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* Copyright (C) 1991-1997, 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 output colorspace conversion routines.
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#define JPEG_INTERNALS
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/* Private subobject */
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struct jpeg_color_deconverter pub; /* public fields */
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/* Private state for YCC->RGB conversion */
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int * Cr_r_tab; /* => table for Cr to R conversion */
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int * Cb_b_tab; /* => table for Cb to B conversion */
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INT32 * Cr_g_tab; /* => table for Cr to G conversion */
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INT32 * Cb_g_tab; /* => table for Cb to G conversion */
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} my_color_deconverter;
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typedef my_color_deconverter * my_cconvert_ptr;
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/**************** YCbCr -> RGB 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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* R = Y + 1.40200 * Cr
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* G = Y - 0.34414 * Cb - 0.71414 * Cr
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* B = Y + 1.77200 * Cb
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* where Cb and Cr represent the incoming values less CENTERJSAMPLE.
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* (These numbers are derived from TIFF 6.0 section 21, dated 3-June-92.)
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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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* Notice that Y, being an integral input, does not contribute any fraction
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* so it need not participate in the rounding.
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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 Cb and Cr 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 Cr=>R and Cb=>B values can be rounded to integers in advance; the
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* values for the G calculation are left scaled up, since we must add them
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* together before rounding.
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#define SCALEBITS 16 /* speediest right-shift on some machines */
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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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* Initialize tables for YCC->RGB colorspace conversion.
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build_ycc_rgb_table (j_decompress_ptr cinfo)
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my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
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cconvert->Cr_r_tab = (int *)
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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(MAXJSAMPLE+1) * SIZEOF(int));
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cconvert->Cb_b_tab = (int *)
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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(MAXJSAMPLE+1) * SIZEOF(int));
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cconvert->Cr_g_tab = (INT32 *)
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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(MAXJSAMPLE+1) * SIZEOF(INT32));
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cconvert->Cb_g_tab = (INT32 *)
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(*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
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(MAXJSAMPLE+1) * SIZEOF(INT32));
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for (i = 0, x = -CENTERJSAMPLE; i <= MAXJSAMPLE; i++, x++) {
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/* i is the actual input pixel value, in the range 0..MAXJSAMPLE */
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/* The Cb or Cr value we are thinking of is x = i - CENTERJSAMPLE */
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/* Cr=>R value is nearest int to 1.40200 * x */
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cconvert->Cr_r_tab[i] = (int)
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RIGHT_SHIFT(FIX(1.40200) * x + ONE_HALF, SCALEBITS);
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/* Cb=>B value is nearest int to 1.77200 * x */
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cconvert->Cb_b_tab[i] = (int)
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RIGHT_SHIFT(FIX(1.77200) * x + ONE_HALF, SCALEBITS);
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/* Cr=>G value is scaled-up -0.71414 * x */
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cconvert->Cr_g_tab[i] = (- FIX(0.71414)) * x;
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/* Cb=>G value is scaled-up -0.34414 * x */
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/* We also add in ONE_HALF so that need not do it in inner loop */
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cconvert->Cb_g_tab[i] = (- FIX(0.34414)) * x + ONE_HALF;
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* Convert some rows of samples to the output colorspace.
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* Note that we change from noninterleaved, one-plane-per-component format
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* to interleaved-pixel format. The output buffer is therefore three times
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* as wide as the input buffer.
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* A starting row offset is provided only for the input buffer. The caller
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* can easily adjust the passed output_buf value to accommodate any row
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* offset required on that side.
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ycc_rgb_convert (j_decompress_ptr cinfo,
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JSAMPIMAGE input_buf, JDIMENSION input_row,
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JSAMPARRAY output_buf, int num_rows)
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my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
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register int y, cb, cr;
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register JSAMPROW outptr;
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register JSAMPROW inptr0, inptr1, inptr2;
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register JDIMENSION col;
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JDIMENSION num_cols = cinfo->output_width;
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/* copy these pointers into registers if possible */
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register JSAMPLE * range_limit = cinfo->sample_range_limit;
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register int * Crrtab = cconvert->Cr_r_tab;
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register int * Cbbtab = cconvert->Cb_b_tab;
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register INT32 * Crgtab = cconvert->Cr_g_tab;
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register INT32 * Cbgtab = cconvert->Cb_g_tab;
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while (--num_rows >= 0) {
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inptr0 = input_buf[0][input_row];
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inptr1 = input_buf[1][input_row];
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inptr2 = input_buf[2][input_row];
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outptr = *output_buf++;
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for (col = 0; col < num_cols; col++) {
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y = GETJSAMPLE(inptr0[col]);
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cb = GETJSAMPLE(inptr1[col]);
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cr = GETJSAMPLE(inptr2[col]);
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/* Range-limiting is essential due to noise introduced by DCT losses. */
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outptr[RGB_RED] = range_limit[y + Crrtab[cr]];
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outptr[RGB_GREEN] = range_limit[y +
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((int) RIGHT_SHIFT(Cbgtab[cb] + Crgtab[cr],
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outptr[RGB_BLUE] = range_limit[y + Cbbtab[cb]];
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outptr += RGB_PIXELSIZE;
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/**************** Cases other than YCbCr -> RGB **************/
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* Color conversion for no colorspace change: just copy the data,
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* converting from separate-planes to interleaved representation.
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null_convert (j_decompress_ptr cinfo,
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JSAMPIMAGE input_buf, JDIMENSION input_row,
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JSAMPARRAY output_buf, int num_rows)
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register JSAMPROW inptr, outptr;
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register JDIMENSION count;
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register int num_components = cinfo->num_components;
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JDIMENSION num_cols = cinfo->output_width;
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while (--num_rows >= 0) {
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for (ci = 0; ci < num_components; ci++) {
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inptr = input_buf[ci][input_row];
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outptr = output_buf[0] + ci;
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for (count = num_cols; count > 0; count--) {
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*outptr = *inptr++; /* needn't bother with GETJSAMPLE() here */
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outptr += num_components;
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* Color conversion for grayscale: just copy the data.
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* This also works for YCbCr -> grayscale conversion, in which
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* we just copy the Y (luminance) component and ignore chrominance.
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grayscale_convert (j_decompress_ptr cinfo,
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JSAMPIMAGE input_buf, JDIMENSION input_row,
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JSAMPARRAY output_buf, int num_rows)
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jcopy_sample_rows(input_buf[0], (int) input_row, output_buf, 0,
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num_rows, cinfo->output_width);
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* Convert grayscale to RGB: just duplicate the graylevel three times.
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* This is provided to support applications that don't want to cope
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* with grayscale as a separate case.
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gray_rgb_convert (j_decompress_ptr cinfo,
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JSAMPIMAGE input_buf, JDIMENSION input_row,
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JSAMPARRAY output_buf, int num_rows)
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register JSAMPROW inptr, outptr;
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register JDIMENSION col;
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JDIMENSION num_cols = cinfo->output_width;
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while (--num_rows >= 0) {
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inptr = input_buf[0][input_row++];
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outptr = *output_buf++;
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for (col = 0; col < num_cols; col++) {
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/* We can dispense with GETJSAMPLE() here */
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outptr[RGB_RED] = outptr[RGB_GREEN] = outptr[RGB_BLUE] = inptr[col];
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outptr += RGB_PIXELSIZE;
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* Adobe-style YCCK->CMYK conversion.
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* We convert YCbCr to R=1-C, G=1-M, and B=1-Y using the same
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* conversion as above, while passing K (black) unchanged.
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* We assume build_ycc_rgb_table has been called.
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ycck_cmyk_convert (j_decompress_ptr cinfo,
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JSAMPIMAGE input_buf, JDIMENSION input_row,
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JSAMPARRAY output_buf, int num_rows)
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my_cconvert_ptr cconvert = (my_cconvert_ptr) cinfo->cconvert;
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register int y, cb, cr;
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register JSAMPROW outptr;
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register JSAMPROW inptr0, inptr1, inptr2, inptr3;
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register JDIMENSION col;
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JDIMENSION num_cols = cinfo->output_width;
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/* copy these pointers into registers if possible */
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register JSAMPLE * range_limit = cinfo->sample_range_limit;
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register int * Crrtab = cconvert->Cr_r_tab;
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register int * Cbbtab = cconvert->Cb_b_tab;
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register INT32 * Crgtab = cconvert->Cr_g_tab;
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register INT32 * Cbgtab = cconvert->Cb_g_tab;
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while (--num_rows >= 0) {
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inptr0 = input_buf[0][input_row];
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inptr1 = input_buf[1][input_row];
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inptr2 = input_buf[2][input_row];
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inptr3 = input_buf[3][input_row];
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outptr = *output_buf++;
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for (col = 0; col < num_cols; col++) {
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y = GETJSAMPLE(inptr0[col]);
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cb = GETJSAMPLE(inptr1[col]);
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cr = GETJSAMPLE(inptr2[col]);
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/* Range-limiting is essential due to noise introduced by DCT losses. */
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outptr[0] = range_limit[MAXJSAMPLE - (y + Crrtab[cr])]; /* red */
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outptr[1] = range_limit[MAXJSAMPLE - (y + /* green */
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((int) RIGHT_SHIFT(Cbgtab[cb] + Crgtab[cr],
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outptr[2] = range_limit[MAXJSAMPLE - (y + Cbbtab[cb])]; /* blue */
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/* K passes through unchanged */
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outptr[3] = inptr3[col]; /* don't need GETJSAMPLE here */
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* Empty method for start_pass.
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start_pass_dcolor (j_decompress_ptr cinfo)
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* Module initialization routine for output colorspace conversion.
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jinit_color_deconverter (j_decompress_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_deconverter));
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cinfo->cconvert = (struct jpeg_color_deconverter *) cconvert;
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cconvert->pub.start_pass = start_pass_dcolor;
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/* Make sure num_components agrees with jpeg_color_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->num_components != 3)
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ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
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if (cinfo->num_components != 4)
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ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
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default: /* JCS_UNKNOWN can be anything */
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if (cinfo->num_components < 1)
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ERREXIT(cinfo, JERR_BAD_J_COLORSPACE);
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/* Set out_color_components and conversion method based on requested space.
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* Also clear the component_needed flags for any unused components,
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* so that earlier pipeline stages can avoid useless computation.
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switch (cinfo->out_color_space) {
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cinfo->out_color_components = 1;
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if (cinfo->jpeg_color_space == JCS_GRAYSCALE ||
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cinfo->jpeg_color_space == JCS_YCbCr) {
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cconvert->pub.color_convert = grayscale_convert;
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/* For color->grayscale conversion, only the Y (0) component is needed */
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for (ci = 1; ci < cinfo->num_components; ci++)
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cinfo->comp_info[ci].component_needed = FALSE;
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ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
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cinfo->out_color_components = RGB_PIXELSIZE;
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if (cinfo->jpeg_color_space == JCS_YCbCr) {
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cconvert->pub.color_convert = ycc_rgb_convert;
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build_ycc_rgb_table(cinfo);
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} else if (cinfo->jpeg_color_space == JCS_GRAYSCALE) {
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cconvert->pub.color_convert = gray_rgb_convert;
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} else if (cinfo->jpeg_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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cinfo->out_color_components = 4;
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if (cinfo->jpeg_color_space == JCS_YCCK) {
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cconvert->pub.color_convert = ycck_cmyk_convert;
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build_ycc_rgb_table(cinfo);
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} else if (cinfo->jpeg_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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/* Permit null conversion to same output space */
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if (cinfo->out_color_space == cinfo->jpeg_color_space) {
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cinfo->out_color_components = cinfo->num_components;
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cconvert->pub.color_convert = null_convert;
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} else /* unsupported non-null conversion */
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ERREXIT(cinfo, JERR_CONVERSION_NOTIMPL);
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if (cinfo->quantize_colors)
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cinfo->output_components = 1; /* single colormapped output component */
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cinfo->output_components = cinfo->out_color_components;
added
removed
JPEG/jpeg/jdcolor.c
