/* * jccolor.c * * Copyright (C) 1991, 1992, 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. * These routines are invoked via the methods get_sample_rows * and colorin_init/term. */ #include "jinclude.h" static JSAMPARRAY pixel_row; /* Workspace for a pixel row in input format */ /* * Initialize for colorspace conversion. */ METHODDEF void colorin_init (compress_info_ptr cinfo) { /* Allocate a workspace for the result of get_input_row. */ pixel_row = (*cinfo->emethods->alloc_small_sarray) (cinfo->image_width, (long) cinfo->input_components); } /* * Fetch some rows of pixels from get_input_row and convert to the * JPEG colorspace. */ /* * This version handles RGB -> YCbCr conversion. * 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 * Cr = 0.50000 * R - 0.41869 * G - 0.08131 * B * where Cb and Cr must be incremented by MAXJSAMPLE/2 to create a * nonnegative output value. * (These numbers are derived from TIFF Appendix O, draft of 4/10/91.) * * To avoid floating-point arithmetic, we represent the fractional constants * as integers scaled up by 2^14 (about 4 digits precision); we have to divide * the products by 2^14, with appropriate rounding, to get the correct answer. * * For even more speed, we could avoid any multiplications in the inner loop * by precalculating the constants times R,G,B for all possible values. * This is not currently implemented. */ #define SCALEBITS 14 #define ONE_HALF ((INT32) 1 << (SCALEBITS-1)) #define FIX(x) ((INT32) ((x) * (1L<image_width; int row; for (row = 0; row < rows_to_read; row++) { /* Read one row from the source file */ (*cinfo->methods->get_input_row) (cinfo, pixel_row); /* Convert colorspace */ inptr0 = pixel_row[0]; inptr1 = pixel_row[1]; inptr2 = pixel_row[2]; outptr0 = image_data[0][row]; outptr1 = image_data[1][row]; outptr2 = image_data[2][row]; for (col = width; col > 0; col--) { r = GETJSAMPLE(*inptr0++); g = GETJSAMPLE(*inptr1++); b = GETJSAMPLE(*inptr2++); /* 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++ = (JSAMPLE) (( FIX(0.29900)*r + FIX(0.58700)*g + FIX(0.11400)*b + ONE_HALF) >> SCALEBITS); /* Cb */ *outptr1++ = (JSAMPLE) (((-FIX(0.16874))*r - FIX(0.33126)*g + FIX(0.50000)*b + ONE_HALF*(MAXJSAMPLE+1)) >> SCALEBITS); /* Cr */ *outptr2++ = (JSAMPLE) (( FIX(0.50000)*r - FIX(0.41869)*g - FIX(0.08131)*b + ONE_HALF*(MAXJSAMPLE+1)) >> SCALEBITS); } } } /* * Fetch some rows of pixels from get_input_row and convert to the * JPEG colorspace. * This version handles grayscale (no conversion). */ METHODDEF void get_grayscale_rows (compress_info_ptr cinfo, int rows_to_read, JSAMPIMAGE image_data) { int row; for (row = 0; row < rows_to_read; row++) { /* Read one row from the source file */ (*cinfo->methods->get_input_row) (cinfo, pixel_row); /* Convert colorspace (gamma mapping needed here) */ jcopy_sample_rows(pixel_row, 0, image_data[0], row, 1, cinfo->image_width); } } /* * Fetch some rows of pixels from get_input_row and convert to the * JPEG colorspace. * This version handles multi-component colorspaces without conversion. */ METHODDEF void get_noconvert_rows (compress_info_ptr cinfo, int rows_to_read, JSAMPIMAGE image_data) { int row, ci; for (row = 0; row < rows_to_read; row++) { /* Read one row from the source file */ (*cinfo->methods->get_input_row) (cinfo, pixel_row); /* Convert colorspace (gamma mapping needed here) */ for (ci = 0; ci < cinfo->input_components; ci++) { jcopy_sample_rows(pixel_row, ci, image_data[ci], row, 1, cinfo->image_width); } } } /* * Finish up at the end of the file. */ METHODDEF void colorin_term (compress_info_ptr cinfo) { /* no work (we let free_all release the workspace) */ } /* * The method selection routine for input colorspace conversion. */ GLOBAL void jselccolor (compress_info_ptr cinfo) { /* Make sure input_components agrees with in_color_space */ switch (cinfo->in_color_space) { case CS_GRAYSCALE: if (cinfo->input_components != 1) ERREXIT(cinfo->emethods, "Bogus input colorspace"); break; case CS_RGB: case CS_YCbCr: case CS_YIQ: if (cinfo->input_components != 3) ERREXIT(cinfo->emethods, "Bogus input colorspace"); break; case CS_CMYK: if (cinfo->input_components != 4) ERREXIT(cinfo->emethods, "Bogus input colorspace"); break; default: ERREXIT(cinfo->emethods, "Unsupported input colorspace"); break; } /* Check num_components, set conversion method based on requested space */ switch (cinfo->jpeg_color_space) { case CS_GRAYSCALE: if (cinfo->num_components != 1) ERREXIT(cinfo->emethods, "Bogus JPEG colorspace"); if (cinfo->in_color_space == CS_GRAYSCALE) cinfo->methods->get_sample_rows = get_grayscale_rows; else ERREXIT(cinfo->emethods, "Unsupported color conversion request"); break; case CS_YCbCr: if (cinfo->num_components != 3) ERREXIT(cinfo->emethods, "Bogus JPEG colorspace"); if (cinfo->in_color_space == CS_RGB) cinfo->methods->get_sample_rows = get_rgb_ycc_rows; else if (cinfo->in_color_space == CS_YCbCr) cinfo->methods->get_sample_rows = get_noconvert_rows; else ERREXIT(cinfo->emethods, "Unsupported color conversion request"); break; case CS_CMYK: if (cinfo->num_components != 4) ERREXIT(cinfo->emethods, "Bogus JPEG colorspace"); if (cinfo->in_color_space == CS_CMYK) cinfo->methods->get_sample_rows = get_noconvert_rows; else ERREXIT(cinfo->emethods, "Unsupported color conversion request"); break; default: ERREXIT(cinfo->emethods, "Unsupported JPEG colorspace"); break; } cinfo->methods->colorin_init = colorin_init; cinfo->methods->colorin_term = colorin_term; }