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* Copyright (C) 1991-1996, Thomas G. Lane.
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* This file is part of the Independent JPEG Group's software.
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* For conditions of distribution and use, see the accompanying README file.
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* This file contains input colorspace conversion routines.
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#define JPEG_INTERNALS
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/* Private subobject */
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struct jpeg_color_converter pub; /* public fields */
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/* Private state for RGB->YCC conversion */
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INT32 * rgb_ycc_tab; /* => table for RGB to YCbCr conversion */
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typedef my_color_converter * my_cconvert_ptr;
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/**************** RGB -> YCbCr conversion: most common case **************/
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* YCbCr is defined per CCIR 601-1, except that Cb and Cr are
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* normalized to the range 0..MAXJSAMPLE rather than -0.5 .. 0.5.
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* The conversion equations to be implemented are therefore
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* Y = 0.29900 * R + 0.58700 * G + 0.11400 * B
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* Cb = -0.16874 * R - 0.33126 * G + 0.50000 * B + CENTERJSAMPLE
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* Cr = 0.50000 * R - 0.41869 * G - 0.08131 * B + CENTERJSAMPLE
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* (These numbers are derived from TIFF 6.0 section 21, dated 3-June-92.)
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* Note: older versions of the IJG code used a zero offset of MAXJSAMPLE/2,
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* rather than CENTERJSAMPLE, for Cb and Cr. This gave equal positive and
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* negative swings for Cb/Cr, but meant that grayscale values (Cb=Cr=0)
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* were not represented exactly. Now we sacrifice exact representation of
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* maximum red and maximum blue in order to get exact grayscales.
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* To avoid floating-point arithmetic, we represent the fractional constants
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* as integers scaled up by 2^16 (about 4 digits precision); we have to divide
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* the products by 2^16, with appropriate rounding, to get the correct answer.
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* For even more speed, we avoid doing any multiplications in the inner loop
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* by precalculating the constants times R,G,B for all possible values.
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* For 8-bit JSAMPLEs this is very reasonable (only 256 entries per table);
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* for 12-bit samples it is still acceptable. It's not very reasonable for
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* 16-bit samples, but if you want lossless storage you shouldn't be changing
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* The CENTERJSAMPLE offsets and the rounding fudge-factor of 0.5 are included
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* in the tables to save adding them separately in the inner loop.
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#define SCALEBITS 16 /* speediest right-shift on some machines */
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#define CBCR_OFFSET ((INT32) CENTERJSAMPLE << SCALEBITS)
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#define ONE_HALF ((INT32) 1 << (SCALEBITS-1))
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#define FIX(x) ((INT32) ((x) * (1L<<SCALEBITS) + 0.5))
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/* We allocate one big table and divide it up into eight parts, instead of
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* doing eight alloc_small requests. This lets us use a single table base
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* address, which can be held in a register in the inner loops on many
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* machines (more than can hold all eight addresses, anyway).
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#define R_Y_OFF 0 /* offset to R => Y section */
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#define G_Y_OFF (1*(MAXJSAMPLE+1)) /* offset to G => Y section */
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#define B_Y_OFF (2*(MAXJSAMPLE+1)) /* etc. */
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#define R_CB_OFF (3*(MAXJSAMPLE+1))
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#define G_CB_OFF (4*(MAXJSAMPLE+1))
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#define B_CB_OFF (5*(MAXJSAMPLE+1))
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#define R_CR_OFF B_CB_OFF /* B=>Cb, R=>Cr are the same */
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#define G_CR_OFF (6*(MAXJSAMPLE+1))
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#define B_CR_OFF (7*(MAXJSAMPLE+1))
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#define TABLE_SIZE (8*(MAXJSAMPLE+1))
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* Initialize for RGB->YCC colorspace conversion.
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rgb_ycc_start (j_compress_ptr cinfo)
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my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
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/* Allocate and fill in the conversion tables. */
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cconvert->rgb_ycc_tab = rgb_ycc_tab = (INT32 *)
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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(TABLE_SIZE * SIZEOF(INT32)));
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for (i = 0; i <= MAXJSAMPLE; i++) {
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rgb_ycc_tab[i+R_Y_OFF] = FIX(0.29900) * i;
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rgb_ycc_tab[i+G_Y_OFF] = FIX(0.58700) * i;
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rgb_ycc_tab[i+B_Y_OFF] = FIX(0.11400) * i + ONE_HALF;
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rgb_ycc_tab[i+R_CB_OFF] = (-FIX(0.16874)) * i;
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rgb_ycc_tab[i+G_CB_OFF] = (-FIX(0.33126)) * i;
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/* We use a rounding fudge-factor of 0.5-epsilon for Cb and Cr.
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* This ensures that the maximum output will round to MAXJSAMPLE
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* not MAXJSAMPLE+1, and thus that we don't have to range-limit.
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rgb_ycc_tab[i+B_CB_OFF] = FIX(0.50000) * i + CBCR_OFFSET + ONE_HALF-1;
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/* B=>Cb and R=>Cr tables are the same
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rgb_ycc_tab[i+R_CR_OFF] = FIX(0.50000) * i + CBCR_OFFSET + ONE_HALF-1;
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rgb_ycc_tab[i+G_CR_OFF] = (-FIX(0.41869)) * i;
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rgb_ycc_tab[i+B_CR_OFF] = (-FIX(0.08131)) * i;
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* Convert some rows of samples to the JPEG colorspace.
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* Note that we change from the application's interleaved-pixel format
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* to our internal noninterleaved, one-plane-per-component format.
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* The input buffer is therefore three times as wide as the output buffer.
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* A starting row offset is provided only for the output buffer. The caller
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* can easily adjust the passed input_buf value to accommodate any row
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* offset required on that side.
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rgb_ycc_convert (j_compress_ptr cinfo,
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JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
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JDIMENSION output_row, int num_rows)
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my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
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register int r, g, b;
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register INT32 * ctab = cconvert->rgb_ycc_tab;
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register JSAMPROW inptr;
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register JSAMPROW outptr0, outptr1, outptr2;
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register JDIMENSION col;
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JDIMENSION num_cols = cinfo->image_width;
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while (--num_rows >= 0) {
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inptr = *input_buf++;
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outptr0 = output_buf[0][output_row];
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outptr1 = output_buf[1][output_row];
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outptr2 = output_buf[2][output_row];
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for (col = 0; col < num_cols; col++) {
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r = GETJSAMPLE(inptr[RGB_RED]);
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g = GETJSAMPLE(inptr[RGB_GREEN]);
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b = GETJSAMPLE(inptr[RGB_BLUE]);
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inptr += RGB_PIXELSIZE;
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/* If the inputs are 0..MAXJSAMPLE, the outputs of these equations
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* must be too; we do not need an explicit range-limiting operation.
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* Hence the value being shifted is never negative, and we don't
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* need the general RIGHT_SHIFT macro.
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outptr0[col] = (JSAMPLE)
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((ctab[r+R_Y_OFF] + ctab[g+G_Y_OFF] + ctab[b+B_Y_OFF])
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outptr1[col] = (JSAMPLE)
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((ctab[r+R_CB_OFF] + ctab[g+G_CB_OFF] + ctab[b+B_CB_OFF])
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outptr2[col] = (JSAMPLE)
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((ctab[r+R_CR_OFF] + ctab[g+G_CR_OFF] + ctab[b+B_CR_OFF])
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/**************** Cases other than RGB -> YCbCr **************/
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* Convert some rows of samples to the JPEG colorspace.
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* This version handles RGB->grayscale conversion, which is the same
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* as the RGB->Y portion of RGB->YCbCr.
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* We assume rgb_ycc_start has been called (we only use the Y tables).
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rgb_gray_convert (j_compress_ptr cinfo,
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JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
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JDIMENSION output_row, int num_rows)
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my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
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register int r, g, b;
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register INT32 * ctab = cconvert->rgb_ycc_tab;
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register JSAMPROW inptr;
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register JSAMPROW outptr;
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register JDIMENSION col;
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JDIMENSION num_cols = cinfo->image_width;
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while (--num_rows >= 0) {
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inptr = *input_buf++;
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outptr = output_buf[0][output_row];
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for (col = 0; col < num_cols; col++) {
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r = GETJSAMPLE(inptr[RGB_RED]);
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g = GETJSAMPLE(inptr[RGB_GREEN]);
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b = GETJSAMPLE(inptr[RGB_BLUE]);
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inptr += RGB_PIXELSIZE;
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outptr[col] = (JSAMPLE)
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((ctab[r+R_Y_OFF] + ctab[g+G_Y_OFF] + ctab[b+B_Y_OFF])
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* Convert some rows of samples to the JPEG colorspace.
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* This version handles Adobe-style CMYK->YCCK conversion,
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* where we convert R=1-C, G=1-M, and B=1-Y to YCbCr using the same
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* conversion as above, while passing K (black) unchanged.
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* We assume rgb_ycc_start has been called.
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cmyk_ycck_convert (j_compress_ptr cinfo,
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JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
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JDIMENSION output_row, int num_rows)
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my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
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register int r, g, b;
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register INT32 * ctab = cconvert->rgb_ycc_tab;
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register JSAMPROW inptr;
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register JSAMPROW outptr0, outptr1, outptr2, outptr3;
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register JDIMENSION col;
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JDIMENSION num_cols = cinfo->image_width;
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while (--num_rows >= 0) {
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inptr = *input_buf++;
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outptr0 = output_buf[0][output_row];
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outptr1 = output_buf[1][output_row];
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outptr2 = output_buf[2][output_row];
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outptr3 = output_buf[3][output_row];
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for (col = 0; col < num_cols; col++) {
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r = MAXJSAMPLE - GETJSAMPLE(inptr[0]);
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g = MAXJSAMPLE - GETJSAMPLE(inptr[1]);
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b = MAXJSAMPLE - GETJSAMPLE(inptr[2]);
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/* K passes through as-is */
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outptr3[col] = inptr[3]; /* don't need GETJSAMPLE here */
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/* If the inputs are 0..MAXJSAMPLE, the outputs of these equations
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* must be too; we do not need an explicit range-limiting operation.
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* Hence the value being shifted is never negative, and we don't
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* need the general RIGHT_SHIFT macro.
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outptr0[col] = (JSAMPLE)
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((ctab[r+R_Y_OFF] + ctab[g+G_Y_OFF] + ctab[b+B_Y_OFF])
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outptr1[col] = (JSAMPLE)
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((ctab[r+R_CB_OFF] + ctab[g+G_CB_OFF] + ctab[b+B_CB_OFF])
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outptr2[col] = (JSAMPLE)
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((ctab[r+R_CR_OFF] + ctab[g+G_CR_OFF] + ctab[b+B_CR_OFF])
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* Convert some rows of samples to the JPEG colorspace.
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* This version handles grayscale output with no conversion.
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* The source can be either plain grayscale or YCbCr (since Y == gray).
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grayscale_convert (j_compress_ptr cinfo,
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JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
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JDIMENSION output_row, int num_rows)
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register JSAMPROW inptr;
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register JSAMPROW outptr;
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register JDIMENSION col;
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JDIMENSION num_cols = cinfo->image_width;
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int instride = cinfo->input_components;
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while (--num_rows >= 0) {
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inptr = *input_buf++;
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outptr = output_buf[0][output_row];
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for (col = 0; col < num_cols; col++) {
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outptr[col] = inptr[0]; /* don't need GETJSAMPLE() here */
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* Convert some rows of samples to the JPEG colorspace.
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* This version handles multi-component colorspaces without conversion.
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* We assume input_components == num_components.
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null_convert (j_compress_ptr cinfo,
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JSAMPARRAY input_buf, JSAMPIMAGE output_buf,
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JDIMENSION output_row, int num_rows)
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register JSAMPROW inptr;
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register JSAMPROW outptr;
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register JDIMENSION col;
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int nc = cinfo->num_components;
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JDIMENSION num_cols = cinfo->image_width;
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while (--num_rows >= 0) {
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/* It seems fastest to make a separate pass for each component. */
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for (ci = 0; ci < nc; ci++) {
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outptr = output_buf[ci][output_row];
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for (col = 0; col < num_cols; col++) {
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outptr[col] = inptr[ci]; /* don't need GETJSAMPLE() here */
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* Empty method for start_pass.
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null_method (j_compress_ptr cinfo)
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* Module initialization routine for input colorspace conversion.
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jinit_color_converter (j_compress_ptr cinfo)
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my_cconvert_ptr cconvert;
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cconvert = (my_cconvert_ptr)
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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SIZEOF(my_color_converter));
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cinfo->cconvert = (struct jpeg_color_converter *) cconvert;
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/* set start_pass to null method until we find out differently */
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cconvert->pub.start_pass = null_method;
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/* Make sure input_components agrees with in_color_space */
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switch (cinfo->in_color_space) {
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if (cinfo->input_components != 1)
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ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
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#if RGB_PIXELSIZE != 3
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if (cinfo->input_components != RGB_PIXELSIZE)
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ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
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#endif /* else share code with YCbCr */
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if (cinfo->input_components != 3)
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ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
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if (cinfo->input_components != 4)
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ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
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default: /* JCS_UNKNOWN can be anything */
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if (cinfo->input_components < 1)
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ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
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/* Check num_components, set conversion method based on requested space */
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switch (cinfo->jpeg_color_space) {
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if (cinfo->num_components != 1)
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ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
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if (cinfo->in_color_space == JCS_GRAYSCALE)
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cconvert->pub.color_convert = grayscale_convert;
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else if (cinfo->in_color_space == JCS_RGB) {
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cconvert->pub.start_pass = rgb_ycc_start;
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cconvert->pub.color_convert = rgb_gray_convert;
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} else if (cinfo->in_color_space == JCS_YCbCr)
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cconvert->pub.color_convert = grayscale_convert;
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ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
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if (cinfo->num_components != 3)
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ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
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if (cinfo->in_color_space == JCS_RGB && RGB_PIXELSIZE == 3)
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cconvert->pub.color_convert = null_convert;
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ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
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if (cinfo->num_components != 3)
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ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
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if (cinfo->in_color_space == JCS_RGB) {
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cconvert->pub.start_pass = rgb_ycc_start;
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cconvert->pub.color_convert = rgb_ycc_convert;
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} else if (cinfo->in_color_space == JCS_YCbCr)
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cconvert->pub.color_convert = null_convert;
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ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
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if (cinfo->num_components != 4)
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ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
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if (cinfo->in_color_space == JCS_CMYK)
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cconvert->pub.color_convert = null_convert;
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ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
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if (cinfo->num_components != 4)
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ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
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if (cinfo->in_color_space == JCS_CMYK) {
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cconvert->pub.start_pass = rgb_ycc_start;
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cconvert->pub.color_convert = cmyk_ycck_convert;
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} else if (cinfo->in_color_space == JCS_YCCK)
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cconvert->pub.color_convert = null_convert;
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ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
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default: /* allow null conversion of JCS_UNKNOWN */
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if (cinfo->jpeg_color_space != cinfo->in_color_space ||
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cinfo->num_components != cinfo->input_components)
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ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
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cconvert->pub.color_convert = null_convert;