TurboJPEG

TurboJPEG API. More...

Data Structures
struct	tjscalingfactor
	Scaling factor. More...
struct	tjregion
	Cropping region. More...
struct	tjtransform
	Lossless transform. More...
Defines
#define	TJ_NUMSAMP
	The number of chrominance subsampling options.
#define	TJ_NUMPF
	The number of pixel formats.
#define	TJFLAG_BOTTOMUP
	The uncompressed source/destination image is stored in bottom-up (Windows, OpenGL) order, not top-down (X11) order.
#define	TJFLAG_FORCEMMX
	Turn off CPU auto-detection and force TurboJPEG to use MMX code (IPP and 32-bit libjpeg-turbo versions only.)
#define	TJFLAG_FORCESSE
	Turn off CPU auto-detection and force TurboJPEG to use SSE code (32-bit IPP and 32-bit libjpeg-turbo versions only)
#define	TJFLAG_FORCESSE2
	Turn off CPU auto-detection and force TurboJPEG to use SSE2 code (32-bit IPP and 32-bit libjpeg-turbo versions only)
#define	TJFLAG_FORCESSE3
	Turn off CPU auto-detection and force TurboJPEG to use SSE3 code (64-bit IPP version only)
#define	TJFLAG_FASTUPSAMPLE
	Use fast, inaccurate chrominance upsampling routines in the JPEG decompressor (libjpeg and libjpeg-turbo versions only)
#define	TJFLAG_NOREALLOC
	Disable buffer (re)allocation.
#define	TJ_NUMXOP
	Number of transform operations.
#define	TJXOPT_PERFECT
	This option will cause tjTransform() to return an error if the transform is not perfect.
#define	TJXOPT_TRIM
	This option will cause tjTransform() to discard any partial MCU blocks that cannot be transformed.
#define	TJXOPT_CROP
	This option will enable lossless cropping.
#define	TJXOPT_GRAY
	This option will discard the color data in the input image and produce a grayscale output image.
#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.)
#define	TJPAD(width)
	Pad the given width to the nearest 32-bit boundary.
#define	TJSCALED(dimension, scalingFactor)
	Compute the scaled value of dimension using the given scaling factor.
Typedefs
typedef struct tjtransform	tjtransform
	Lossless transform.
typedef void *	tjhandle
	TurboJPEG instance handle.
Enumerations
enum	TJSAMP {   TJSAMP_444, TJSAMP_422, TJSAMP_420, TJSAMP_GRAY,   TJSAMP_440 }
	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 }
	Pixel formats. 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 DLLCALL	tjInitCompress (void)
	Create a TurboJPEG compressor instance.
DLLEXPORT int DLLCALL	tjCompress2 (tjhandle handle, unsigned char *srcBuf, int width, int pitch, int height, int pixelFormat, unsigned char **jpegBuf, unsigned long *jpegSize, int jpegSubsamp, int jpegQual, int flags)
	Compress an RGB or grayscale image into a JPEG image.
DLLEXPORT unsigned long DLLCALL	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.
DLLEXPORT unsigned long DLLCALL	tjBufSizeYUV (int width, int height, int subsamp)
	The size of the buffer (in bytes) required to hold a YUV planar image with the given parameters.
DLLEXPORT int DLLCALL	tjEncodeYUV2 (tjhandle handle, unsigned char *srcBuf, int width, int pitch, int height, int pixelFormat, unsigned char *dstBuf, int subsamp, int flags)
	Encode an RGB or grayscale image into a YUV planar image.
DLLEXPORT tjhandle DLLCALL	tjInitDecompress (void)
	Create a TurboJPEG decompressor instance.
DLLEXPORT int DLLCALL	tjDecompressHeader2 (tjhandle handle, unsigned char *jpegBuf, unsigned long jpegSize, int *width, int *height, int *jpegSubsamp)
	Retrieve information about a JPEG image without decompressing it.
DLLEXPORT tjscalingfactor *DLLCALL	tjGetScalingFactors (int *numscalingfactors)
	Returns a list of fractional scaling factors that the JPEG decompressor in this implementation of TurboJPEG supports.
DLLEXPORT int DLLCALL	tjDecompress2 (tjhandle handle, unsigned char *jpegBuf, unsigned long jpegSize, unsigned char *dstBuf, int width, int pitch, int height, int pixelFormat, int flags)
	Decompress a JPEG image to an RGB or grayscale image.
DLLEXPORT int DLLCALL	tjDecompressToYUV (tjhandle handle, unsigned char *jpegBuf, unsigned long jpegSize, unsigned char *dstBuf, int flags)
	Decompress a JPEG image to a YUV planar image.
DLLEXPORT tjhandle DLLCALL	tjInitTransform (void)
	Create a new TurboJPEG transformer instance.
DLLEXPORT int DLLCALL	tjTransform (tjhandle handle, 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.
DLLEXPORT int DLLCALL	tjDestroy (tjhandle handle)
	Destroy a TurboJPEG compressor, decompressor, or transformer instance.
DLLEXPORT unsigned char *DLLCALL	tjAlloc (int bytes)
	Allocate an image buffer for use with TurboJPEG.
DLLEXPORT void DLLCALL	tjFree (unsigned char *buffer)
	Free an image buffer previously allocated by TurboJPEG.
DLLEXPORT char *DLLCALL	tjGetErrorStr (void)
	Returns a descriptive error message explaining why the last command failed.
Variables
static const int	tjMCUWidth [TJ_NUMSAMP]
	MCU block width (in pixels) for a given level of chrominance subsampling.
static const int	tjMCUHeight [TJ_NUMSAMP]
	MCU block height (in pixels) for a given level of chrominance subsampling.
static const int	tjRedOffset [TJ_NUMPF]
	Red offset (in bytes) for a given pixel format.
static const int	tjGreenOffset [TJ_NUMPF]
	Green offset (in bytes) for a given pixel format.
static const int	tjBlueOffset [TJ_NUMPF]
	Blue offset (in bytes) for a given pixel format.
static const int	tjPixelSize [TJ_NUMPF]
	Pixel size (in bytes) for a given pixel format.

---

Detailed Description

TurboJPEG API.

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

---

Define Documentation

#define TJ_NUMPF

The number of pixel formats.

#define TJ_NUMSAMP

The number of chrominance subsampling options.

#define TJ_NUMXOP

Number of transform operations.

#define TJFLAG_BOTTOMUP

The uncompressed source/destination image is stored in bottom-up (Windows, OpenGL) order, not top-down (X11) order.

#define TJFLAG_FASTUPSAMPLE

Use fast, inaccurate chrominance upsampling routines in the JPEG decompressor (libjpeg and libjpeg-turbo versions only)

#define TJFLAG_FORCEMMX

Turn off CPU auto-detection and force TurboJPEG to use MMX code (IPP and 32-bit libjpeg-turbo versions only.)

#define TJFLAG_FORCESSE

Turn off CPU auto-detection and force TurboJPEG to use SSE code (32-bit IPP and 32-bit libjpeg-turbo versions only)

#define TJFLAG_FORCESSE2

Turn off CPU auto-detection and force TurboJPEG to use SSE2 code (32-bit IPP and 32-bit libjpeg-turbo versions only)

#define TJFLAG_FORCESSE3

Turn off CPU auto-detection and force TurboJPEG to use SSE3 code (64-bit IPP version only)

#define TJFLAG_NOREALLOC

Disable buffer (re)allocation.

If passed to tjCompress2() or tjTransform(), this flag will cause those functions to generate an error if the JPEG image buffer is invalid or too small rather than attempting to allocate or reallocate that buffer. This reproduces the behavior of earlier versions of TurboJPEG.

#define TJPAD

(

width

)

Pad the given width to the nearest 32-bit boundary.

#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).

#define TJXOPT_CROP

This option will enable lossless cropping.

See tjTransform() for more information.

#define TJXOPT_GRAY

This option will discard the color data in the input image and produce a grayscale output image.

#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.)

#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.

#define TJXOPT_TRIM

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

---

Typedef Documentation

typedef void* tjhandle

TurboJPEG instance handle.

typedef struct tjtransform tjtransform

Lossless transform.

---

Enumeration Type Documentation

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.

enum TJSAMP

Chrominance subsampling options.

When an image is converted from the RGB to the YCbCr colorspace 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 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.

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

DLLEXPORT unsigned char* DLLCALL tjAlloc

(

int

bytes

)

Allocate an image buffer for use with TurboJPEG.

You should always use this function to allocate the JPEG destination buffer(s) for tjCompress2() and tjTransform() 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()

DLLEXPORT unsigned long DLLCALL 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, and it is thus possible for a very high-quality JPEG image with very high frequency content to expand rather than compress when converted to the JPEG format. Such images represent a very rare corner case, but since there is no way to predict the size of a JPEG image prior to compression, the corner case has to be handled.

Parameters:

width	width of the image (in pixels)
height	height of the image (in pixels)
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.

DLLEXPORT unsigned long DLLCALL tjBufSizeYUV	(	int	width,
		int	height,
		int	subsamp
	)

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

Parameters:

width	width of the image (in pixels)
height	height of the image (in pixels)
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.

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

Compress an RGB or grayscale image into a JPEG image.

Parameters:

handle	a handle to a TurboJPEG compressor or transformer instance
srcBuf	pointer to an image buffer containing RGB or grayscale pixels to be compressed
width	width (in pixels) of the source image
pitch	bytes per line of the source image. Normally, this should be width * tjPixelSize[pixelFormat] if the image is unpadded, or TJPAD(width * tjPixelSize[pixelFormat]) if each line of the image is padded to the nearest 32-bit boundary, as is the case for Windows bitmaps. You can also be clever and use this parameter to skip lines, 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 an image 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 this.) If you choose option 1, *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 image 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.)
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 tjGetErrorStr().)

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

Decompress a JPEG image to an RGB or grayscale image.

Parameters:

handle	a handle to a TurboJPEG decompressor or transformer instance
jpegBuf	pointer to a buffer containing the JPEG image to decompress
jpegSize	size of the JPEG image (in bytes)
dstBuf	pointer to an image buffer that will receive the 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 smaller 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 line of the destination image. Normally, this is scaledWidth * tjPixelSize[pixelFormat] if the decompressed image is unpadded, else TJPAD(scaledWidth * tjPixelSize[pixelFormat]) if each line of the decompressed image is padded to the nearest 32-bit boundary, 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 lines, 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 smaller 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 tjGetErrorStr().)

DLLEXPORT int DLLCALL tjDecompressHeader2	(	tjhandle	handle,
		unsigned char *	jpegBuf,
		unsigned long	jpegSize,
		int *	width,
		int *	height,
		int *	jpegSubsamp
	)

Retrieve information about a JPEG image without decompressing it.

Parameters:

handle	a handle to a TurboJPEG decompressor or transformer instance
jpegBuf	pointer to a buffer containing a JPEG image
jpegSize	size of the JPEG image (in bytes)
width	pointer to an integer variable that will receive the width (in pixels) of the JPEG image
height	pointer to an integer variable that will receive the height (in pixels) of the JPEG image
jpegSubsamp	pointer to an integer variable that will receive the level of chrominance subsampling used when compressing the JPEG image (see Chrominance subsampling options.)

Returns:

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

DLLEXPORT int DLLCALL tjDecompressToYUV	(	tjhandle	handle,
		unsigned char *	jpegBuf,
		unsigned long	jpegSize,
		unsigned char *	dstBuf,
		int	flags
	)

Decompress a JPEG image to a YUV planar image.

This function performs JPEG decompression but leaves out the color conversion step, so a planar YUV image is generated instead of an RGB image. The padding of the planes in this image is the same as the images generated by tjEncodeYUV2(). Note that, if the width or height of the image is not an even multiple of the MCU block size (see tjMCUWidth and tjMCUHeight), then an intermediate buffer copy will be performed within TurboJPEG.

Parameters:

handle	a handle to a TurboJPEG decompressor or transformer instance
jpegBuf	pointer to a buffer containing the JPEG image to decompress
jpegSize	size of the JPEG image (in bytes)
dstBuf	pointer to an image buffer that will receive the YUV image. Use tjBufSizeYUV to determine the appropriate size for this buffer based on the image width, height, and level of subsampling.
flags	the bitwise OR of one or more of the flags.

Returns:

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

DLLEXPORT int DLLCALL 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 tjGetErrorStr().)

DLLEXPORT int DLLCALL tjEncodeYUV2	(	tjhandle	handle,
		unsigned char *	srcBuf,
		int	width,
		int	pitch,
		int	height,
		int	pixelFormat,
		unsigned char *	dstBuf,
		int	subsamp,
		int	flags
	)

Encode an RGB or grayscale image into a YUV planar image.

This function uses the accelerated color conversion routines in TurboJPEG's underlying codec to produce a planar YUV image that is suitable for X Video. Specifically, if the chrominance components are subsampled along the horizontal dimension, then the width of the luminance plane is padded to 2 in the output image (same goes for the height of the luminance plane, if the chrominance components are subsampled along the vertical dimension.) Also, each line of each plane in the output image is padded to 4 bytes. Although this will work with any subsampling option, it is really only useful in combination with TJ_420, which produces an image compatible with the I420 (AKA "YUV420P") format.

Parameters:

handle	a handle to a TurboJPEG compressor or transformer instance
srcBuf	pointer to an image buffer containing RGB or grayscale pixels to be encoded
width	width (in pixels) of the source image
pitch	bytes per line of the source image. Normally, this should be width * tjPixelSize[pixelFormat] if the image is unpadded, or TJPAD(width * tjPixelSize[pixelFormat]) if each line of the image is padded to the nearest 32-bit boundary, as is the case for Windows bitmaps. You can also be clever and use this parameter to skip lines, 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 an image buffer that will receive the YUV image. Use tjBufSizeYUV() to determine the appropriate size for this buffer based on the image width, height, and level of chrominance subsampling.
subsamp	the level of chrominance subsampling to be used when generating the YUV image (see Chrominance subsampling options.)
flags	the bitwise OR of one or more of the flags.

Returns:

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

DLLEXPORT void DLLCALL tjFree

(

unsigned char *

buffer

)

Free an image buffer previously allocated by TurboJPEG.

You should always use this function to free JPEG destination buffer(s) that were automatically (re)allocated by tjCompress2() or tjTransform() or that were manually allocated using tjAlloc().

Parameters:

buffer

address of the buffer to free

See also:

tjAlloc()

DLLEXPORT char* DLLCALL tjGetErrorStr

(

void

)

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

Returns:

a descriptive error message explaining why the last command failed.

DLLEXPORT tjscalingfactor* DLLCALL tjGetScalingFactors

(

int *

numscalingfactors

)

Returns a list of fractional scaling factors that the JPEG decompressor in this implementation of TurboJPEG 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 tjGetErrorStr().)

DLLEXPORT tjhandle DLLCALL tjInitCompress

(

void

)

Create a TurboJPEG compressor instance.

Returns:

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

DLLEXPORT tjhandle DLLCALL tjInitDecompress

(

void

)

Create a TurboJPEG decompressor instance.

Returns:

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

DLLEXPORT tjhandle DLLCALL tjInitTransform

(

void

)

Create a new TurboJPEG transformer instance.

Returns:

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

DLLEXPORT int DLLCALL tjTransform	(	tjhandle	handle,
		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 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 Huffman decoding 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 of 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 buffer containing the JPEG image to transform
jpegSize	size of the JPEG image (in bytes)
n	the number of transformed JPEG images to generate
dstBufs	pointer to an array of n image 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 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 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 cropped width and height. This should ensure that the buffer never has to be re-allocated (setting TJFLAG_NOREALLOC guarantees this.) If you choose option 1, 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 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 output image.
flags	the bitwise OR of one or more of the flags.

Returns:

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

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Variable Documentation

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 TJ_BGRX is stored in char pixel[], then the blue component will be pixel[tjBlueOffset[TJ_BGRX]].

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 TJ_BGRX is stored in char pixel[], then the green component will be pixel[tjGreenOffset[TJ_BGRX]].

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

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

const int tjPixelSize[TJ_NUMPF] [static]

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

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 TJ_BGRX is stored in char pixel[], then the red component will be pixel[tjRedOffset[TJ_BGRX]].