/*
* jccolor.c
*
* Copyright (C) 1991-1996, 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"
// this enables unrolling null_convert's loop, and reading/write ints for speed
#define ENABLE_ANDROID_NULL_CONVERT
/* 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);
}
}
}
#ifdef ANDROID_RGB
/* Converts RGB565 row into YCbCr */
METHODDEF(void)
rgb565_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 unsigned short* inptr;
register JSAMPROW outptr0, outptr1, outptr2;
register JDIMENSION col;
JDIMENSION num_cols = cinfo->image_width;
while (--num_rows >= 0) {
inptr = (unsigned short*)(*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++) {
register const unsigned short color = inptr[col];
r = ((color & 0xf800) >> 8) | ((color & 0xf800) >> 14);
g = ((color & 0x7e0) >> 3) | ((color & 0x7e0) >> 9);
b = ((color & 0x1f) << 3) | ((color & 0x1f) >> 2);
/* 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);
}
}
}
/* Converts RGBA8888 row into YCbCr */
METHODDEF(void)
rgba8888_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 INT32* inptr;
register JSAMPROW outptr0, outptr1, outptr2;
register JDIMENSION col;
JDIMENSION num_cols = cinfo->image_width;
while (--num_rows >= 0) {
inptr = (INT32*)(*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++) {
register const unsigned char* color = (unsigned char*)(inptr + col);
r = (*color) & 0xff; color++;
g = (*color) & 0xff; color++;
b = (*color) & 0xff; color++;
/* 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);
}
}
}
#endif /* ANDROID_RGB */
/**************** 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;
}
}
}
#ifdef ENABLE_ANDROID_NULL_CONVERT
typedef unsigned long UINT32;
#define B0(n) ((n) & 0xFF)
#define B1(n) (((n) >> 8) & 0xFF)
#define B2(n) (((n) >> 16) & 0xFF)
#define B3(n) ((n) >> 24)
#define PACK(a, b, c, d) ((a) | ((b) << 8) | ((c) << 16) | ((d) << 24))
static int ptr_is_quad(const void* p)
{
return (((const char*)p - (const char*)0) & 3) == 0;
}
static void copyquads(const UINT32 in[], UINT32 out0[], UINT32 out1[], UINT32 out2[], int col4)
{
do {
UINT32 src0 = *in++;
UINT32 src1 = *in++;
UINT32 src2 = *in++;
// LEndian
*out0++ = PACK(B0(src0), B3(src0), B2(src1), B1(src2));
*out1++ = PACK(B1(src0), B0(src1), B3(src1), B2(src2));
*out2++ = PACK(B2(src0), B1(src1), B0(src2), B3(src2));
} while (--col4 != 0);
}
#endif
/*
* 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;
#ifdef ENABLE_ANDROID_NULL_CONVERT
if (1 == num_rows && 3 == nc && num_cols > 0) {
JSAMPROW inptr = *input_buf;
JSAMPROW outptr0 = output_buf[0][output_row];
JSAMPROW outptr1 = output_buf[1][output_row];
JSAMPROW outptr2 = output_buf[2][output_row];
int col = num_cols;
int col4 = col >> 2;
if (col4 > 0 && ptr_is_quad(inptr) && ptr_is_quad(outptr0) &&
ptr_is_quad(outptr1) && ptr_is_quad(outptr2)) {
const UINT32* in = (const UINT32*)inptr;
UINT32* out0 = (UINT32*)outptr0;
UINT32* out1 = (UINT32*)outptr1;
UINT32* out2 = (UINT32*)outptr2;
copyquads(in, out0, out1, out2, col4);
col &= 3;
if (0 == col)
return;
col4 <<= 2;
inptr += col4 * 3; /* we read this 3 times per in copyquads */
outptr0 += col4;
outptr1 += col4;
outptr2 += col4;
/* fall through to while-loop */
}
do {
*outptr0++ = *inptr++;
*outptr1++ = *inptr++;
*outptr2++ = *inptr++;
} while (--col != 0);
return;
}
SLOW:
#endif
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;
#ifdef ANDROID_RGB
case JCS_RGB_565:
if (cinfo->input_components != 2)
ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
break;
case JCS_RGBA_8888:
if (cinfo->input_components != 4)
ERREXIT(cinfo, JERR_BAD_IN_COLORSPACE);
break;
#endif /* ANDROID_RGB */
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;
}
#ifdef ANDROID_RGB
else if (cinfo->in_color_space == JCS_RGB_565) {
cconvert->pub.start_pass = rgb_ycc_start;
cconvert->pub.color_convert = rgb565_ycc_convert;
} else if (cinfo->in_color_space == JCS_RGBA_8888) {
cconvert->pub.start_pass = rgb_ycc_start;
cconvert->pub.color_convert = rgba8888_ycc_convert;
}
#endif /* ANDROID_RGB */
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;
}
}