGB or grayscale pixel formats, but they cannot be decompressed to planar YUV images.
TJCS_YCbCr | YCbCr colorspace. YCbCr is not an absolute colorspace but rather a mathematical transformation of RGB designed solely for storage and transmission. YCbCr images must be converted to RGB before they can actually be displayed. In the YCbCr colorspace, the Y (luminance) component represents the black & white portion of the original image, and the Cb and Cr (chrominance) components represent the color portion of the original image. Originally, the analog equivalent of this transformation allowed the same signal to drive both black & white and color televisions, but JPEG images use YCbCr primarily because it allows the color data to be optionally subsampled for the purposes of reducing network or disk usage. YCbCr is the most common JPEG colorspace, and YCbCr JPEG images can be compressed from and decompressed to packed-pixel images with any of the extended RGB or grayscale pixel formats. YCbCr JPEG images can also be compressed from and decompressed to planar YUV images.
TJCS_GRAY | Grayscale colorspace. The JPEG image retains only the luminance data (Y component), and any color data from the source image is discarded. Grayscale JPEG images can be compressed from and decompressed to packed-pixel images with any of the extended RGB or grayscale pixel formats, or they can be compressed from and decompressed to planar YUV images.
TJCS_CMYK | CMYK colorspace. When compressing the JPEG image, the C, M, Y, and K components in the source image are reordered into image planes, but no colorspace conversion or subsampling is performed. CMYK JPEG images can only be decompressed to packed-pixel images with the CMYK pixel format.
TJCS_YCCK | YCCK colorspace. YCCK (AKA "YCbCrK") is not an absolute colorspace but rather a mathematical transformation of CMYK designed solely for storage and transmission. It is to CMYK as YCbCr is to RGB. CMYK pixels can be reversibly transformed into YCCK, and as with YCbCr, the chrominance components in the YCCK pixels can be subsampled without incurring major perceptual loss. YCCK JPEG images can only be compressed from and decompressed to packed-pixel images with the CMYK pixel format.

## ◆ TJERR

enum TJERR

Error codes.

Enumerator
TJERR_WARNING | The error was non-fatal and recoverable, but the destination image may still be corrupt.
TJERR_FATAL | The error was fatal and non-recoverable.

## ◆ TJPF

enum TJPF

Pixel formats.

Enumerator
TJPF_RGB | RGB pixel format. The red, green, and blue components in the image are stored in 3-byte pixels in the order R, G, B from lowest to highest byte address within each pixel.
TJPF_BGR | BGR pixel format. The red, green, and blue components in the image are stored in 3-byte pixels in the order B, G, R from lowest to highest byte address within each pixel.
TJPF_RGBX | RGBX pixel format. The red, green, and blue components in the image are stored in 4-byte pixels in the order R, G, B from lowest to highest byte address within each pixel. The X component is ignored when compressing and undefined when decompressing.
TJPF_BGRX | BGRX pixel format. The red, green, and blue components in the image are stored in 4-byte pixels in the order B, G, R from lowest to highest byte address within each pixel. The X component is ignored when compressing and undefined when decompressing.
TJPF_XBGR | XBGR pixel format. The red, green, and blue components in the image are stored in 4-byte pixels in the order R, G, B from highest to lowest byte address within each pixel. The X component is ignored when compressing and undefined when decompressing.
TJPF_XRGB | XRGB pixel format. The red, green, and blue components in the image are stored in 4-byte pixels in the order B, G, R from highest to lowest byte address within each pixel. The X component is ignored when compressing and undefined when decompressing.
TJPF_GRAY | Grayscale pixel format. Each 1-byte pixel represents a luminance (brightness) level from 0 to 255.
TJPF_RGBA | RGBA pixel format. This is the same as TJPF_RGBX, except that when decompressing, the X component is guaranteed to be 0xFF, which can be interpreted as an opaque alpha channel.
TJPF_BGRA | BGRA pixel format. This is the same as TJPF_BGRX, except that when decompressing, the X component is guaranteed to be 0xFF, which can be interpreted as an opaque alpha channel.
TJPF_ABGR | ABGR pixel format. This is the same as TJPF_XBGR, except that when decompressing, the X component is guaranteed to be 0xFF, which can be interpreted as an opaque alpha channel.
TJPF_ARGB | ARGB pixel format. This is the same as TJPF_XRGB, except that when decompressing, the X component is guaranteed to be 0xFF, which can be interpreted as an opaque alpha channel.
TJPF_CMYK | CMYK pixel format. Unlike RGB, which is an additive color model used primarily for display, CMYK (Cyan/Magenta/Yellow/Key) is a subtractive color model used primarily for printing. In the CMYK color model, the value of each color component typically corresponds to an amount of cyan, magenta, yellow, or black ink that is applied to a white background. In order to convert between CMYK and RGB, it is necessary to use a color management system (CMS.) A CMS will attempt to map colors within the printer's gamut to perceptually similar colors in the display's gamut and vice versa, but the mapping is typically not 1:1 or reversible, nor can it be defined with a simple formula. Thus, such a conversion is out of scope for a codec library. However, the TurboJPEG API allows for compressing packed-pixel CMYK images into YCCK JPEG images (see TJCS_YCCK) and decompressing YCCK JPEG images into packed-pixel CMYK images.
TJPF_UNKNOWN | Unknown pixel format. Currently this is only used by tjLoadImage().

## ◆ TJSAMP

enum TJSAMP

Chrominance subsampling options.

When pixels are converted from RGB to YCbCr (see TJCS_YCbCr) or from CMYK to YCCK (see TJCS_YCCK) as part of the JPEG compression process, some of the Cb and Cr (chrominance) components can be discarded or averaged together to produce a smaller image with little perceptible loss of image clarity. (The human eye is more sensitive to small changes in brightness than to small changes in color.) This is called "chrominance subsampling".

Enumerator
TJSAMP_444 | 4:4:4 chrominance subsampling (no chrominance subsampling). The JPEG or YUV image will contain one chrominance component for every pixel in the source image.
TJSAMP_422 | 4:2:2 chrominance subsampling. The JPEG or YUV image will contain one chrominance component for every 2x1 block of pixels in the source image.
TJSAMP_420 | 4:2:0 chrominance subsampling. The JPEG or YUV image will contain one chrominance component for every 2x2 block of pixels in the source image.
TJSAMP_GRAY | Grayscale. The JPEG or YUV image will contain no chrominance components.
TJSAMP_440 | 4:4:0 chrominance subsampling. The JPEG or YUV image will contain one chrominance component for every 1x2 block of pixels in the source image. Note 4:4:0 subsampling is not fully accelerated in libjpeg-turbo.
TJSAMP_411 | 4:1:1 chrominance subsampling. The JPEG or YUV image will contain one chrominance component for every 4x1 block of pixels in the source image. JPEG images compressed with 4:1:1 subsampling will be almost exactly the same size as those compressed with 4:2:0 subsampling, and in the aggregate, both subsampling methods produce approximately the same perceptual quality. However, 4:1:1 is better able to reproduce sharp horizontal features. Note 4:1:1 subsampling is not fully accelerated in libjpeg-turbo.

## ◆ TJXOP

enum TJXOP

Transform operations for tjTransform()

Enumerator
TJXOP_NONE | Do not transform the position of the image pixels.
TJXOP_HFLIP | Flip (mirror) image horizontally. This transform is imperfect if there are any partial MCU blocks on the right edge (see TJXOPT_PERFECT.)
TJXOP_VFLIP | Flip (mirror) image vertically. This transform is imperfect if there are any partial MCU blocks on the bottom edge (see TJXOPT_PERFECT.)
TJXOP_TRANSPOSE | Transpose image (flip/mirror along upper left to lower right axis.) This transform is always perfect.
TJXOP_TRANSVERSE | Transverse transpose image (flip/mirror along upper right to lower left axis.) This transform is imperfect if there are any partial MCU blocks in the image (see TJXOPT_PERFECT.)
TJXOP_ROT90 | Rotate image clockwise by 90 degrees. This transform is imperfect if there are any partial MCU blocks on the bottom edge (see TJXOPT_PERFECT.)
TJXOP_ROT180 | Rotate image 180 degrees. This transform is imperfect if there are any partial MCU blocks in the image (see TJXOPT_PERFECT.)
TJXOP_ROT270 | Rotate image counter-clockwise by 90 degrees. This transform is imperfect if there are any partial MCU blocks on the right edge (see TJXOPT_PERFECT.)

## Function Documentation

## ◆ tjAlloc()

DLLEXPORT unsigned char* tjAlloc | ( | int | bytes | ) |

Allocate a byte buffer for use with TurboJPEG.

You should always use this function to allocate the JPEG destination buffer(s) for the compression and transform functions unless you are disabling automatic buffer (re)allocation (by setting TJFLAG_NOREALLOC.)

Parameters

  bytes | the number of bytes to allocate

Returns
  a pointer to a newly-allocated buffer with the specified number of bytes.

See also
  tjFree()

## ◆ tjBufSize()

DLLEXPORT unsigned long tjBufSize | ( | int | width,
|  | int | height,
|  | int | jpegSubsamp
| ) |  |

The maximum size of the buffer (in bytes) required to hold a JPEG image with the given parameters.

The number of bytes returned by this function is larger than the size of the uncompressed source image. The reason for this is that the JPEG format uses 16-bit coefficients, so it is possible for a very high-quality source image with very high-frequency content to expand rather than compress when converted to the JPEG format. Such images represent very rare corner cases, but since there is no way to predict the size of a JPEG image prior to compression, the corner cases have to be handled.

Parameters

  width | width (in pixels) of the image
  height | height (in pixels) of the image
  jpegSubsamp | the level of chrominance subsampling to be used when generating the JPEG image (see Chrominance subsampling options.)

Returns
  the maximum size of the buffer (in bytes) required to hold the image, or -1 if the arguments are out of bounds.

## ◆ tjBufSizeYUV2()

DLLEXPORT unsigned long tjBufSizeYUV2 | ( | int | width,
|  | int | align,
|  | int | height,
|  | int | subsamp
| ) |  |

The size of the buffer (in bytes) required to hold a unified planar YUV image with the given parameters.

Parameters

  width | width (in pixels) of the image
  align | row alignment (in bytes) of the image (must be a power of 2.) Setting this parameter to n specifies that each row in each plane of the image will be padded to the nearest multiple of n bytes (1 = unpadded.)
  height | height (in pixels) of the image
  subsamp | level of chrominance subsampling in the image (see Chrominance subsampling options.)

Returns
  the size of the buffer (in bytes) required to hold the image, or -1 if the arguments are out of bounds.

## ◆ tjCompress2()

DLLEXPORT int tjCompress2 | ( | tjhandle | handle,
|  | const unsigned char * | srcBuf,
|  | int | width,
|  | int | pitch,
|  | int | height,
|  | int | pixelFormat,
|  | unsigned char ** | jpegBuf,
|  | unsigned long * | jpegSize,
|  | int | jpegSubsamp,
|  | int | jpegQual,
|  | int | flags
| ) |  |

Compress a packed-pixel RGB, grayscale, or CMYK image into a JPEG image.

Parameters

  handle | a handle to a TurboJPEG compressor or transformer instance
  srcBuf | pointer to a buffer containing a packed-pixel RGB, grayscale, or CMYK source image to be compressed
  width | width (in pixels) of the source image
  pitch | bytes per row in the source image. Normally this should be `width * tjPixelSize[pixelFormat]`, if the image is unpadded, or `TJPAD(width * tjPixelSize[pixelFormat])` if each row of the image is padded to the nearest multiple of 4 bytes, as is the case for Windows bitmaps. You can also be clever and use this parameter to skip rows, etc. Setting this parameter to 0 is the equivalent of setting it to `width * tjPixelSize[pixelFormat]`.
  height | height (in pixels) of the source image
  pixelFormat | pixel format of the source image (see Pixel formats.)
  jpegBuf | address of a pointer to a byte buffer that will receive the JPEG image. TurboJPEG has the ability to reallocate the JPEG buffer to accommodate the size of the JPEG image. Thus, you can choose to: pre-allocate the JPEG buffer with an arbitrary size using tjAlloc() and let TurboJPEG grow the buffer as needed, set `*jpegBuf` to NULL to tell TurboJPEG to allocate the buffer for you, or pre-allocate the buffer to a "worst case" size determined by calling tjBufSize(). This should ensure that the buffer never has to be re-allocated. (Setting TJFLAG_NOREALLOC guarantees that it won't be.) If you choose option 1, then `*jpegSize` should be set to the size of your pre-allocated buffer. In any case, unless you have set TJFLAG_NOREALLOC, you should always check `*jpegBuf` upon return from this function, as it may have changed.
  jpegSize | pointer to an unsigned long variable that holds the size of the JPEG buffer. If `*jpegBuf` points to a pre-allocated buffer, then `*jpegSize` should be set to the size of the buffer. Upon return, `*jpegSize` will contain the size of the JPEG image (in bytes.) If `*jpegBuf` points to a JPEG buffer that is being reused from a previous call to one of the JPEG compression functions, then `*jpegSize` is ignored.
  jpegSubsamp | the level of chrominance subsampling to be used when generating the JPEG image (see Chrominance subsampling options.)
  jpegQual | the image quality of the generated JPEG image (1 = worst, 100 = best)
  flags | the bitwise OR of one or more of the flags

Returns
  0 if successful, or -1 if an error occurred (see tjGetErrorStr2() and tjGetErrorCode().)

## ◆ tjCompressFromYUV()

DLLEXPORT int tjCompressFromYUV | ( | tjhandle | handle,
|  | const unsigned char * | srcBuf,
|  | int | width,
|  | int | align,
|  | int | height,
|  | int | subsamp,
|  | unsigned char ** | jpegBuf,
|  | unsigned long * | jpegSize,
|  | int | jpegQual,
|  | int | flags
| ) |  |

Compress a unified planar YUV image into a JPEG image.

Parameters

  handle | a handle to a TurboJPEG compressor or transformer instance
  srcBuf | pointer to a buffer containing a unified planar YUV source image to be compressed. The size of this buffer should match the value returned by tjBufSizeYUV2() for the given image width, height, row alignment, and level of chrominance subsampling. The Y, U (Cb), and V (Cr) image planes should be stored sequentially in the buffer. (Refer to YUV Image Format Notes.)
  width | width (in pixels) of the source image. If the width is not an even multiple of the MCU block width (see tjMCUWidth), then an intermediate buffer copy will be performed.
  align | row alignment (in bytes) of the source image (must be a power of 2.) Setting this parameter to n indicates that each row in each plane of the source image is padded to the nearest multiple of n bytes (1 = unpadded.)
  height | height (in pixels) of the source image. If the height is not an even multiple of the MCU block height (see tjMCUHeight), then an intermediate buffer copy will be performed.
  subsamp | the level of chrominance subsampling used in the source image (see Chrominance subsampling options.)
  jpegBuf | address of a pointer to a byte buffer that will receive the JPEG image. TurboJPEG has the ability to reallocate the JPEG buffer to accommodate the size of the JPEG image. Thus, you can choose to: pre-allocate the JPEG buffer with an arbitrary size using tjAlloc() and let TurboJPEG grow the buffer as needed, set `*jpegBuf` to NULL to tell TurboJPEG to allocate the buffer for you, or pre-allocate the buffer to a "worst case" size determined by calling tjBufSize(). This should ensure that the buffer never has to be re-allocated. (Setting TJFLAG_NOREALLOC guarantees that it won't be.) If you choose option 1, then `*jpegSize` should be set to the size of your pre-allocated buffer. In any case, unless you have set TJFLAG_NOREALLOC, you should always check `*jpegBuf` upon return from this function, as it may have changed.
  jpegSize | pointer to an unsigned long variable that holds the size of the JPEG buffer. If `*jpegBuf` points to a pre-allocated buffer, then `*jpegSize` should be set to the size of the buffer. Upon return, `*jpegSize` will contain the size of the JPEG image (in bytes.) If `*jpegBuf` points to a JPEG buffer that is being reused from a previous call to one of the JPEG compression functions, then `*jpegSize` is ignored.
  jpegQual | the image quality of the generated JPEG image (1 = worst, 100 = best)
  flags | the bitwise OR of one or more of the flags

Returns
  0 if successful, or -1 if an error occurred (see tjGetErrorStr2() and tjGetErrorCode().)

## ◆ tjCompressFromYUVPlanes()

DLLEXPORT int tjCompressFromYUVPlanes | ( | tjhandle | handle,
|  | const unsigned char ** | srcPlanes,
|  | int | width,
|  | const int * | strides,
|  | int | height,
|  | int | subsamp,
|  | unsigned char ** | jpegBuf,
|  | unsigned long * | jpegSize,
|  | int | jpegQual,
|  | int | flags
| ) |  |

Compress a set of Y, U (Cb), and V (Cr) image planes into a JPEG image.

Parameters

  handle | a handle to a TurboJPEG compressor or transformer instance
  srcPlanes | an array of pointers to Y, U (Cb), and V (Cr) image planes (or just a Y plane, if compressing a grayscale image) that contain a YUV source image to be compressed. These planes can be contiguous or non-contiguous in memory. The size of each plane should match the value returned by tjPlaneSizeYUV() for the given image width, height, strides, and level of chrominance subsampling. Refer to YUV Image Format Notes for more details.
  width | width (in pixels) of the source image. If the width is not an even multiple of the MCU block width (see tjMCUWidth), then an intermediate buffer copy will be performed.
  strides | an array of integers, each specifying the number of bytes per row in the corresponding plane of the YUV source image. Setting the stride for any plane to 0 is the same as setting it to the plane width (see YUV Image Format Notes.) If `strides` is NULL, then the strides for all planes will be set to their respective plane widths. You can adjust the strides in order to specify an arbitrary amount of row padding in each plane or to create a JPEG image from a subregion of a larger planar YUV image.
  height | height (in pixels) of the source image. If the height is not an even multiple of the MCU block height (see tjMCUHeight), then an intermediate buffer copy will be performed.
  subsamp | the level of chrominance subsampling used in the source image (see Chrominance subsampling options.)
  jpegBuf | address of a pointer to a byte buffer that will receive the JPEG image. TurboJPEG has the ability to reallocate the JPEG buffer to accommodate the size of the JPEG image. Thus, you can choose to: pre-allocate the JPEG buffer with an arbitrary size using tjAlloc() and let TurboJPEG grow the buffer as needed, set `*jpegBuf` to NULL to tell TurboJPEG to allocate the buffer for you, or pre-allocate the buffer to a "worst case" size determined by calling tjBufSize(). This should ensure that the buffer never has to be re-allocated. (Setting TJFLAG_NOREALLOC guarantees that it won't be.) If you choose option 1, then `*jpegSize` should be set to the size of your pre-allocated buffer. In any case, unless you have set TJFLAG_NOREALLOC, you should always check `*jpegBuf` upon return from this function, as it may have changed.
  jpegSize | pointer to an unsigned long variable that holds the size of the JPEG buffer. If `*jpegBuf` points to a pre-allocated buffer, then `*jpegSize` should be set to the size of the buffer. Upon return, `*jpegSize` will contain the size of the JPEG image (in bytes.) If `*jpegBuf` points to a JPEG buffer that is being reused from a previous call to one of the JPEG compression functions, then `*jpegSize` is ignored.
  jpegQual | the image quality of the generated JPEG image (1 = worst, 100 = best)
  flags | the bitwise OR of one or more of the flags

Returns
  0 if successful, or -1 if an error occurred (see tjGetErrorStr2() and tjGetErrorCode().)

## ◆ tjDecodeYUV()

DLLEXPORT int tjDecodeYUV | ( | tjhandle | handle,
|  | const unsigned char * | srcBuf,
|  | int | align,
|  | int | subsamp,
|  | unsigned char * | dstBuf,
|  | int | width,
|  | int | pitch,
|  | int | height,
|  | int | pixelFormat,
|  | int | flags
| ) |  |

Decode a unified planar YUV image into a packed-pixel RGB or grayscale image.

This function performs color conversion (which is accelerated in the libjpeg-turbo implementation) but does not execute any of the other steps in the JPEG decompression process.

Parameters

  handle | a handle to a TurboJPEG decompressor or transformer instance
  srcBuf | pointer to a buffer containing a unified planar YUV source image to be decoded. The size of this buffer should match the value returned by tjBufSizeYUV2() for the given image width, height, row alignment, and level of chrominance subsampling. The Y, U (Cb), and V (Cr) image planes should be stored sequentially in the source buffer. (Refer to YUV Image Format Notes.)
  align | row alignment (in bytes) of the YUV source image (must be a power of 2.) Setting this parameter to n indicates that each row in each plane of the YUV source image is padded to the nearest multiple of n bytes (1 = unpadded.)
  subsamp | the level of chrominance subsampling used in the YUV source image (see Chrominance subsampling options.)
  dstBuf | pointer to a buffer that will receive the packed-pixel decoded image. This buffer should normally be `pitch * height` bytes in size, but the `dstBuf` pointer can also be used to decode into a specific region of a larger buffer.
  width | width (in pixels) of the source and destination images
  pitch | bytes per row in the destination image. Normally this should be set to `width * tjPixelSize[pixelFormat]`, if the destination image should be unpadded, or `TJPAD(width * tjPixelSize[pixelFormat])` if each row of the destination image should be padded to the nearest multiple of 4 bytes, as is the case for Windows bitmaps. You can also be clever and use the pitch parameter to skip rows, etc. Setting this parameter to 0 is the equivalent of setting it to `width * tjPixelSize[pixelFormat]`.
  height | height (in pixels) of the source and destination images
  pixelFormat | pixel format of the destination image (see Pixel formats.)
  flags | the bitwise OR of one or more of the flags

Returns
  0 if successful, or -1 if an error occurred (see tjGetErrorStr2() and tjGetErrorCode().)

## ◆ tjDecodeYUVPlanes()

DLLEXPORT int tjDecodeYUVPlanes | ( | tjhandle | handle,
|  | const unsigned char ** | srcPlanes,
|  | const int * | strides,
|  | int | subsamp,
|  | unsigned char * | dstBuf,
|  | int | width,
|  | int | pitch,
|  | int | height,
|  | int | pixelFormat,
|  | int | flags
| ) |  |

Decode a set of Y, U (Cb), and V (Cr) image planes into a packed-pixel RGB or grayscale image.

This function performs color conversion (which is accelerated in the libjpeg-turbo implementation) but does not execute any of the other steps in the JPEG decompression process.

Parameters

  handle | a handle to a TurboJPEG decompressor or transformer instance
  srcPlanes | an array of pointers to Y, U (Cb), and V (Cr) image planes (or just a Y plane, if decoding a grayscale image) that contain a YUV image to be decoded. These planes can be contiguous or non-contiguous in memory. The size of each plane should match the value returned by tjPlaneSizeYUV() for the given image width, height, strides, and level of chrominance subsampling. Refer to YUV Image Format Notes for more details.
  strides | an array of integers, each specifying the number of bytes per row in the corresponding plane of the YUV source image. Setting the stride for any plane to 0 is the same as setting it to the plane width (see YUV Image Format Notes.) If `strides` is NULL, then the strides for all planes will be set to their respective plane widths. You can adjust the strides in order to specify an arbitrary amount of row padding in each plane or to decode a subregion of a larger planar YUV image.
  subsamp | the level of chrominance subsampling used in the YUV source image (see Chrominance subsampling options.)
  dstBuf | pointer to a buffer that will receive the packed-pixel decoded image. This buffer should normally be `pitch * height` bytes in size, but the `dstBuf` pointer can also be used to decode into a specific region of a larger buffer.
  width | width (in pixels) of the source and destination images
  pitch | bytes per row in the destination image. Normally this should be set to `width * tjPixelSize[pixelFormat]`, if the destination image should be unpadded, or `TJPAD(width * tjPixelSize[pixelFormat])` if each row of the destination image should be padded to the nearest multiple of 4 bytes, as is the case for Windows bitmaps. You can also be clever and use the pitch parameter to skip rows, etc. Setting this parameter to 0 is the equivalent of setting it to `width * tjPixelSize[pixelFormat]`.
  height | height (in pixels) of the source and destination images
  pixelFormat | pixel format of the destination image (see Pixel formats.)
  flags | the bitwise OR of one or more of the flags

Returns
  0 if successful, or -1 if an error occurred (see tjGetErrorStr2() and tjGetErrorCode().)

## ◆ tjDecompress2()

DLLEXPORT int tjDecompress2 | ( | tjhandle | handle,
|  | const unsigned char * | jpegBuf,
|  | unsigned long | jpegSize,
|  | unsigned char * | dstBuf,
|  | int | width,
|  | int | pitch,
|  | int | height,
|  | int | pixelFormat,
|  | int | flags
| ) |  |

Decompress a JPEG image into a packed-pixel RGB, grayscale, or CMYK image.

Parameters

  handle | a handle to a TurboJPEG decompressor or transformer instance
  jpegBuf | pointer to a byte buffer containing the JPEG image to decompress
  jpegSize | size of the JPEG image (in bytes)
  dstBuf | pointer to a buffer that will receive the packed-pixel decompressed image. This buffer should normally be `pitch * scaledHeight` bytes in size, where `scaledHeight` can be determined by calling TJSCALED() with the JPEG image height and one of the scaling factors returned by tjGetScalingFactors(). The `dstBuf` pointer may also be used to decompress into a specific region of a larger buffer.
  width | desired width (in pixels) of the destination image. If this is different than the width of the JPEG image being decompressed, then TurboJPEG will use scaling in the JPEG decompressor to generate the largest possible image that will fit within the desired width. If `width` is set to 0, then only the height will be considered when determining the scaled image size.
  pitch | bytes per row in the destination image. Normally this should be set to `scaledWidth * tjPixelSize[pixelFormat]`, if the destination image should be unpadded, or `TJPAD(scaledWidth * tjPixelSize[pixelFormat])` if each row of the destination image should be padded to the nearest multiple of 4 bytes, as is the case for Windows bitmaps. (NOTE: `scaledWidth` can be determined by calling TJSCALED() with the JPEG image width and one of the scaling factors returned by tjGetScalingFactors().) You can also be clever and use the pitch parameter to skip rows, etc. Setting this parameter to 0 is the equivalent of setting it to `scaledWidth * tjPixelSize[pixelFormat]`.
  height | desired height (in pixels) of the destination image. If this is different than the height of the JPEG image being decompressed, then TurboJPEG will use scaling in the JPEG decompressor to generate the largest possible image that will fit within the desired height. If `height` is set to 0, then only the width will be considered when determining the scaled image size.
  pixelFormat | pixel format of the destination image (see Pixel formats.)
  flags | the bitwise OR of one or more of the flags

Returns
  0 if successful, or -1 if an error occurred (see tjGetErrorStr2() and tjGetErrorCode().)

## ◆ tjDecompressHeader3()

DLLEXPORT int tjDecompressHeader3 | ( | tjhandle | handle,
|  | const unsigned char * | jpegBuf,
|  | unsigned long | jpegSize,
|  | int * | width,
|  | int * | height,
|  | int * | jpegSubsamp,
|  | int * | jpegColorspace
| ) |  |

Retrieve information about a JPEG image without decompressing it, or prime the decompressor with quantization and Huffman tables.

Parameters

  handle | a handle to a TurboJPEG decompressor or transformer instance
  jpegBuf | pointer to a byte buffer containing a JPEG image or an "abbreviated table specification" (AKA "tables-only") datastream. Passing a tables-only datastream to this function primes the decompressor with quantization and Huffman tables that can be used when decompressing subsequent "abbreviated image" datastreams. This is useful, for instance, when decompressing video streams in which all frames share the same quantization and Huffman tables.
  jpegSize | size of the JPEG image or tables-only datastream (in bytes)
  width | pointer to an integer variable that will receive the width (in pixels) of the JPEG image. If `jpegBuf` points to a tables-only datastream, then `width` is ignored.
  height | pointer to an integer variable that will receive the height (in pixels) of the JPEG image. If `jpegBuf` points to a tables-only datastream, then `height` is ignored.
  jpegSubsamp | pointer to an integer variable that will receive the level of chrominance subsampling used when the JPEG image was compressed (see Chrominance subsampling options.) If `jpegBuf` points to a tables-only datastream, then `jpegSubsamp` is ignored.
  jpegColorspace | pointer to an integer variable that will receive one of the JPEG colorspace constants, indicating the colorspace of the JPEG image (see JPEG colorspaces.) If `jpegBuf` points to a tables-only datastream, then `jpegColorspace` is ignored.

Returns
  0 if successful, or -1 if an error occurred (see tjGetErrorStr2() and tjGetErrorCode().)

## ◆ tjDecompressToYUV2()

DLLEXPORT int tjDecompressToYUV2 | ( | tjhandle | handle,
|  | const unsigned char * | jpegBuf,
|  | unsigned long | jpegSize,
|  | unsigned char * | dstBuf,
|  | int | width,
|  | int | align,
|  | int | height,
|  | int | flags
| ) |  |

Decompress a JPEG image into a unified planar YUV image.

This function performs JPEG decompression but leaves out the color conversion step, so a planar YUV image is generated instead of a packed-pixel image.

Parameters

  handle | a handle to a TurboJPEG decompressor or transformer instance
  jpegBuf | pointer to a byte buffer containing the JPEG image to decompress
  jpegSize | size of the JPEG image (in bytes)
  dstBuf | pointer to a buffer that will receive the unified planar YUV decompressed image. Use tjBufSizeYUV2() to determine the appropriate size for this buffer based on the scaled image width, scaled image height, row alignment, and level of chrominance subsampling. The Y, U (Cb), and V (Cr) image planes will be stored sequentially in the buffer. (Refer to YUV Image Format Notes.)
  width | desired width (in pixels) of the YUV image. If this is different than the width of the JPEG image being decompressed, then TurboJPEG will use scaling in the JPEG decompressor to generate the largest possible image that will fit within the desired width. If `width` is set to 0, then only the height will be considered when determining the scaled image size. If the scaled width is not an even multiple of the MCU block width (see tjMCUWidth), then an intermediate buffer copy will be performed.
  align | row alignment (in bytes) of the YUV image (must be a power of 2.) Setting this parameter to n will cause each row in each plane of the YUV image to be padded to the nearest multiple of n bytes (1 = unpadded.) To generate images suitable for X Video, `align` should be set to 4.
  height | desired height (in pixels) of the YUV image. If this is different than the height of the JPEG image being decompressed, then TurboJPEG will use scaling in the JPEG decompressor to generate the largest possible image that will fit within the desired height. If `height` is set to 0, then only the width will be considered when determining the scaled image size. If the scaled height is not an even multiple of the MCU block height (see tjMCUHeight), then an intermediate buffer copy will be performed.
  flags | the bitwise OR of one or more of the flags

Returns
  0 if successful, or -1 if an error occurred (see tjGetErrorStr2() and tjGetErrorCode().)

## ◆ tjDecompressToYUVPlanes()

DLLEXPORT int tjDecompressToYUVPlanes | ( | tjhandle | handle,
|  | const unsigned char * | jpegBuf,
|  | unsigned long | jpegSize,
|  | unsigned char ** | dstPlanes,
|  | int | width,
|  | int * | strides,
|  | int | height,
|  | int | flags
| ) |  |

Decompress a JPEG image into separate Y, U (Cb), and V (Cr) image planes.

This function performs JPEG decompression but leaves out the color conversion step, so a planar YUV image is generated instead of a packed-pixel image.

Parameters

  handle | a handle to a TurboJPEG decompressor or transformer instance
  jpegBuf | pointer to a byte buffer containing the JPEG image to decompress
  jpegSize | size of the JPEG image (in bytes)
  dstPlanes | an array of pointers to Y, U (Cb), and V (Cr) image planes (or just a Y plane, if decompressing a grayscale image) that will receive the decompressed image. These planes can be contiguous or non-contiguous in memory. Use tjPlaneSizeYUV() to determine the appropriate size for each plane based on the scaled image width, scaled image height, strides, and level of chrominance subsampling. Refer to YUV Image Format Notes for more details.
  width | desired width (in pixels) of the YUV image. If this is different than the width of the JPEG image being decompressed, then TurboJPEG will use scaling in the JPEG decompressor to generate the largest possible image that will fit within the desired width. If `width` is set to 0, then only the height will be considered when determining the scaled image size. If the scaled width is not an even multiple of the MCU block width (see tjMCUWidth), then an intermediate buffer copy will be performed.
  strides | an array of integers, each specifying the number of bytes per row in the corresponding plane of the YUV image. Setting the stride for any plane to 0 is the same as setting it to the scaled plane width (see YUV Image Format Notes.) If `strides` is NULL, then the strides for all planes will be set to their respective scaled plane widths. You can adjust the strides in order to add an arbitrary amount of row padding to each plane or to decompress the JPEG image into a subregion of a larger planar YUV image.
  height | desired height (in pixels) of the YUV image. If this is different than the height of the JPEG image being decompressed, then TurboJPEG will use scaling in the JPEG decompressor to generate the largest possible image that will fit within the desired height. If `height` is set to 0, then only the width will be considered when determining the scaled image size. If the scaled height is not an even multiple of the MCU block height (see tjMCUHeight), then an intermediate buffer copy will be performed.
  flags | the bitwise OR of one or more of the flags

Returns
  0 if successful, or -1 if an error occurred (see tjGetErrorStr2() and tjGetErrorCode().)

## ◆ tjDestroy()

DLLEXPORT int tjDestroy | ( | tjhandle | handle | ) |

Destroy a TurboJPEG compressor, decompressor, or transformer instance.

Parameters

  handle | a handle to a TurboJPEG compressor, decompressor or transformer instance

Returns
  0 if successful, or -1 if an error occurred (see tjGetErrorStr2().)

## ◆ tjEncodeYUV3()

DLLEXPORT int tjEncodeYUV3 | ( | tjhandle | handle,
|  | const unsigned char * | srcBuf,
|  | int | width,
|  | int | pitch,
|  | int | height,
|  | int | pixelFormat,
|  | unsigned char * | dstBuf,
|  | int | align,
|  | int | subsamp,
|  | int | flags
| ) |  |

Encode a packed-pixel RGB or grayscale image into a unified planar YUV image.

This function performs color conversion (which is accelerated in the libjpeg-turbo implementation) but does not execute any of the other steps in the JPEG compression process.

Parameters

  handle | a handle to a TurboJPEG compressor or transformer instance
  srcBuf | pointer to a buffer containing a packed-pixel RGB or grayscale source image to be encoded
  width | width (in pixels) of the source image
  pitch | bytes per row in the source image. Normally this should be `width * tjPixelSize[pixelFormat]`, if the image is unpadded, or `TJPAD(width * tjPixelSize[pixelFormat])` if each row of the image is padded to the nearest multiple of 4 bytes, as is the case for Windows bitmaps. You can also be clever and use this parameter to skip rows, etc. Setting this parameter to 0 is the equivalent of setting it to `width * tjPixelSize[pixelFormat]`.
  height | height (in pixels) of the source image
  pixelFormat | pixel format of the source image (see Pixel formats.)
  dstBuf | pointer to a buffer that will receive the unified planar YUV image. Use tjBufSizeYUV2() to determine the appropriate size for this buffer based on the image width, height, row alignment, and level of chrominance subsampling. The Y, U (Cb), and V (Cr) image planes will be stored sequentially in the buffer. (Refer to YUV Image Format Notes.)
  align | row alignment (in bytes) of the YUV image (must be a power of 2.) Setting this parameter to n will cause each row in each plane of the YUV image to be padded to the nearest multiple of n bytes (1 = unpadded.) To generate images suitable for X Video, `align` should be set to 4.
  subsamp | the level of chrominance subsampling to be used when generating the YUV image (see Chrominance subsampling options.) To generate images suitable for X Video, `subsamp` should be set to TJSAMP_420. This produces an image compatible with the I420 (AKA "YUV420P") format.
  flags | the bitwise OR of one or more of the flags

Returns
  0 if successful, or -1 if an error occurred (see tjGetErrorStr2() and tjGetErrorCode().)

## ◆ tjEncodeYUVPlanes()

DLLEXPORT int tjEncodeYUVPlanes | ( | tjhandle | handle,
|  | const unsigned char * | srcBuf,
|  | int | width,
|  | int | pitch,
|  | int | height,
|  | int | pixelFormat,
|  | unsigned char ** | dstPlanes,
|  | int * | strides,
|  | int | subsamp,
|  | int | flags
| ) |  |

Encode a packed-pixel RGB or grayscale image into separate Y, U (Cb), and V (Cr) image planes.

This function performs color conversion (which is accelerated in the libjpeg-turbo implementation) but does not execute any of the other steps in the JPEG compression process.

Parameters

  handle | a handle to a TurboJPEG compressor or transformer instance
  srcBuf | pointer to a buffer containing a packed-pixel RGB or grayscale source image to be encoded
  width | width (in pixels) of the source image
  pitch | bytes per row in the source image. Normally this should be `width * tjPixelSize[pixelFormat]`, if the image is unpadded, or `TJPAD(width * tjPixelSize[pixelFormat])` if each row of the image is padded to the nearest multiple of 4 bytes, as is the case for Windows bitmaps. You can also be clever and use this parameter to skip rows, etc. Setting this parameter to 0 is the equivalent of setting it to `width * tjPixelSize[pixelFormat]`.
  height | height (in pixels) of the source image
  pixelFormat | pixel format of the source image (see Pixel formats.)
  dstPlanes | an array of pointers to Y, U (Cb), and V (Cr) image planes (or just a Y plane, if generating a grayscale image) that will receive the encoded image. These planes can be contiguous or non-contiguous in memory. Use tjPlaneSizeYUV() to determine the appropriate size for each plane based on the image width, height, strides, and level of chrominance subsampling. Refer to YUV Image Format Notes for more details.
  strides | an array of integers, each specifying the number of bytes per row in the corresponding plane of the YUV image. Setting the stride for any plane to 0 is the same as setting it to the plane width (see YUV Image Format Notes.) If `strides` is NULL, then the strides for all planes will be set to their respective plane widths. You can adjust the strides in order to add an arbitrary amount of row padding to each plane or to encode an RGB or grayscale image into a subregion of a larger planar YUV image.
  subsamp | the level of chrominance subsampling to be used when generating the YUV image (see Chrominance subsampling options.) To generate images suitable for X Video, `subsamp` should be set to TJSAMP_420. This produces an image compatible with the I420 (AKA "YUV420P") format.
  flags | the bitwise OR of one or more of the flags

Returns
  0 if successful, or -1 if an error occurred (see tjGetErrorStr2() and tjGetErrorCode().)

## ◆ tjFree()

DLLEXPORT void tjFree | ( | unsigned char * | buffer | ) |

Free a byte buffer previously allocated by TurboJPEG.

You should always use this function to free JPEG destination buffer(s) that were automatically (re)allocated by the compression and transform functions or that were manually allocated using tjAlloc().

Parameters

  buffer | address of the buffer to free. If the address is NULL, then this function has no effect.

See also
  tjAlloc()

## ◆ tjGetErrorCode()

DLLEXPORT int tjGetErrorCode | ( | tjhandle | handle | ) |

Returns a code indicating the severity of the last error.

See Error codes.

Parameters

  handle | a handle to a TurboJPEG compressor, decompressor or transformer instance

Returns
  a code indicating the severity of the last error. See Error codes.

## ◆ tjGetErrorStr2()

DLLEXPORT char* tjGetErrorStr2 | ( | tjhandle | handle | ) |

Returns a descriptive error message explaining why the last command failed.

Parameters

  handle | a handle to a TurboJPEG compressor, decompressor, or transformer instance, or NULL if the error was generated by a global function (but note that retrieving the error message for a global function is thread-safe only on platforms that support thread-local storage.)

Returns
  a descriptive error message explaining why the last command failed.

## ◆ tjGetScalingFactors()

DLLEXPORT tjscalingfactor* tjGetScalingFactors | ( | int * | numScalingFactors | ) |

Returns a list of fractional scaling factors that the JPEG decompressor supports.

Parameters

  numScalingFactors | pointer to an integer variable that will receive the number of elements in the list

Returns
  a pointer to a list of fractional scaling factors, or NULL if an error is encountered (see tjGetErrorStr2().)

## ◆ tjInitCompress()

DLLEXPORT tjhandle tjInitCompress | ( | void |  | ) |

Create a TurboJPEG compressor instance.

Returns
  a handle to the newly-created instance, or NULL if an error occurred (see tjGetErrorStr2().)

## ◆ tjInitDecompress()

DLLEXPORT tjhandle tjInitDecompress | ( | void |  | ) |

Create a TurboJPEG decompressor instance.

Returns
  a handle to the newly-created instance, or NULL if an error occurred (see tjGetErrorStr2().)

## ◆ tjInitTransform()

DLLEXPORT tjhandle tjInitTransform | ( | void |  | ) |

Create a new TurboJPEG transformer instance.

Returns
  a handle to the newly-created instance, or NULL if an error occurred (see tjGetErrorStr2().)

## ◆ tjLoadImage()

DLLEXPORT unsigned char* tjLoadImage | ( | const char * | filename,
|  | int * | width,
|  | int | align,
|  | int * | height,
|  | int * | pixelFormat,
|  | int | flags
| ) |  |

Load a packed-pixel image from disk into memory.

Parameters

  filename | name of a file containing a packed-pixel image in Windows BMP or PBMPLUS (PPM/PGM) format
  width | pointer to an integer variable that will receive the width (in pixels) of the packed-pixel image
  align | row alignment of the packed-pixel buffer to be returned (must be a power of 2.) Setting this parameter to n will cause all rows in the buffer to be padded to the nearest multiple of n bytes (1 = unpadded.)
  height | pointer to an integer variable that will receive the height (in pixels) of the packed-pixel image
  pixelFormat | pointer to an integer variable that specifies or will receive the pixel format of the packed-pixel buffer. The behavior of tjLoadImage() will vary depending on the value of `*pixelFormat` passed to the function: TJPF_UNKNOWN : The packed-pixel buffer returned by this function will use the most optimal pixel format for the file type, and `*pixelFormat` will contain the ID of that pixel format upon successful return from this function. TJPF_GRAY : Only PGM files and 8-bit-per-pixel BMP files with a grayscale colormap can be loaded. TJPF_CMYK : The RGB or grayscale pixels stored in the file will be converted using a quick & dirty algorithm that is suitable only for testing purposes. (Proper conversion between CMYK and other formats requires a color management system.) Other pixel formats : The packed-pixel buffer will use the specified pixel format, and pixel format conversion will be performed if necessary.
  flags | the bitwise OR of one or more of the flags.

Returns
  a pointer to a newly-allocated buffer containing the packed-pixel image, converted to the chosen pixel format and with the chosen row alignment, or NULL if an error occurred (see tjGetErrorStr2().) This buffer should be freed using tjFree().

## ◆ tjPlaneHeight()

DLLEXPORT int tjPlaneHeight | ( | int | componentID,
|  | int | height,
|  | int | subsamp
| ) |  |

The plane height of a YUV image plane with the given parameters.

Refer to YUV Image Format Notes for a description of plane height.

Parameters

  componentID | ID number of the image plane (0 = Y, 1 = U/Cb, 2 = V/Cr)
  height | height (in pixels) of the YUV image
  subsamp | level of chrominance subsampling in the image (see Chrominance subsampling options.)

Returns
  the plane height of a YUV image plane with the given parameters, or -1 if the arguments are out of bounds.

## ◆ tjPlaneSizeYUV()

DLLEXPORT unsigned long tjPlaneSizeYUV | ( | int | componentID,
|  | int | width,
|  | int | stride,
|  | int | height,
|  | int | subsamp
| ) |  |

The size of the buffer (in bytes) required to hold a YUV image plane with the given parameters.

Parameters

  componentID | ID number of the image plane (0 = Y, 1 = U/Cb, 2 = V/Cr)
  width | width (in pixels) of the YUV image. NOTE: this is the width of the whole image, not the plane width.
  stride | bytes per row in the image plane. Setting this to 0 is the equivalent of setting it to the plane width.
  height | height (in pixels) of the YUV image. NOTE: this is the height of the whole image, not the plane height.
  subsamp | level of chrominance subsampling in the image (see Chrominance subsampling options.)

Returns
  the size of the buffer (in bytes) required to hold the YUV image plane, or -1 if the arguments are out of bounds.

## ◆ tjPlaneWidth()

DLLEXPORT int tjPlaneWidth | ( | int | componentID,
|  | int | width,
|  | int | subsamp
| ) |  |

The plane width of a YUV image plane with the given parameters.

Refer to YUV Image Format Notes for a description of plane width.

Parameters

  componentID | ID number of the image plane (0 = Y, 1 = U/Cb, 2 = V/Cr)
  width | width (in pixels) of the YUV image
  subsamp | level of chrominance subsampling in the image (see Chrominance subsampling options.)

Returns
  the plane width of a YUV image plane with the given parameters, or -1 if the arguments are out of bounds.

## ◆ tjSaveImage()

DLLEXPORT int tjSaveImage | ( | const char * | filename,
|  | unsigned char * | buffer,
|  | int | width,
|  | int | pitch,
|  | int | height,
|  | int | pixelFormat,
|  | int | flags
| ) |  |

Save a packed-pixel image from memory to disk.

Parameters

  filename | name of a file to which to save the packed-pixel image. The image will be stored in Windows BMP or PBMPLUS (PPM/PGM) format, depending on the file extension.
  buffer | pointer to a buffer containing a packed-pixel RGB, grayscale, or CMYK image to be saved
  width | width (in pixels) of the packed-pixel image
  pitch | bytes per row in the packed-pixel image. Setting this parameter to 0 is the equivalent of setting it to `width * tjPixelSize[pixelFormat]`.
  height | height (in pixels) of the packed-pixel image
  pixelFormat | pixel format of the packed-pixel image (see Pixel formats.) If this parameter is set to TJPF_GRAY, then the image will be stored in PGM or 8-bit-per-pixel (indexed color) BMP format. Otherwise, the image will be stored in PPM or 24-bit-per-pixel BMP format. If this parameter is set to TJPF_CMYK, then the CMYK pixels will be converted to RGB using a quick & dirty algorithm that is suitable only for testing purposes. (Proper conversion between CMYK and other formats requires a color management system.)
  flags | the bitwise OR of one or more of the flags.

Returns
  0 if successful, or -1 if an error occurred (see tjGetErrorStr2().)

## ◆ tjTransform()

DLLEXPORT int tjTransform | ( | tjhandle | handle,
|  | const unsigned char * | jpegBuf,
|  | unsigned long | jpegSize,
|  | int | n,
|  | unsigned char ** | dstBufs,
|  | unsigned long * | dstSizes,
|  | tjtransform * | transforms,
|  | int | flags
| ) |  |

Losslessly transform a JPEG image into another JPEG image.

Lossless transforms work by moving the raw DCT coefficients from one JPEG image structure to another without altering the values of the coefficients. While this is typically faster than decompressing the image, transforming it, and re-compressing it, lossless transforms are not free. Each lossless transform requires reading and performing Huffman decoding on all of the coefficients in the source image, regardless of the size of the destination image. Thus, this function provides a means of generating multiple transformed images from the same source or applying multiple transformations simultaneously, in order to eliminate the need to read the source coefficients multiple times.

Parameters

  handle | a handle to a TurboJPEG transformer instance
  jpegBuf | pointer to a byte buffer containing the JPEG source image to transform
  jpegSize | size of the JPEG source image (in bytes)
  n | the number of transformed JPEG images to generate
  dstBufs | pointer to an array of n byte buffers. `dstBufs[i]` will receive a JPEG image that has been transformed using the parameters in `transforms[i]`. TurboJPEG has the ability to reallocate the JPEG destination buffer to accommodate the size of the transformed JPEG image. Thus, you can choose to: pre-allocate the JPEG destination buffer with an arbitrary size using tjAlloc() and let TurboJPEG grow the buffer as needed, set `dstBufs[i]` to NULL to tell TurboJPEG to allocate the buffer for you, or pre-allocate the buffer to a "worst case" size determined by calling tjBufSize() with the transformed or cropped width and height and the level of subsampling used in the source image. Under normal circumstances, this should ensure that the buffer never has to be re-allocated. (Setting TJFLAG_NOREALLOC guarantees that it won't be.) Note, however, that there are some rare cases (such as transforming images with a large amount of embedded EXIF or ICC profile data) in which the transformed JPEG image will be larger than the worst-case size, and TJFLAG_NOREALLOC cannot be used in those cases. If you choose option 1, then `dstSizes[i]` should be set to the size of your pre-allocated buffer. In any case, unless you have set TJFLAG_NOREALLOC, you should always check `dstBufs[i]` upon return from this function, as it may have changed.
  dstSizes | pointer to an array of n unsigned long variables that will receive the actual sizes (in bytes) of each transformed JPEG image. If `dstBufs[i]` points to a pre-allocated buffer, then `dstSizes[i]` should be set to the size of the buffer. Upon return, `dstSizes[i]` will contain the size of the transformed JPEG image (in bytes.)
  transforms | pointer to an array of n tjtransform structures, each of which specifies the transform parameters and/or cropping region for the corresponding transformed JPEG image.
  flags | the bitwise OR of one or more of the flags

Returns
  0 if successful, or -1 if an error occurred (see tjGetErrorStr2() and tjGetErrorCode().)

## Variable Documentation

## ◆ tjAlphaOffset

const int tjAlphaOffset[TJ_NUMPF]
| static

Alpha offset (in bytes) for a given pixel format.

This specifies the number of bytes that the alpha component is offset from the start of the pixel. For instance, if a pixel of format TJPF_BGRA is stored in `unsigned char pixel[]`, then the alpha component will be `pixel[tjAlphaOffset[TJPF_BGRA]]`. This will be -1 if the pixel format does not have an alpha component.

## ◆ tjBlueOffset

const int tjBlueOffset[TJ_NUMPF]
| static

Blue offset (in bytes) for a given pixel format.

This specifies the number of bytes that the blue component is offset from the start of the pixel. For instance, if a pixel of format TJPF_BGRX is stored in `unsigned char pixel[]`, then the blue component will be `pixel[tjBlueOffset[TJPF_BGRX]]`. This will be -1 if the pixel format does not have a blue component.

## ◆ tjGreenOffset

const int tjGreenOffset[TJ_NUMPF]
| static

Green offset (in bytes) for a given pixel format.

This specifies the number of bytes that the green component is offset from the start of the pixel. For instance, if a pixel of format TJPF_BGRX is stored in `unsigned char pixel[]`, then the green component will be `pixel[tjGreenOffset[TJPF_BGRX]]`. This will be -1 if the pixel format does not have a green component.

## ◆ tjMCUHeight

const int tjMCUHeight[TJ_NUMSAMP]
| static

MCU block height (in pixels) for a given level of chrominance subsampling.

MCU block sizes:

- 8x8 for no subsampling or grayscale
- 16x8 for 4:2:2
- 8x16 for 4:4:0
- 16x16 for 4:2:0
- 32x8 for 4:1:1

## ◆ tjMCUWidth

const int tjMCUWidth[TJ_NUMSAMP]
| static

MCU block width (in pixels) for a given level of chrominance subsampling.

MCU block sizes:

- 8x8 for no subsampling or grayscale
- 16x8 for 4:2:2
- 8x16 for 4:4:0
- 16x16 for 4:2:0
- 32x8 for 4:1:1

## ◆ tjPixelSize

const int tjPixelSize[TJ_NUMPF]
| static

Pixel size (in bytes) for a given pixel format.

## ◆ tjRedOffset

const int tjRedOffset[TJ_NUMPF]
| static

Red offset (in bytes) for a given pixel format.

This specifies the number of bytes that the red component is offset from the start of the pixel. For instance, if a pixel of format TJPF_BGRX is stored in `unsigned char pixel[]`, then the red component will be `pixel[tjRedOffset[TJPF_BGRX]]`. This will be -1 if the pixel format does not have a red component.