jccolor.c

/*
 * jccolor.c
 *
 * Copyright (C) 1991-1994, 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.
 */

#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.
 * 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 RGB_PIXELSIZE != 3
		if ( cinfo->input_components != RGB_PIXELSIZE ) {
			ERREXIT( cinfo, JERR_BAD_IN_COLORSPACE );
		}
		break;
#endif /* else share code with YCbCr */

	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 ) {
			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 if ( cinfo->in_color_space == JCS_YCbCr ) {
			cconvert->pub.color_convert = grayscale_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 && RGB_PIXELSIZE == 3 ) {
			cconvert->pub.color_convert = null_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;
	}
}