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jccolor.c
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00001 /*
00002  * jccolor.c
00003  *
00004  * Copyright (C) 1991-1996, Thomas G. Lane.
00005  * This file is part of the Independent JPEG Group's software.
00006  * For conditions of distribution and use, see the accompanying README file.
00007  *
00008  * This file contains input colorspace conversion routines.
00009  */
00010 
00011 #define JPEG_INTERNALS
00012 #include "jinclude.h"
00013 #include "jpeglib.h"
00014 
00015 
00016 /* Private subobject */
00017 
00018 typedef struct {
00019   struct jpeg_color_converter pub; /* public fields */
00020 
00021   /* Private state for RGB->YCC conversion */
00022   INT32 * rgb_ycc_tab;             /* => table for RGB to YCbCr conversion */
00023 } my_color_converter;
00024 
00025 typedef my_color_converter * my_cconvert_ptr;
00026 
00027 
00028 /**************** RGB -> YCbCr conversion: most common case **************/
00029 
00030 /*
00031  * YCbCr is defined per CCIR 601-1, except that Cb and Cr are
00032  * normalized to the range 0..MAXJSAMPLE rather than -0.5 .. 0.5.
00033  * The conversion equations to be implemented are therefore
00034  *     Y  =  0.29900 * R + 0.58700 * G + 0.11400 * B
00035  *     Cb = -0.16874 * R - 0.33126 * G + 0.50000 * B  + CENTERJSAMPLE
00036  *     Cr =  0.50000 * R - 0.41869 * G - 0.08131 * B  + CENTERJSAMPLE
00037  * (These numbers are derived from TIFF 6.0 section 21, dated 3-June-92.)
00038  * Note: older versions of the IJG code used a zero offset of MAXJSAMPLE/2,
00039  * rather than CENTERJSAMPLE, for Cb and Cr.  This gave equal positive and
00040  * negative swings for Cb/Cr, but meant that grayscale values (Cb=Cr=0)
00041  * were not represented exactly.  Now we sacrifice exact representation of
00042  * maximum red and maximum blue in order to get exact grayscales.
00043  *
00044  * To avoid floating-point arithmetic, we represent the fractional constants
00045  * as integers scaled up by 2^16 (about 4 digits precision); we have to divide
00046  * the products by 2^16, with appropriate rounding, to get the correct answer.
00047  *
00048  * For even more speed, we avoid doing any multiplications in the inner loop
00049  * by precalculating the constants times R,G,B for all possible values.
00050  * For 8-bit JSAMPLEs this is very reasonable (only 256 entries per table);
00051  * for 12-bit samples it is still acceptable.  It's not very reasonable for
00052  * 16-bit samples, but if you want lossless storage you shouldn't be changing
00053  * colorspace anyway.
00054  * The CENTERJSAMPLE offsets and the rounding fudge-factor of 0.5 are included
00055  * in the tables to save adding them separately in the inner loop.
00056  */
00057 
00058 #define SCALEBITS    16     /* speediest right-shift on some machines */
00059 #define CBCR_OFFSET  ((INT32) CENTERJSAMPLE << SCALEBITS)
00060 #define ONE_HALF     ((INT32) 1 << (SCALEBITS-1))
00061 #define FIX(x)              ((INT32) ((x) * (1L<<SCALEBITS) + 0.5))
00062 
00063 /* We allocate one big table and divide it up into eight parts, instead of
00064  * doing eight alloc_small requests.  This lets us use a single table base
00065  * address, which can be held in a register in the inner loops on many
00066  * machines (more than can hold all eight addresses, anyway).
00067  */
00068 
00069 #define R_Y_OFF             0                    /* offset to R => Y section */
00070 #define G_Y_OFF             (1*(MAXJSAMPLE+1))   /* offset to G => Y section */
00071 #define B_Y_OFF             (2*(MAXJSAMPLE+1))   /* etc. */
00072 #define R_CB_OFF     (3*(MAXJSAMPLE+1))
00073 #define G_CB_OFF     (4*(MAXJSAMPLE+1))
00074 #define B_CB_OFF     (5*(MAXJSAMPLE+1))
00075 #define R_CR_OFF     B_CB_OFF             /* B=>Cb, R=>Cr are the same */
00076 #define G_CR_OFF     (6*(MAXJSAMPLE+1))
00077 #define B_CR_OFF     (7*(MAXJSAMPLE+1))
00078 #define TABLE_SIZE   (8*(MAXJSAMPLE+1))
00079 
00080 
00081 /*
00082  * Initialize for RGB->YCC colorspace conversion.
00083  */
00084 
00085 METHODDEF(void)
00086 rgb_ycc_start (j_compress_ptr cinfo)
00087 {
00088   my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
00089   INT32 * rgb_ycc_tab;
00090   INT32 i;
00091 
00092   /* Allocate and fill in the conversion tables. */
00093   cconvert->rgb_ycc_tab = rgb_ycc_tab = (INT32 *)
00094     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
00095                             (TABLE_SIZE * SIZEOF(INT32)));
00096 
00097   for (i = 0; i <= MAXJSAMPLE; i++) {
00098     rgb_ycc_tab[i+R_Y_OFF] = FIX(0.29900) * i;
00099     rgb_ycc_tab[i+G_Y_OFF] = FIX(0.58700) * i;
00100     rgb_ycc_tab[i+B_Y_OFF] = FIX(0.11400) * i     + ONE_HALF;
00101     rgb_ycc_tab[i+R_CB_OFF] = (-FIX(0.16874)) * i;
00102     rgb_ycc_tab[i+G_CB_OFF] = (-FIX(0.33126)) * i;
00103     /* We use a rounding fudge-factor of 0.5-epsilon for Cb and Cr.
00104      * This ensures that the maximum output will round to MAXJSAMPLE
00105      * not MAXJSAMPLE+1, and thus that we don't have to range-limit.
00106      */
00107     rgb_ycc_tab[i+B_CB_OFF] = FIX(0.50000) * i    + CBCR_OFFSET + ONE_HALF-1;
00108 /*  B=>Cb and R=>Cr tables are the same
00109     rgb_ycc_tab[i+R_CR_OFF] = FIX(0.50000) * i    + CBCR_OFFSET + ONE_HALF-1;
00110 */
00111     rgb_ycc_tab[i+G_CR_OFF] = (-FIX(0.41869)) * i;
00112     rgb_ycc_tab[i+B_CR_OFF] = (-FIX(0.08131)) * i;
00113   }
00114 }
00115 
00116 
00117 /*
00118  * Convert some rows of samples to the JPEG colorspace.
00119  *
00120  * Note that we change from the application's interleaved-pixel format
00121  * to our internal noninterleaved, one-plane-per-component format.
00122  * The input buffer is therefore three times as wide as the output buffer.
00123  *
00124  * A starting row offset is provided only for the output buffer.  The caller
00125  * can easily adjust the passed input_buf value to accommodate any row
00126  * offset required on that side.
00127  */
00128 
00129 METHODDEF(void)
00130 rgb_ycc_convert (j_compress_ptr cinfo,
00131                JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
00132                JDIMENSION output_row, int num_rows)
00133 {
00134   my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
00135   register int r, g, b;
00136   register INT32 * ctab = cconvert->rgb_ycc_tab;
00137   register JSAMPROW inptr;
00138   register JSAMPROW outptr0, outptr1, outptr2;
00139   register JDIMENSION col;
00140   JDIMENSION num_cols = cinfo->image_width;
00141 
00142   while (--num_rows >= 0) {
00143     inptr = *input_buf++;
00144     outptr0 = output_buf[0][output_row];
00145     outptr1 = output_buf[1][output_row];
00146     outptr2 = output_buf[2][output_row];
00147     output_row++;
00148     for (col = 0; col < num_cols; col++) {
00149       r = GETJSAMPLE(inptr[RGB_RED]);
00150       g = GETJSAMPLE(inptr[RGB_GREEN]);
00151       b = GETJSAMPLE(inptr[RGB_BLUE]);
00152       inptr += RGB_PIXELSIZE;
00153       /* If the inputs are 0..MAXJSAMPLE, the outputs of these equations
00154        * must be too; we do not need an explicit range-limiting operation.
00155        * Hence the value being shifted is never negative, and we don't
00156        * need the general RIGHT_SHIFT macro.
00157        */
00158       /* Y */
00159       outptr0[col] = (JSAMPLE)
00160               ((ctab[r+R_Y_OFF] + ctab[g+G_Y_OFF] + ctab[b+B_Y_OFF])
00161                >> SCALEBITS);
00162       /* Cb */
00163       outptr1[col] = (JSAMPLE)
00164               ((ctab[r+R_CB_OFF] + ctab[g+G_CB_OFF] + ctab[b+B_CB_OFF])
00165                >> SCALEBITS);
00166       /* Cr */
00167       outptr2[col] = (JSAMPLE)
00168               ((ctab[r+R_CR_OFF] + ctab[g+G_CR_OFF] + ctab[b+B_CR_OFF])
00169                >> SCALEBITS);
00170     }
00171   }
00172 }
00173 
00174 
00175 /**************** Cases other than RGB -> YCbCr **************/
00176 
00177 
00178 /*
00179  * Convert some rows of samples to the JPEG colorspace.
00180  * This version handles RGB->grayscale conversion, which is the same
00181  * as the RGB->Y portion of RGB->YCbCr.
00182  * We assume rgb_ycc_start has been called (we only use the Y tables).
00183  */
00184 
00185 METHODDEF(void)
00186 rgb_gray_convert (j_compress_ptr cinfo,
00187                 JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
00188                 JDIMENSION output_row, int num_rows)
00189 {
00190   my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
00191   register int r, g, b;
00192   register INT32 * ctab = cconvert->rgb_ycc_tab;
00193   register JSAMPROW inptr;
00194   register JSAMPROW outptr;
00195   register JDIMENSION col;
00196   JDIMENSION num_cols = cinfo->image_width;
00197 
00198   while (--num_rows >= 0) {
00199     inptr = *input_buf++;
00200     outptr = output_buf[0][output_row];
00201     output_row++;
00202     for (col = 0; col < num_cols; col++) {
00203       r = GETJSAMPLE(inptr[RGB_RED]);
00204       g = GETJSAMPLE(inptr[RGB_GREEN]);
00205       b = GETJSAMPLE(inptr[RGB_BLUE]);
00206       inptr += RGB_PIXELSIZE;
00207       /* Y */
00208       outptr[col] = (JSAMPLE)
00209               ((ctab[r+R_Y_OFF] + ctab[g+G_Y_OFF] + ctab[b+B_Y_OFF])
00210                >> SCALEBITS);
00211     }
00212   }
00213 }
00214 
00215 
00216 /*
00217  * Convert some rows of samples to the JPEG colorspace.
00218  * This version handles Adobe-style CMYK->YCCK conversion,
00219  * where we convert R=1-C, G=1-M, and B=1-Y to YCbCr using the same
00220  * conversion as above, while passing K (black) unchanged.
00221  * We assume rgb_ycc_start has been called.
00222  */
00223 
00224 METHODDEF(void)
00225 cmyk_ycck_convert (j_compress_ptr cinfo,
00226                  JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
00227                  JDIMENSION output_row, int num_rows)
00228 {
00229   my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
00230   register int r, g, b;
00231   register INT32 * ctab = cconvert->rgb_ycc_tab;
00232   register JSAMPROW inptr;
00233   register JSAMPROW outptr0, outptr1, outptr2, outptr3;
00234   register JDIMENSION col;
00235   JDIMENSION num_cols = cinfo->image_width;
00236 
00237   while (--num_rows >= 0) {
00238     inptr = *input_buf++;
00239     outptr0 = output_buf[0][output_row];
00240     outptr1 = output_buf[1][output_row];
00241     outptr2 = output_buf[2][output_row];
00242     outptr3 = output_buf[3][output_row];
00243     output_row++;
00244     for (col = 0; col < num_cols; col++) {
00245       r = MAXJSAMPLE - GETJSAMPLE(inptr[0]);
00246       g = MAXJSAMPLE - GETJSAMPLE(inptr[1]);
00247       b = MAXJSAMPLE - GETJSAMPLE(inptr[2]);
00248       /* K passes through as-is */
00249       outptr3[col] = inptr[3];     /* don't need GETJSAMPLE here */
00250       inptr += 4;
00251       /* If the inputs are 0..MAXJSAMPLE, the outputs of these equations
00252        * must be too; we do not need an explicit range-limiting operation.
00253        * Hence the value being shifted is never negative, and we don't
00254        * need the general RIGHT_SHIFT macro.
00255        */
00256       /* Y */
00257       outptr0[col] = (JSAMPLE)
00258               ((ctab[r+R_Y_OFF] + ctab[g+G_Y_OFF] + ctab[b+B_Y_OFF])
00259                >> SCALEBITS);
00260       /* Cb */
00261       outptr1[col] = (JSAMPLE)
00262               ((ctab[r+R_CB_OFF] + ctab[g+G_CB_OFF] + ctab[b+B_CB_OFF])
00263                >> SCALEBITS);
00264       /* Cr */
00265       outptr2[col] = (JSAMPLE)
00266               ((ctab[r+R_CR_OFF] + ctab[g+G_CR_OFF] + ctab[b+B_CR_OFF])
00267                >> SCALEBITS);
00268     }
00269   }
00270 }
00271 
00272 
00273 /*
00274  * Convert some rows of samples to the JPEG colorspace.
00275  * This version handles grayscale output with no conversion.
00276  * The source can be either plain grayscale or YCbCr (since Y == gray).
00277  */
00278 
00279 METHODDEF(void)
00280 grayscale_convert (j_compress_ptr cinfo,
00281                  JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
00282                  JDIMENSION output_row, int num_rows)
00283 {
00284   register JSAMPROW inptr;
00285   register JSAMPROW outptr;
00286   register JDIMENSION col;
00287   JDIMENSION num_cols = cinfo->image_width;
00288   int instride = cinfo->input_components;
00289 
00290   while (--num_rows >= 0) {
00291     inptr = *input_buf++;
00292     outptr = output_buf[0][output_row];
00293     output_row++;
00294     for (col = 0; col < num_cols; col++) {
00295       outptr[col] = inptr[0];      /* don't need GETJSAMPLE() here */
00296       inptr += instride;
00297     }
00298   }
00299 }
00300 
00301 
00302 /*
00303  * Convert some rows of samples to the JPEG colorspace.
00304  * This version handles multi-component colorspaces without conversion.
00305  * We assume input_components == num_components.
00306  */
00307 
00308 METHODDEF(void)
00309 null_convert (j_compress_ptr cinfo,
00310              JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
00311              JDIMENSION output_row, int num_rows)
00312 {
00313   register JSAMPROW inptr;
00314   register JSAMPROW outptr;
00315   register JDIMENSION col;
00316   register int ci;
00317   int nc = cinfo->num_components;
00318   JDIMENSION num_cols = cinfo->image_width;
00319 
00320   while (--num_rows >= 0) {
00321     /* It seems fastest to make a separate pass for each component. */
00322     for (ci = 0; ci < nc; ci++) {
00323       inptr = *input_buf;
00324       outptr = output_buf[ci][output_row];
00325       for (col = 0; col < num_cols; col++) {
00326        outptr[col] = inptr[ci]; /* don't need GETJSAMPLE() here */
00327        inptr += nc;
00328       }
00329     }
00330     input_buf++;
00331     output_row++;
00332   }
00333 }
00334 
00335 
00336 /*
00337  * Empty method for start_pass.
00338  */
00339 
00340 METHODDEF(void)
00341 null_method (j_compress_ptr cinfo)
00342 {
00343   /* no work needed */
00344 }
00345 
00346 
00347 /*
00348  * Module initialization routine for input colorspace conversion.
00349  */
00350 
00351 GLOBAL(void)
00352 jinit_color_converter (j_compress_ptr cinfo)
00353 {
00354   my_cconvert_ptr cconvert;
00355 
00356   cconvert = (my_cconvert_ptr)
00357     (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
00358                             SIZEOF(my_color_converter));
00359   cinfo->cconvert = (struct jpeg_color_converter *) cconvert;
00360   /* set start_pass to null method until we find out differently */
00361   cconvert->pub.start_pass = null_method;
00362 
00363   /* Make sure input_components agrees with in_color_space */
00364   switch (cinfo->in_color_space) {
00365   case JCS_GRAYSCALE:
00366     if (cinfo->input_components != 1)
00367       ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
00368     break;
00369 
00370   case JCS_RGB:
00371 #if RGB_PIXELSIZE != 3
00372     if (cinfo->input_components != RGB_PIXELSIZE)
00373       ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
00374     break;
00375 #endif /* else share code with YCbCr */
00376 
00377   case JCS_YCbCr:
00378     if (cinfo->input_components != 3)
00379       ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
00380     break;
00381 
00382   case JCS_CMYK:
00383   case JCS_YCCK:
00384     if (cinfo->input_components != 4)
00385       ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
00386     break;
00387 
00388   default:                  /* JCS_UNKNOWN can be anything */
00389     if (cinfo->input_components < 1)
00390       ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
00391     break;
00392   }
00393 
00394   /* Check num_components, set conversion method based on requested space */
00395   switch (cinfo->jpeg_color_space) {
00396   case JCS_GRAYSCALE:
00397     if (cinfo->num_components != 1)
00398       ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
00399     if (cinfo->in_color_space == JCS_GRAYSCALE)
00400       cconvert->pub.color_convert = grayscale_convert;
00401     else if (cinfo->in_color_space == JCS_RGB) {
00402       cconvert->pub.start_pass = rgb_ycc_start;
00403       cconvert->pub.color_convert = rgb_gray_convert;
00404     } else if (cinfo->in_color_space == JCS_YCbCr)
00405       cconvert->pub.color_convert = grayscale_convert;
00406     else
00407       ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
00408     break;
00409 
00410   case JCS_RGB:
00411     if (cinfo->num_components != 3)
00412       ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
00413     if (cinfo->in_color_space == JCS_RGB && RGB_PIXELSIZE == 3)
00414       cconvert->pub.color_convert = null_convert;
00415     else
00416       ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
00417     break;
00418 
00419   case JCS_YCbCr:
00420     if (cinfo->num_components != 3)
00421       ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
00422     if (cinfo->in_color_space == JCS_RGB) {
00423       cconvert->pub.start_pass = rgb_ycc_start;
00424       cconvert->pub.color_convert = rgb_ycc_convert;
00425     } else if (cinfo->in_color_space == JCS_YCbCr)
00426       cconvert->pub.color_convert = null_convert;
00427     else
00428       ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
00429     break;
00430 
00431   case JCS_CMYK:
00432     if (cinfo->num_components != 4)
00433       ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
00434     if (cinfo->in_color_space == JCS_CMYK)
00435       cconvert->pub.color_convert = null_convert;
00436     else
00437       ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
00438     break;
00439 
00440   case JCS_YCCK:
00441     if (cinfo->num_components != 4)
00442       ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
00443     if (cinfo->in_color_space == JCS_CMYK) {
00444       cconvert->pub.start_pass = rgb_ycc_start;
00445       cconvert->pub.color_convert = cmyk_ycck_convert;
00446     } else if (cinfo->in_color_space == JCS_YCCK)
00447       cconvert->pub.color_convert = null_convert;
00448     else
00449       ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
00450     break;
00451 
00452   default:                  /* allow null conversion of JCS_UNKNOWN */
00453     if (cinfo->jpeg_color_space != cinfo->in_color_space ||
00454        cinfo->num_components != cinfo->input_components)
00455       ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
00456     cconvert->pub.color_convert = null_convert;
00457     break;
00458   }
00459 }