jccolor.c - third_party/libjpeg-turbo - Git at Google

 /*
  * jccolor.c
  *
  * Copyright (C) 1991-1994, Thomas G. Lane.
  * This file is part of the Independent JPEG Group's software.
  * For conditions of distribution and use, see the accompanying README file.
  *
  * This file contains input colorspace conversion routines.
  */

 #define JPEG_INTERNALS
 #include "jinclude.h"
 #include "jpeglib.h"


 /* Private subobject */

 typedef struct {
   struct jpeg_color_converter pub; /* public fields */

   /* Private state for RGB->YCC conversion */
   INT32 * rgb_ycc_tab;		/* => table for RGB to YCbCr conversion */
 } my_color_converter;

 typedef my_color_converter * my_cconvert_ptr;


 /**************** RGB -> YCbCr conversion: most common case **************/

 /*
  * YCbCr is defined per CCIR 601-1, except that Cb and Cr are
  * normalized to the range 0..MAXJSAMPLE rather than -0.5 .. 0.5.
  * The conversion equations to be implemented are therefore
  *	Y  =  0.29900 * R + 0.58700 * G + 0.11400 * B
  *	Cb = -0.16874 * R - 0.33126 * G + 0.50000 * B  + CENTERJSAMPLE
  *	Cr =  0.50000 * R - 0.41869 * G - 0.08131 * B  + CENTERJSAMPLE
  * (These numbers are derived from TIFF 6.0 section 21, dated 3-June-92.)
  * Note: older versions of the IJG code used a zero offset of MAXJSAMPLE/2,
  * rather than CENTERJSAMPLE, for Cb and Cr.  This gave equal positive and
  * negative swings for Cb/Cr, but meant that grayscale values (Cb=Cr=0)
  * were not represented exactly.  Now we sacrifice exact representation of
  * maximum red and maximum blue in order to get exact grayscales.
  *
  * To avoid floating-point arithmetic, we represent the fractional constants
  * as integers scaled up by 2^16 (about 4 digits precision); we have to divide
  * the products by 2^16, with appropriate rounding, to get the correct answer.
  *
  * For even more speed, we avoid doing any multiplications in the inner loop
  * by precalculating the constants times R,G,B for all possible values.
  * For 8-bit JSAMPLEs this is very reasonable (only 256 entries per table);
  * for 12-bit samples it is still acceptable.  It's not very reasonable for
  * 16-bit samples, but if you want lossless storage you shouldn't be changing
  * colorspace anyway.
  * The CENTERJSAMPLE offsets and the rounding fudge-factor of 0.5 are included
  * in the tables to save adding them separately in the inner loop.
  */

 #define SCALEBITS	16	/* speediest right-shift on some machines */
 #define CBCR_OFFSET	((INT32) CENTERJSAMPLE << SCALEBITS)
 #define ONE_HALF	((INT32) 1 << (SCALEBITS-1))
 #define FIX(x)		((INT32) ((x) * (1L<<SCALEBITS) + 0.5))

 /* We allocate one big table and divide it up into eight parts, instead of
  * doing eight alloc_small requests.  This lets us use a single table base
  * address, which can be held in a register in the inner loops on many
  * machines (more than can hold all eight addresses, anyway).
  */

 #define R_Y_OFF		0			/* offset to R => Y section */
 #define G_Y_OFF		(1*(MAXJSAMPLE+1))	/* offset to G => Y section */
 #define B_Y_OFF		(2*(MAXJSAMPLE+1))	/* etc. */
 #define R_CB_OFF	(3*(MAXJSAMPLE+1))
 #define G_CB_OFF	(4*(MAXJSAMPLE+1))
 #define B_CB_OFF	(5*(MAXJSAMPLE+1))
 #define R_CR_OFF	B_CB_OFF		/* B=>Cb, R=>Cr are the same */
 #define G_CR_OFF	(6*(MAXJSAMPLE+1))
 #define B_CR_OFF	(7*(MAXJSAMPLE+1))
 #define TABLE_SIZE	(8*(MAXJSAMPLE+1))


 /*
  * Initialize for RGB->YCC colorspace conversion.
  */

 METHODDEF void
 rgb_ycc_start (j_compress_ptr cinfo)
 {
   my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
   INT32 * rgb_ycc_tab;
   INT32 i;

   /* Allocate and fill in the conversion tables. */
   cconvert->rgb_ycc_tab = rgb_ycc_tab = (INT32 *)
     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
 				(TABLE_SIZE * SIZEOF(INT32)));

   for (i = 0; i <= MAXJSAMPLE; i++) {
     rgb_ycc_tab[i+R_Y_OFF] = FIX(0.29900) * i;
     rgb_ycc_tab[i+G_Y_OFF] = FIX(0.58700) * i;
     rgb_ycc_tab[i+B_Y_OFF] = FIX(0.11400) * i     + ONE_HALF;
     rgb_ycc_tab[i+R_CB_OFF] = (-FIX(0.16874)) * i;
     rgb_ycc_tab[i+G_CB_OFF] = (-FIX(0.33126)) * i;
     /* We use a rounding fudge-factor of 0.5-epsilon for Cb and Cr.
      * This ensures that the maximum output will round to MAXJSAMPLE
      * not MAXJSAMPLE+1, and thus that we don't have to range-limit.
      */
     rgb_ycc_tab[i+B_CB_OFF] = FIX(0.50000) * i    + CBCR_OFFSET + ONE_HALF-1;
 /*  B=>Cb and R=>Cr tables are the same
     rgb_ycc_tab[i+R_CR_OFF] = FIX(0.50000) * i    + CBCR_OFFSET + ONE_HALF-1;
 */
     rgb_ycc_tab[i+G_CR_OFF] = (-FIX(0.41869)) * i;
     rgb_ycc_tab[i+B_CR_OFF] = (-FIX(0.08131)) * i;
   }
 }


 /*
  * Convert some rows of samples to the JPEG colorspace.
  *
  * Note that we change from the application's interleaved-pixel format
  * to our internal noninterleaved, one-plane-per-component format.
  * The input buffer is therefore three times as wide as the output buffer.
  *
  * A starting row offset is provided only for the output buffer.  The caller
  * can easily adjust the passed input_buf value to accommodate any row
  * offset required on that side.
  */

 METHODDEF void
 rgb_ycc_convert (j_compress_ptr cinfo,
 		 JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
 		 JDIMENSION output_row, int num_rows)
 {
   my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
   register int r, g, b;
   register INT32 * ctab = cconvert->rgb_ycc_tab;
   register JSAMPROW inptr;
   register JSAMPROW outptr0, outptr1, outptr2;
   register JDIMENSION col;
   JDIMENSION num_cols = cinfo->image_width;

   while (--num_rows >= 0) {
     inptr = *input_buf++;
     outptr0 = output_buf[0][output_row];
     outptr1 = output_buf[1][output_row];
     outptr2 = output_buf[2][output_row];
     output_row++;
     for (col = 0; col < num_cols; col++) {
       r = GETJSAMPLE(inptr[RGB_RED]);
       g = GETJSAMPLE(inptr[RGB_GREEN]);
       b = GETJSAMPLE(inptr[RGB_BLUE]);
       inptr += RGB_PIXELSIZE;
       /* If the inputs are 0..MAXJSAMPLE, the outputs of these equations
        * must be too; we do not need an explicit range-limiting operation.
        * Hence the value being shifted is never negative, and we don't
        * need the general RIGHT_SHIFT macro.
        */
       /* Y */
       outptr0[col] = (JSAMPLE)
 		((ctab[r+R_Y_OFF] + ctab[g+G_Y_OFF] + ctab[b+B_Y_OFF])
 		 >> SCALEBITS);
       /* Cb */
       outptr1[col] = (JSAMPLE)
 		((ctab[r+R_CB_OFF] + ctab[g+G_CB_OFF] + ctab[b+B_CB_OFF])
 		 >> SCALEBITS);
       /* Cr */
       outptr2[col] = (JSAMPLE)
 		((ctab[r+R_CR_OFF] + ctab[g+G_CR_OFF] + ctab[b+B_CR_OFF])
 		 >> SCALEBITS);
     }
   }
 }


 /**************** Cases other than RGB -> YCbCr **************/


 /*
  * Convert some rows of samples to the JPEG colorspace.
  * This version handles RGB->grayscale conversion, which is the same
  * as the RGB->Y portion of RGB->YCbCr.
  * We assume rgb_ycc_start has been called (we only use the Y tables).
  */

 METHODDEF void
 rgb_gray_convert (j_compress_ptr cinfo,
 		  JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
 		  JDIMENSION output_row, int num_rows)
 {
   my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
   register int r, g, b;
   register INT32 * ctab = cconvert->rgb_ycc_tab;
   register JSAMPROW inptr;
   register JSAMPROW outptr;
   register JDIMENSION col;
   JDIMENSION num_cols = cinfo->image_width;

   while (--num_rows >= 0) {
     inptr = *input_buf++;
     outptr = output_buf[0][output_row];
     output_row++;
     for (col = 0; col < num_cols; col++) {
       r = GETJSAMPLE(inptr[RGB_RED]);
       g = GETJSAMPLE(inptr[RGB_GREEN]);
       b = GETJSAMPLE(inptr[RGB_BLUE]);
       inptr += RGB_PIXELSIZE;
       /* Y */
       outptr[col] = (JSAMPLE)
 		((ctab[r+R_Y_OFF] + ctab[g+G_Y_OFF] + ctab[b+B_Y_OFF])
 		 >> SCALEBITS);
     }
   }
 }


 /*
  * Convert some rows of samples to the JPEG colorspace.
  * This version handles Adobe-style CMYK->YCCK conversion,
  * where we convert R=1-C, G=1-M, and B=1-Y to YCbCr using the same
  * conversion as above, while passing K (black) unchanged.
  * We assume rgb_ycc_start has been called.
  */

 METHODDEF void
 cmyk_ycck_convert (j_compress_ptr cinfo,
 		   JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
 		   JDIMENSION output_row, int num_rows)
 {
   my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
   register int r, g, b;
   register INT32 * ctab = cconvert->rgb_ycc_tab;
   register JSAMPROW inptr;
   register JSAMPROW outptr0, outptr1, outptr2, outptr3;
   register JDIMENSION col;
   JDIMENSION num_cols = cinfo->image_width;

   while (--num_rows >= 0) {
     inptr = *input_buf++;
     outptr0 = output_buf[0][output_row];
     outptr1 = output_buf[1][output_row];
     outptr2 = output_buf[2][output_row];
     outptr3 = output_buf[3][output_row];
     output_row++;
     for (col = 0; col < num_cols; col++) {
       r = MAXJSAMPLE - GETJSAMPLE(inptr[0]);
       g = MAXJSAMPLE - GETJSAMPLE(inptr[1]);
       b = MAXJSAMPLE - GETJSAMPLE(inptr[2]);
       /* K passes through as-is */
       outptr3[col] = inptr[3];	/* don't need GETJSAMPLE here */
       inptr += 4;
       /* If the inputs are 0..MAXJSAMPLE, the outputs of these equations
        * must be too; we do not need an explicit range-limiting operation.
        * Hence the value being shifted is never negative, and we don't
        * need the general RIGHT_SHIFT macro.
        */
       /* Y */
       outptr0[col] = (JSAMPLE)
 		((ctab[r+R_Y_OFF] + ctab[g+G_Y_OFF] + ctab[b+B_Y_OFF])
 		 >> SCALEBITS);
       /* Cb */
       outptr1[col] = (JSAMPLE)
 		((ctab[r+R_CB_OFF] + ctab[g+G_CB_OFF] + ctab[b+B_CB_OFF])
 		 >> SCALEBITS);
       /* Cr */
       outptr2[col] = (JSAMPLE)
 		((ctab[r+R_CR_OFF] + ctab[g+G_CR_OFF] + ctab[b+B_CR_OFF])
 		 >> SCALEBITS);
     }
   }
 }


 /*
  * Convert some rows of samples to the JPEG colorspace.
  * This version handles grayscale output with no conversion.
  * The source can be either plain grayscale or YCbCr (since Y == gray).
  */

 METHODDEF void
 grayscale_convert (j_compress_ptr cinfo,
 		   JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
 		   JDIMENSION output_row, int num_rows)
 {
   register JSAMPROW inptr;
   register JSAMPROW outptr;
   register JDIMENSION col;
   JDIMENSION num_cols = cinfo->image_width;
   int instride = cinfo->input_components;

   while (--num_rows >= 0) {
     inptr = *input_buf++;
     outptr = output_buf[0][output_row];
     output_row++;
     for (col = 0; col < num_cols; col++) {
       outptr[col] = inptr[0];	/* don't need GETJSAMPLE() here */
       inptr += instride;
     }
   }
 }


 /*
  * Convert some rows of samples to the JPEG colorspace.
  * This version handles multi-component colorspaces without conversion.
  * We assume input_components == num_components.
  */

 METHODDEF void
 null_convert (j_compress_ptr cinfo,
 	      JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
 	      JDIMENSION output_row, int num_rows)
 {
   register JSAMPROW inptr;
   register JSAMPROW outptr;
   register JDIMENSION col;
   register int ci;
   int nc = cinfo->num_components;
   JDIMENSION num_cols = cinfo->image_width;

   while (--num_rows >= 0) {
     /* It seems fastest to make a separate pass for each component. */
     for (ci = 0; ci < nc; ci++) {
       inptr = *input_buf;
       outptr = output_buf[ci][output_row];
       for (col = 0; col < num_cols; col++) {
 	outptr[col] = inptr[ci]; /* don't need GETJSAMPLE() here */
 	inptr += nc;
       }
     }
     input_buf++;
     output_row++;
   }
 }


 /*
  * Empty method for start_pass.
  */

 METHODDEF void
 null_method (j_compress_ptr cinfo)
 {
   /* no work needed */
 }


 /*
  * Module initialization routine for input colorspace conversion.
  */

 GLOBAL void
 jinit_color_converter (j_compress_ptr cinfo)
 {
   my_cconvert_ptr cconvert;

   cconvert = (my_cconvert_ptr)
     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
 				SIZEOF(my_color_converter));
   cinfo->cconvert = (struct jpeg_color_converter *) cconvert;
   /* set start_pass to null method until we find out differently */
   cconvert->pub.start_pass = null_method;

   /* Make sure input_components agrees with in_color_space */
   switch (cinfo->in_color_space) {
   case JCS_GRAYSCALE:
     if (cinfo->input_components != 1)
       ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
     break;

   case JCS_RGB:
 #if RGB_PIXELSIZE != 3
     if (cinfo->input_components != RGB_PIXELSIZE)
       ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
     break;
 #endif /* else share code with YCbCr */

   case JCS_YCbCr:
     if (cinfo->input_components != 3)
       ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
     break;

   case JCS_CMYK:
   case JCS_YCCK:
     if (cinfo->input_components != 4)
       ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
     break;

   default:			/* JCS_UNKNOWN can be anything */
     if (cinfo->input_components < 1)
       ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
     break;
   }

   /* Check num_components, set conversion method based on requested space */
   switch (cinfo->jpeg_color_space) {
   case JCS_GRAYSCALE:
     if (cinfo->num_components != 1)
       ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
     if (cinfo->in_color_space == JCS_GRAYSCALE)
       cconvert->pub.color_convert = grayscale_convert;
     else if (cinfo->in_color_space == JCS_RGB) {
       cconvert->pub.start_pass = rgb_ycc_start;
       cconvert->pub.color_convert = rgb_gray_convert;
     } else if (cinfo->in_color_space == JCS_YCbCr)
       cconvert->pub.color_convert = grayscale_convert;
     else
       ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
     break;

   case JCS_RGB:
     if (cinfo->num_components != 3)
       ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
     if (cinfo->in_color_space == JCS_RGB && RGB_PIXELSIZE == 3)
       cconvert->pub.color_convert = null_convert;
     else
       ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
     break;

   case JCS_YCbCr:
     if (cinfo->num_components != 3)
       ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
     if (cinfo->in_color_space == JCS_RGB) {
       cconvert->pub.start_pass = rgb_ycc_start;
       cconvert->pub.color_convert = rgb_ycc_convert;
     } else if (cinfo->in_color_space == JCS_YCbCr)
       cconvert->pub.color_convert = null_convert;
     else
       ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
     break;

   case JCS_CMYK:
     if (cinfo->num_components != 4)
       ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
     if (cinfo->in_color_space == JCS_CMYK)
       cconvert->pub.color_convert = null_convert;
     else
       ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
     break;

   case JCS_YCCK:
     if (cinfo->num_components != 4)
       ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
     if (cinfo->in_color_space == JCS_CMYK) {
       cconvert->pub.start_pass = rgb_ycc_start;
       cconvert->pub.color_convert = cmyk_ycck_convert;
     } else if (cinfo->in_color_space == JCS_YCCK)
       cconvert->pub.color_convert = null_convert;
     else
       ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
     break;

   default:			/* allow null conversion of JCS_UNKNOWN */
     if (cinfo->jpeg_color_space != cinfo->in_color_space ||
 	cinfo->num_components != cinfo->input_components)
       ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
     cconvert->pub.color_convert = null_convert;
     break;
   }
 }
	/*
	* jccolor.c
	*
	* Copyright (C) 1991-1994, Thomas G. Lane.
	* This file is part of the Independent JPEG Group's software.
	* For conditions of distribution and use, see the accompanying README file.
	*
	* This file contains input colorspace conversion routines.
	*/

	#define JPEG_INTERNALS
	#include "jinclude.h"
	#include "jpeglib.h"


	/* Private subobject */

	typedef struct {
	struct jpeg_color_converter pub; /* public fields */

	/* Private state for RGB->YCC conversion */
	INT32 * rgb_ycc_tab; /* => table for RGB to YCbCr conversion */
	} my_color_converter;

	typedef my_color_converter * my_cconvert_ptr;


	/************** RGB -> YCbCr conversion: most common case ************/

	/*
	* YCbCr is defined per CCIR 601-1, except that Cb and Cr are
	* normalized to the range 0..MAXJSAMPLE rather than -0.5 .. 0.5.
	* The conversion equations to be implemented are therefore
	* Y = 0.29900 * R + 0.58700 * G + 0.11400 * B
	* Cb = -0.16874 * R - 0.33126 * G + 0.50000 * B + CENTERJSAMPLE
	* Cr = 0.50000 * R - 0.41869 * G - 0.08131 * B + CENTERJSAMPLE
	* (These numbers are derived from TIFF 6.0 section 21, dated 3-June-92.)
	* Note: older versions of the IJG code used a zero offset of MAXJSAMPLE/2,
	* rather than CENTERJSAMPLE, for Cb and Cr. This gave equal positive and
	* negative swings for Cb/Cr, but meant that grayscale values (Cb=Cr=0)
	* were not represented exactly. Now we sacrifice exact representation of
	* maximum red and maximum blue in order to get exact grayscales.
	*
	* To avoid floating-point arithmetic, we represent the fractional constants
	* as integers scaled up by 2^16 (about 4 digits precision); we have to divide
	* the products by 2^16, with appropriate rounding, to get the correct answer.
	*
	* For even more speed, we avoid doing any multiplications in the inner loop
	* by precalculating the constants times R,G,B for all possible values.
	* For 8-bit JSAMPLEs this is very reasonable (only 256 entries per table);
	* for 12-bit samples it is still acceptable. It's not very reasonable for
	* 16-bit samples, but if you want lossless storage you shouldn't be changing
	* colorspace anyway.
	* The CENTERJSAMPLE offsets and the rounding fudge-factor of 0.5 are included
	* in the tables to save adding them separately in the inner loop.
	*/

	#define SCALEBITS 16 /* speediest right-shift on some machines */
	#define CBCR_OFFSET ((INT32) CENTERJSAMPLE << SCALEBITS)
	#define ONE_HALF ((INT32) 1 << (SCALEBITS-1))
	#define FIX(x) ((INT32) ((x) * (1L<<SCALEBITS) + 0.5))

	/* We allocate one big table and divide it up into eight parts, instead of
	* doing eight alloc_small requests. This lets us use a single table base
	* address, which can be held in a register in the inner loops on many
	* machines (more than can hold all eight addresses, anyway).
	*/

	#define R_Y_OFF 0 /* offset to R => Y section */
	#define G_Y_OFF (1(MAXJSAMPLE+1)) / offset to G => Y section */
	#define B_Y_OFF (2(MAXJSAMPLE+1)) / etc. */
	#define R_CB_OFF (3*(MAXJSAMPLE+1))
	#define G_CB_OFF (4*(MAXJSAMPLE+1))
	#define B_CB_OFF (5*(MAXJSAMPLE+1))
	#define R_CR_OFF B_CB_OFF /* B=>Cb, R=>Cr are the same */
	#define G_CR_OFF (6*(MAXJSAMPLE+1))
	#define B_CR_OFF (7*(MAXJSAMPLE+1))
	#define TABLE_SIZE (8*(MAXJSAMPLE+1))


	/*
	* Initialize for RGB->YCC colorspace conversion.
	*/

	METHODDEF void
	rgb_ycc_start (j_compress_ptr cinfo)
	{
	my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
	INT32 * rgb_ycc_tab;
	INT32 i;

	/* Allocate and fill in the conversion tables. */
	cconvert->rgb_ycc_tab = rgb_ycc_tab = (INT32 *)
	(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
	(TABLE_SIZE * SIZEOF(INT32)));

	for (i = 0; i <= MAXJSAMPLE; i++) {
	rgb_ycc_tab[i+R_Y_OFF] = FIX(0.29900) * i;
	rgb_ycc_tab[i+G_Y_OFF] = FIX(0.58700) * i;
	rgb_ycc_tab[i+B_Y_OFF] = FIX(0.11400) * i + ONE_HALF;
	rgb_ycc_tab[i+R_CB_OFF] = (-FIX(0.16874)) * i;
	rgb_ycc_tab[i+G_CB_OFF] = (-FIX(0.33126)) * i;
	/* We use a rounding fudge-factor of 0.5-epsilon for Cb and Cr.
	* This ensures that the maximum output will round to MAXJSAMPLE
	* not MAXJSAMPLE+1, and thus that we don't have to range-limit.
	*/
	rgb_ycc_tab[i+B_CB_OFF] = FIX(0.50000) * i + CBCR_OFFSET + ONE_HALF-1;
	/* B=>Cb and R=>Cr tables are the same
	rgb_ycc_tab[i+R_CR_OFF] = FIX(0.50000) * i + CBCR_OFFSET + ONE_HALF-1;
	*/
	rgb_ycc_tab[i+G_CR_OFF] = (-FIX(0.41869)) * i;
	rgb_ycc_tab[i+B_CR_OFF] = (-FIX(0.08131)) * i;
	}
	}


	/*
	* Convert some rows of samples to the JPEG colorspace.
	*
	* Note that we change from the application's interleaved-pixel format
	* to our internal noninterleaved, one-plane-per-component format.
	* The input buffer is therefore three times as wide as the output buffer.
	*
	* A starting row offset is provided only for the output buffer. The caller
	* can easily adjust the passed input_buf value to accommodate any row
	* offset required on that side.
	*/

	METHODDEF void
	rgb_ycc_convert (j_compress_ptr cinfo,
	JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
	JDIMENSION output_row, int num_rows)
	{
	my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
	register int r, g, b;
	register INT32 * ctab = cconvert->rgb_ycc_tab;
	register JSAMPROW inptr;
	register JSAMPROW outptr0, outptr1, outptr2;
	register JDIMENSION col;
	JDIMENSION num_cols = cinfo->image_width;

	while (--num_rows >= 0) {
	inptr = *input_buf++;
	outptr0 = output_buf[0][output_row];
	outptr1 = output_buf[1][output_row];
	outptr2 = output_buf[2][output_row];
	output_row++;
	for (col = 0; col < num_cols; col++) {
	r = GETJSAMPLE(inptr[RGB_RED]);
	g = GETJSAMPLE(inptr[RGB_GREEN]);
	b = GETJSAMPLE(inptr[RGB_BLUE]);
	inptr += RGB_PIXELSIZE;
	/* If the inputs are 0..MAXJSAMPLE, the outputs of these equations
	* must be too; we do not need an explicit range-limiting operation.
	* Hence the value being shifted is never negative, and we don't
	* need the general RIGHT_SHIFT macro.
	*/
	/* Y */
	outptr0[col] = (JSAMPLE)
	((ctab[r+R_Y_OFF] + ctab[g+G_Y_OFF] + ctab[b+B_Y_OFF])
	>> SCALEBITS);
	/* Cb */
	outptr1[col] = (JSAMPLE)
	((ctab[r+R_CB_OFF] + ctab[g+G_CB_OFF] + ctab[b+B_CB_OFF])
	>> SCALEBITS);
	/* Cr */
	outptr2[col] = (JSAMPLE)
	((ctab[r+R_CR_OFF] + ctab[g+G_CR_OFF] + ctab[b+B_CR_OFF])
	>> SCALEBITS);
	}
	}
	}


	/************** Cases other than RGB -> YCbCr ************/


	/*
	* Convert some rows of samples to the JPEG colorspace.
	* This version handles RGB->grayscale conversion, which is the same
	* as the RGB->Y portion of RGB->YCbCr.
	* We assume rgb_ycc_start has been called (we only use the Y tables).
	*/

	METHODDEF void
	rgb_gray_convert (j_compress_ptr cinfo,
	JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
	JDIMENSION output_row, int num_rows)
	{
	my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
	register int r, g, b;
	register INT32 * ctab = cconvert->rgb_ycc_tab;
	register JSAMPROW inptr;
	register JSAMPROW outptr;
	register JDIMENSION col;
	JDIMENSION num_cols = cinfo->image_width;

	while (--num_rows >= 0) {
	inptr = *input_buf++;
	outptr = output_buf[0][output_row];
	output_row++;
	for (col = 0; col < num_cols; col++) {
	r = GETJSAMPLE(inptr[RGB_RED]);
	g = GETJSAMPLE(inptr[RGB_GREEN]);
	b = GETJSAMPLE(inptr[RGB_BLUE]);
	inptr += RGB_PIXELSIZE;
	/* Y */
	outptr[col] = (JSAMPLE)
	((ctab[r+R_Y_OFF] + ctab[g+G_Y_OFF] + ctab[b+B_Y_OFF])
	>> SCALEBITS);
	}
	}
	}


	/*
	* Convert some rows of samples to the JPEG colorspace.
	* This version handles Adobe-style CMYK->YCCK conversion,
	* where we convert R=1-C, G=1-M, and B=1-Y to YCbCr using the same
	* conversion as above, while passing K (black) unchanged.
	* We assume rgb_ycc_start has been called.
	*/

	METHODDEF void
	cmyk_ycck_convert (j_compress_ptr cinfo,
	JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
	JDIMENSION output_row, int num_rows)
	{
	my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
	register int r, g, b;
	register INT32 * ctab = cconvert->rgb_ycc_tab;
	register JSAMPROW inptr;
	register JSAMPROW outptr0, outptr1, outptr2, outptr3;
	register JDIMENSION col;
	JDIMENSION num_cols = cinfo->image_width;

	while (--num_rows >= 0) {
	inptr = *input_buf++;
	outptr0 = output_buf[0][output_row];
	outptr1 = output_buf[1][output_row];
	outptr2 = output_buf[2][output_row];
	outptr3 = output_buf[3][output_row];
	output_row++;
	for (col = 0; col < num_cols; col++) {
	r = MAXJSAMPLE - GETJSAMPLE(inptr[0]);
	g = MAXJSAMPLE - GETJSAMPLE(inptr[1]);
	b = MAXJSAMPLE - GETJSAMPLE(inptr[2]);
	/* K passes through as-is */
	outptr3[col] = inptr[3]; /* don't need GETJSAMPLE here */
	inptr += 4;
	/* If the inputs are 0..MAXJSAMPLE, the outputs of these equations
	* must be too; we do not need an explicit range-limiting operation.
	* Hence the value being shifted is never negative, and we don't
	* need the general RIGHT_SHIFT macro.
	*/
	/* Y */
	outptr0[col] = (JSAMPLE)
	((ctab[r+R_Y_OFF] + ctab[g+G_Y_OFF] + ctab[b+B_Y_OFF])
	>> SCALEBITS);
	/* Cb */
	outptr1[col] = (JSAMPLE)
	((ctab[r+R_CB_OFF] + ctab[g+G_CB_OFF] + ctab[b+B_CB_OFF])
	>> SCALEBITS);
	/* Cr */
	outptr2[col] = (JSAMPLE)
	((ctab[r+R_CR_OFF] + ctab[g+G_CR_OFF] + ctab[b+B_CR_OFF])
	>> SCALEBITS);
	}
	}
	}


	/*
	* Convert some rows of samples to the JPEG colorspace.
	* This version handles grayscale output with no conversion.
	* The source can be either plain grayscale or YCbCr (since Y == gray).
	*/

	METHODDEF void
	grayscale_convert (j_compress_ptr cinfo,
	JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
	JDIMENSION output_row, int num_rows)
	{
	register JSAMPROW inptr;
	register JSAMPROW outptr;
	register JDIMENSION col;
	JDIMENSION num_cols = cinfo->image_width;
	int instride = cinfo->input_components;

	while (--num_rows >= 0) {
	inptr = *input_buf++;
	outptr = output_buf[0][output_row];
	output_row++;
	for (col = 0; col < num_cols; col++) {
	outptr[col] = inptr[0]; /* don't need GETJSAMPLE() here */
	inptr += instride;
	}
	}
	}


	/*
	* Convert some rows of samples to the JPEG colorspace.
	* This version handles multi-component colorspaces without conversion.
	* We assume input_components == num_components.
	*/

	METHODDEF void
	null_convert (j_compress_ptr cinfo,
	JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
	JDIMENSION output_row, int num_rows)
	{
	register JSAMPROW inptr;
	register JSAMPROW outptr;
	register JDIMENSION col;
	register int ci;
	int nc = cinfo->num_components;
	JDIMENSION num_cols = cinfo->image_width;

	while (--num_rows >= 0) {
	/* It seems fastest to make a separate pass for each component. */
	for (ci = 0; ci < nc; ci++) {
	inptr = *input_buf;
	outptr = output_buf[ci][output_row];
	for (col = 0; col < num_cols; col++) {
	outptr[col] = inptr[ci]; /* don't need GETJSAMPLE() here */
	inptr += nc;
	}
	}
	input_buf++;
	output_row++;
	}
	}


	/*
	* Empty method for start_pass.
	*/

	METHODDEF void
	null_method (j_compress_ptr cinfo)
	{
	/* no work needed */
	}


	/*
	* Module initialization routine for input colorspace conversion.
	*/

	GLOBAL void
	jinit_color_converter (j_compress_ptr cinfo)
	{
	my_cconvert_ptr cconvert;

	cconvert = (my_cconvert_ptr)
	(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
	SIZEOF(my_color_converter));
	cinfo->cconvert = (struct jpeg_color_converter *) cconvert;
	/* set start_pass to null method until we find out differently */
	cconvert->pub.start_pass = null_method;

	/* Make sure input_components agrees with in_color_space */
	switch (cinfo->in_color_space) {
	case JCS_GRAYSCALE:
	if (cinfo->input_components != 1)
	ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
	break;

	case JCS_RGB:
	#if RGB_PIXELSIZE != 3
	if (cinfo->input_components != RGB_PIXELSIZE)
	ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
	break;
	#endif /* else share code with YCbCr */

	case JCS_YCbCr:
	if (cinfo->input_components != 3)
	ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
	break;

	case JCS_CMYK:
	case JCS_YCCK:
	if (cinfo->input_components != 4)
	ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
	break;

	default: /* JCS_UNKNOWN can be anything */
	if (cinfo->input_components < 1)
	ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
	break;
	}

	/* Check num_components, set conversion method based on requested space */
	switch (cinfo->jpeg_color_space) {
	case JCS_GRAYSCALE:
	if (cinfo->num_components != 1)
	ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
	if (cinfo->in_color_space == JCS_GRAYSCALE)
	cconvert->pub.color_convert = grayscale_convert;
	else if (cinfo->in_color_space == JCS_RGB) {
	cconvert->pub.start_pass = rgb_ycc_start;
	cconvert->pub.color_convert = rgb_gray_convert;
	} else if (cinfo->in_color_space == JCS_YCbCr)
	cconvert->pub.color_convert = grayscale_convert;
	else
	ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
	break;

	case JCS_RGB:
	if (cinfo->num_components != 3)
	ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
	if (cinfo->in_color_space == JCS_RGB && RGB_PIXELSIZE == 3)
	cconvert->pub.color_convert = null_convert;
	else
	ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
	break;

	case JCS_YCbCr:
	if (cinfo->num_components != 3)
	ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
	if (cinfo->in_color_space == JCS_RGB) {
	cconvert->pub.start_pass = rgb_ycc_start;
	cconvert->pub.color_convert = rgb_ycc_convert;
	} else if (cinfo->in_color_space == JCS_YCbCr)
	cconvert->pub.color_convert = null_convert;
	else
	ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
	break;

	case JCS_CMYK:
	if (cinfo->num_components != 4)
	ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
	if (cinfo->in_color_space == JCS_CMYK)
	cconvert->pub.color_convert = null_convert;
	else
	ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
	break;

	case JCS_YCCK:
	if (cinfo->num_components != 4)
	ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
	if (cinfo->in_color_space == JCS_CMYK) {
	cconvert->pub.start_pass = rgb_ycc_start;
	cconvert->pub.color_convert = cmyk_ycck_convert;
	} else if (cinfo->in_color_space == JCS_YCCK)
	cconvert->pub.color_convert = null_convert;
	else
	ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
	break;

	default: /* allow null conversion of JCS_UNKNOWN */
	if (cinfo->jpeg_color_space != cinfo->in_color_space \|\|
	cinfo->num_components != cinfo->input_components)
	ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
	cconvert->pub.color_convert = null_convert;
	break;
	}
	}