tif_thunder.c

一个国人自己实现图像库的程序（有参考价值）

/* $Header: /cvsroot/osrs/libtiff/libtiff/tif_thunder.c,v 1.1.1.1 1999/07/27 21:50:27 mike Exp $ */

/*
 * Copyright (c) 1988-1997 Sam Leffler
 * Copyright (c) 1991-1997 Silicon Graphics, Inc.
 *
 * Permission to use, copy, modify, distribute, and sell this software and 
 * its documentation for any purpose is hereby granted without fee, provided
 * that (i) the above copyright notices and this permission notice appear in
 * all copies of the software and related documentation, and (ii) the names of
 * Sam Leffler and Silicon Graphics may not be used in any advertising or
 * publicity relating to the software without the specific, prior written
 * permission of Sam Leffler and Silicon Graphics.
 * 
 * THE SOFTWARE IS PROVIDED "AS-IS" AND WITHOUT WARRANTY OF ANY KIND, 
 * EXPRESS, IMPLIED OR OTHERWISE, INCLUDING WITHOUT LIMITATION, ANY 
 * WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.  
 * 
 * IN NO EVENT SHALL SAM LEFFLER OR SILICON GRAPHICS BE LIABLE FOR
 * ANY SPECIAL, INCIDENTAL, INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY KIND,
 * OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
 * WHETHER OR NOT ADVISED OF THE POSSIBILITY OF DAMAGE, AND ON ANY THEORY OF 
 * LIABILITY, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE 
 * OF THIS SOFTWARE.
 */

#include "tiffiop.h"
#ifdef THUNDER_SUPPORT
/*
 * TIFF Library.
 *
 * ThunderScan 4-bit Compression Algorithm Support
 */

/*
 * ThunderScan uses an encoding scheme designed for
 * 4-bit pixel values.  Data is encoded in bytes, with
 * each byte split into a 2-bit code word and a 6-bit
 * data value.  The encoding gives raw data, runs of
 * pixels, or pixel values encoded as a delta from the
 * previous pixel value.  For the latter, either 2-bit
 * or 3-bit delta values are used, with the deltas packed
 * into a single byte.
 */
#define	THUNDER_DATA		0x3f	/* mask for 6-bit data */
#define	THUNDER_CODE		0xc0	/* mask for 2-bit code word */
/* code values */
#define	THUNDER_RUN		0x00	/* run of pixels w/ encoded count */
#define	THUNDER_2BITDELTAS	0x40	/* 3 pixels w/ encoded 2-bit deltas */
#define	    DELTA2_SKIP		2	/* skip code for 2-bit deltas */
#define	THUNDER_3BITDELTAS	0x80	/* 2 pixels w/ encoded 3-bit deltas */
#define	    DELTA3_SKIP		4	/* skip code for 3-bit deltas */
#define	THUNDER_RAW		0xc0	/* raw data encoded */

static const int twobitdeltas[4] = { 0, 1, 0, -1 };
static const int threebitdeltas[8] = { 0, 1, 2, 3, 0, -3, -2, -1 };

#define	SETPIXEL(op, v) { \
	lastpixel = (v) & 0xf; \
	if (npixels++ & 1) \
	    *op++ |= lastpixel; \
	else \
	    op[0] = lastpixel << 4; \
}

static int
ThunderDecode(TIFF* tif, tidata_t op, tsize_t maxpixels)
{
	register u_char *bp;
	register tsize_t cc;
	u_int lastpixel;
	tsize_t npixels;

	bp = (u_char *)tif->tif_rawcp;
	cc = tif->tif_rawcc;
	lastpixel = 0;
	npixels = 0;
	while (cc > 0 && npixels < maxpixels) {
		int n, delta;

		n = *bp++, cc--;
		switch (n & THUNDER_CODE) {
		case THUNDER_RUN:		/* pixel run */
			/*
			 * Replicate the last pixel n times,
			 * where n is the lower-order 6 bits.
			 */
			if (npixels & 1) {
				op[0] |= lastpixel;
				lastpixel = *op++; npixels++; n--;
			} else
				lastpixel |= lastpixel << 4;
			npixels += n;
			for (; n > 0; n -= 2)
				*op++ = lastpixel;
			if (n == -1)
				*--op &= 0xf0;
			lastpixel &= 0xf;
			break;
		case THUNDER_2BITDELTAS:	/* 2-bit deltas */
			if ((delta = ((n >> 4) & 3)) != DELTA2_SKIP)
				SETPIXEL(op, lastpixel + twobitdeltas[delta]);
			if ((delta = ((n >> 2) & 3)) != DELTA2_SKIP)
				SETPIXEL(op, lastpixel + twobitdeltas[delta]);
			if ((delta = (n & 3)) != DELTA2_SKIP)
				SETPIXEL(op, lastpixel + twobitdeltas[delta]);
			break;
		case THUNDER_3BITDELTAS:	/* 3-bit deltas */
			if ((delta = ((n >> 3) & 7)) != DELTA3_SKIP)
				SETPIXEL(op, lastpixel + threebitdeltas[delta]);
			if ((delta = (n & 7)) != DELTA3_SKIP)
				SETPIXEL(op, lastpixel + threebitdeltas[delta]);
			break;
		case THUNDER_RAW:		/* raw data */
			SETPIXEL(op, n);
			break;
		}
	}
	tif->tif_rawcp = (tidata_t) bp;
	tif->tif_rawcc = cc;
	if (npixels != maxpixels) {
		TIFFError(tif->tif_name,
		    "ThunderDecode: %s data at scanline %ld (%lu != %lu)",
		    npixels < maxpixels ? "Not enough" : "Too much",
		    (long) tif->tif_row, (long) npixels, (long) maxpixels);
		return (0);
	}
	return (1);
}

static int
ThunderDecodeRow(TIFF* tif, tidata_t buf, tsize_t occ, tsample_t s)
{
	tidata_t row = buf;
	
	(void) s;
	while ((long)occ > 0) {
		if (!ThunderDecode(tif, row, tif->tif_dir.td_imagewidth))
			return (0);
		occ -= tif->tif_scanlinesize;
		row += tif->tif_scanlinesize;
	}
	return (1);
}

int
TIFFInitThunderScan(TIFF* tif, int scheme)
{
	(void) scheme;
	tif->tif_decoderow = ThunderDecodeRow;
	tif->tif_decodestrip = ThunderDecodeRow;
	return (1);
}
#endif /* THUNDER_SUPPORT */