# dlib C++ Library - jccolor.c

    /*
     * jccolor.c
     *
     * Copyright (C) 1991-1996, Thomas G. Lane.
     * Modified 2011 by Guido Vollbeding.
     * 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.
     * No colorspace conversion, but change from interleaved
     * to separate-planes representation.
     */

    METHODDEF(void)
    rgb_convert (j_compress_ptr cinfo,
    	     JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
    	     JDIMENSION output_row, int num_rows)
    {
      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++) {
          /* We can dispense with GETJSAMPLE() here */
          outptr0[col] = inptr[RGB_RED];
          outptr1[col] = inptr[RGB_GREEN];
          outptr2[col] = inptr[RGB_BLUE];
          inptr += RGB_PIXELSIZE;
        }
      }
    }

    /*
     * 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 (cinfo->input_components != RGB_PIXELSIZE)
          ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
        break;

      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 ||
    	cinfo->in_color_space == JCS_YCbCr)
          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
          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)
          cconvert->pub.color_convert = rgb_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;
      }
    }