SXWRR@ALASKA.BITNET (Reed Rector) (05/13/89)
[GIF Image Decompression]
As promised weeks ago, here is some 'C' source code that will read and
decompress a GIF image file. (This program converts it to a Sun Raster
image, but it is no great problem converting for use in other programs)
Any problems or questions, just let me know
-Reed
SXWRR@ALASKA (Bitnet)
SXWRR@acad3.fai.alaska.edu (internet)
---
#! /bin/sh
# This is a shell archive, meaning:
# 1. Remove everything above the #! /bin/sh line.
# 2. Save the resulting text in a file.
# 3. Execute the file with /bin/sh (not csh) to create the files:
#
# gif2ras.c
#
# This archive created: Fri May 12 20:22:24 1989
# By: Roger L. Long (bytebug@dhw68k.cts.com)
export PATH; PATH=/bin:$PATH
echo shar: extracting "'gif2ras.c'" '(14611 characters)'
if test -f 'gif2ras.c'
then
echo shar: will not over-write existing file "'gif2ras.c'"
else
sed 's/^X//' << \SHAR_EOF > 'gif2ras.c'
X/*
X * gif2ras.c - Converts from a Compuserve GIF (tm) image to a Sun Raster image.
X *
X * Copyright (c) 1988 by Patrick J. Naughton
X *
X * Author: Patrick J. Naughton
X * naughton@wind.sun.com
X *
X * Permission to use, copy, modify, and distribute this software and its
X * documentation for any purpose and without fee is hereby granted,
X * provided that the above copyright notice appear in all copies and that
X * both that copyright notice and this permission notice appear in
X * supporting documentation.
X *
X * This file is provided AS IS with no warranties of any kind. The author
X * shall have no liability with respect to the infringement of copyrights,
X * trade secrets or any patents by this file or any part thereof. In no
X * event will the author be liable for any lost revenue or profits or
X * other special, indirect and consequential damages.
X *
X * Comments and additions should be sent to the author:
X *
X * Patrick J. Naughton
X * Sun Microsystems, Inc.
X * 2550 Garcia Ave, MS 14-40
X * Mountain View, CA 94043
X * (415) 336-1080
X *
X * Revision History:
X * 28-Aug-88: Modified by Jef Poskanzer to output PBM instead of Sun raster.
X * 27-Jul-88: Updated to use libpixrect to fix 386i byteswapping problems.
X * 11-Apr-88: Converted to C and changed to write Sun rasterfiles.
X * 19-Jan-88: GIFSLOW.PAS posted to comp.graphics by Jim Briebel,
X * a Turbo Pascal 4.0 program to painfully slowly display
X * GIF images on an EGA equipped IBM-PC.
X *
X * Description:
X * This program takes a Compuserve "Graphics Interchange Format" or "GIF"
X * file as input and writes a file known as a Sun rasterfile. This datafile
X * can be loaded by the NeWS "readcanvas" operator and is of the same format
X * as the files in /usr/NeWS/smi/*. Under X11R2 there is a program called
X * xraster to display these files.
X *
X * Portability:
X * To make this program convert to some image format other than PBM
X * format simply seach for the tag "PBMS:" in the source and
X * replace these simple mechanisms with the appropriate ones for the
X * other output format. I have marked all (six) PBM Specific pieces
X * of code with this comment.
X *
X * SS: compile with "cc -o gif2ras -O gif2ras.c -lpixrect"
X * PBMS: compile with "cc -o giftopbm -O giftopbm.c libpbm.a
X */
X
X#include <stdio.h>
X#ifdef notdefSS
X#include <pixrect/pixrect_hs.h> /* SS: main Pixrect header file */
X#endif notdefSS
X#include <sys/types.h>
X#include "pbm.h" /* PBMS: main PBM header file */
X
Xtypedef int boolean;
X#define True (1)
X#define False (0)
X
X#define NEXTSHORT (*ptr++ + (0x100 * *ptr++))
X#define NEXTBYTE (*ptr++)
X#define IMAGESEP 0x2c
X#define INTERLACEMASK 0x40
X#define COLORMAPMASK 0x80
X
Xint BitOffset = 0, /* Bit Offset of next code */
X XC = 0, YC = 0, /* Output X and Y coords of current pixel */
X Pass = 0, /* Used by output routine if interlaced pic */
X OutCount = 0, /* Decompressor output 'stack count' */
X RWidth, RHeight, /* screen dimensions */
X Width, Height, /* image dimensions */
X LeftOfs, TopOfs, /* image offset */
X BitsPerPixel, /* Bits per pixel, read from GIF header */
X ColorMapSize, /* number of colors */
X CodeSize, /* Code size, read from GIF header */
X InitCodeSize, /* Starting code size, used during Clear */
X Code, /* Value returned by ReadCode */
X MaxCode, /* limiting value for current code size */
X ClearCode, /* GIF clear code */
X EOFCode, /* GIF end-of-information code */
X CurCode, OldCode, InCode, /* Decompressor variables */
X FirstFree, /* First free code, generated per GIF spec */
X FreeCode, /* Decompressor, next free slot in hash table */
X FinChar, /* Decompressor variable */
X BitMask, /* AND mask for data size */
X ReadMask; /* Code AND mask for current code size */
X
Xboolean Interlace, HasColormap;
X
X#ifdef notdefSS
X/* SS: defined in pixrect/pixrect_hs.h */
XPixrect *Output; /* The Sun Pixrect */
Xcolormap_t Colormap; /* The Pixrect Colormap */
Xu_char *Image; /* The result array */
X#endif notdefSS
X/* PBMS: defined in pbm.h */
Xbit **bits; /* The PBM bit array */
X
Xu_char *RawGIF; /* The heap array to hold it, raw */
Xu_char *Raster; /* The raster data stream, unblocked */
X
X /* The hash table used by the decompressor */
Xint Prefix[4096];
Xint Suffix[4096];
X
X /* An output array used by the decompressor */
Xint OutCode[1025];
X
X /* The color map, read from the GIF header */
Xu_char Red[256], Green[256], Blue[256];
X
Xchar *id = "GIF87a";
X
Xchar *pname; /* program name (used for error messages) */
X
Xvoid
Xerror(s1, s2)
Xchar *s1, *s2;
X{
X fprintf(stderr, s1, pname, s2);
X exit(1);
X}
X
X
Xmain(argc, argv)
Xint argc;
Xchar *argv[];
X{
XFILE *fp;
Xchar *infname = argv[1];
Xchar *outfname = argv[2];
Xint filesize;
Xregister u_char ch, ch1;
Xregister u_char *ptr, *ptr1;
Xregister int i;
X
X setbuf(stderr, NULL);
X pname = argv[0];
X
X if (argc < 3)
X error("usage: %s GIFfile rasterfile\n", NULL);
X
X if (!(fp = fopen(infname, "r")))
X error("%s: %s not found.\n", infname);
X
X /* find the size of the file */
X
X fseek(fp, 0L, 2);
X filesize = ftell(fp);
X fseek(fp, 0L, 0);
X
X if (!(ptr = RawGIF = (u_char *) malloc(filesize)))
X error("%s: not enough memory to read gif file.\n", NULL);
X
X if (!(Raster = (u_char *) malloc(filesize)))
X error("%s: not enough memory to read gif file.\n", NULL);
X
X fread(ptr, filesize, 1, fp);
X
X if (strncmp(ptr, id, 6))
X error("%s: %s is not a GIF file.\n", infname);
X ptr += 6;
X
X/* Get variables from the GIF screen descriptor */
X
X RWidth = NEXTSHORT; /* screen dimensions... not used. */
X RHeight = NEXTSHORT;
X
X ch = NEXTBYTE;
X HasColormap = ((ch & COLORMAPMASK) ? True : False);
X
X BitsPerPixel = (ch & 7) + 1;
X ColorMapSize = 1 << BitsPerPixel;
X BitMask = ColorMapSize - 1;
X
X ch = NEXTBYTE; /* background color... not used. */
X
X if (NEXTBYTE) /* supposed to be NULL */
X error("%s: %s is a corrupt GIF file.\n", infname);
X
X/* Read in global colormap. */
X
X if (HasColormap) {
X fprintf(stderr, "%s is %d bits per pixel, (%d colors).\n",
X infname, BitsPerPixel, ColorMapSize);
X for (i = 0; i < ColorMapSize; i++) {
X Red[i] = NEXTBYTE;
X Green[i] = NEXTBYTE;
X Blue[i] = NEXTBYTE;
X }
X
X#ifdef notdefSS
X/* SS: Fill in the Pixrect colormap struct */
X Colormap.type = RMT_EQUAL_RGB;
X Colormap.length = ColorMapSize;
X Colormap.map[0] = Red;
X Colormap.map[1] = Green;
X Colormap.map[2] = Blue;
X#endif notdefSS
X /* PBMS: PBM only handles bitmaps. Reject any pixmaps here. */
X if (BitsPerPixel != 1)
X error("%s: %s has more than one bit per pixel - it's not a bitmap.\n
X", infname);
X }
X else error("%s: %s does not have a colormap.\n", infname);
X
X
X/* Check for image seperator */
X
X if (NEXTBYTE != IMAGESEP)
X error("%s: %s is a corrupt GIF file.\n", infname);
X
X/* Now read in values from the image descriptor */
X
X LeftOfs = NEXTSHORT;
X TopOfs = NEXTSHORT;
X Width = NEXTSHORT;
X Height = NEXTSHORT;
X Interlace = ((NEXTBYTE & INTERLACEMASK) ? True : False);
X
X fprintf(stderr, "Reading a %d by %d %sinterlaced image...",
X Width, Height, (Interlace) ? "" : "non-");
X
X
X/* Note that I ignore the possible existence of a local color map.
X * I'm told there aren't many files around that use them, and the spec
X * says it's defined for future use. This could lead to an error
X * reading some files.
X */
X
X/* Start reading the raster data. First we get the intial code size
X * and compute decompressor constant values, based on this code size.
X */
X
X CodeSize = NEXTBYTE;
X ClearCode = (1 << CodeSize);
X EOFCode = ClearCode + 1;
X FreeCode = FirstFree = ClearCode + 2;
X
X/* The GIF spec has it that the code size is the code size used to
X * compute the above values is the code size given in the file, but the
X * code size used in compression/decompression is the code size given in
X * the file plus one. (thus the ++).
X */
X
X CodeSize++;
X InitCodeSize = CodeSize;
X MaxCode = (1 << CodeSize);
X ReadMask = MaxCode - 1;
X
X/* Read the raster data. Here we just transpose it from the GIF array
X * to the Raster array, turning it from a series of blocks into one long
X * data stream, which makes life much easier for ReadCode().
X */
X
X ptr1 = Raster;
X do {
X ch = ch1 = NEXTBYTE;
X while (ch--) *ptr1++ = NEXTBYTE;
X } while(ch1);
X
X free(RawGIF); /* We're done with the raw data now... */
X
X fprintf(stderr, "done.\n");
X fprintf(stderr, "Decompressing...");
X
X
X#ifdef notdefSS
X/* SS: Allocate the Sun Pixrect and make "Image" point to the image data. */
X Output = mem_create(Width, Height, 8);
X if (Output == (Pixrect *) NULL)
X error("%s: not enough memory for output data.\n", NULL);
X Image = (u_char *) mpr_d(Output)->md_image;
X#endif notdefSS
X/* PBMS: Allocate the PBM bit array. */
X bits = pbm_allocarray(Width, Height);
X
X
X/* Decompress the file, continuing until you see the GIF EOF code.
X * One obvious enhancement is to add checking for corrupt files here.
X */
X
X Code = ReadCode();
X while (Code != EOFCode) {
X
X/* Clear code sets everything back to its initial value, then reads the
X * immediately subsequent code as uncompressed data.
X */
X
X if (Code == ClearCode) {
X CodeSize = InitCodeSize;
X MaxCode = (1 << CodeSize);
X ReadMask = MaxCode - 1;
X FreeCode = FirstFree;
X CurCode = OldCode = Code = ReadCode();
X FinChar = CurCode & BitMask;
X AddToPixel(FinChar);
X }
X else {
X
X/* If not a clear code, then must be data: save same as CurCode and InCode */
X
X CurCode = InCode = Code;
X
X/* If greater or equal to FreeCode, not in the hash table yet;
X * repeat the last character decoded
X */
X
X if (CurCode >= FreeCode) {
X CurCode = OldCode;
X OutCode[OutCount++] = FinChar;
X }
X
X/* Unless this code is raw data, pursue the chain pointed to by CurCode
X * through the hash table to its end; each code in the chain puts its
X * associated output code on the output queue.
X */
X
X while (CurCode > BitMask) {
X OutCode[OutCount++] = Suffix[CurCode];
X CurCode = Prefix[CurCode];
X }
X
X/* The last code in the chain is treated as raw data. */
X
X FinChar = CurCode & BitMask;
X OutCode[OutCount++] = FinChar;
X
X/* Now we put the data out to the Output routine.
X * It's been stacked LIFO, so deal with it that way...
X */
X
X for (i = OutCount - 1; i >= 0; i--)
X AddToPixel(OutCode[i]);
X OutCount = 0;
X
X/* Build the hash table on-the-fly. No table is stored in the file. */
X
X Prefix[FreeCode] = OldCode;
X Suffix[FreeCode] = FinChar;
X OldCode = InCode;
X
X/* Point to the next slot in the table. If we exceed the current
X * MaxCode value, increment the code size unless it's already 12. If it
X * is, do nothing: the next code decompressed better be CLEAR
X */
X
X FreeCode++;
X if (FreeCode >= MaxCode) {
X if (CodeSize < 12) {
X CodeSize++;
X MaxCode *= 2;
X ReadMask = (1 << CodeSize) - 1;
X }
X }
X }
X Code = ReadCode();
X }
X
X free(Raster);
X
X fprintf(stderr, "done.\n");
X
X if (!(fp = fopen(outfname, "w")))
X error("%s: can't create %s.\n", outfname);
X
X#ifdef notdefSS
X/* SS: Pixrect Rasterfile output code. */
X fprintf(stderr, "Writing Sun Rasterfile: %s...", outfname);
X if (pr_dump(Output, fp, &Colormap, RT_STANDARD, 0) == PIX_ERR)
X error("%s: error writing Sun Rasterfile: %s\n", outfname);
X#endif notdefSS
X/* PBMS: PBM output code. */
X pbm_writepbm(stdout, bits, Width, Height);
X
X fclose(fp);
X
X fprintf(stderr, "done.\n");
X}
X
X
X/* Fetch the next code from the raster data stream. The codes can be
X * any length from 3 to 12 bits, packed into 8-bit bytes, so we have to
X * maintain our location in the Raster array as a BIT Offset. We compute
X * the byte Offset into the raster array by dividing this by 8, pick up
X * three bytes, compute the bit Offset into our 24-bit chunk, shift to
X * bring the desired code to the bottom, then mask it off and return it.
X */
XReadCode()
X{
Xint RawCode, ByteOffset;
X
X ByteOffset = BitOffset / 8;
X RawCode = Raster[ByteOffset] + (0x100 * Raster[ByteOffset + 1]);
X if (CodeSize >= 8)
X RawCode += (0x10000 * Raster[ByteOffset + 2]);
X RawCode >>= (BitOffset % 8);
X BitOffset += CodeSize;
X return(RawCode & ReadMask);
X}
X
X
XAddToPixel(Index)
Xu_char Index;
X{
X#ifdef notdefSS
X *(Image + YC * Width + XC) = Index;
X#endif notdefSS
X/* PBMS: Store a pixel. */
X bits[YC][XC] = Index;
X
X/* Update the X-coordinate, and if it overflows, update the Y-coordinate */
X
X if (++XC == Width) {
X
X/* If a non-interlaced picture, just increment YC to the next scan line.
X * If it's interlaced, deal with the interlace as described in the GIF
X * spec. Put the decoded scan line out to the screen if we haven't gone
X * past the bottom of it
X */
X
X XC = 0;
X if (!Interlace) YC++;
X else {
X switch (Pass) {
X case 0:
X YC += 8;
X if (YC >= Height) {
X Pass++;
X YC = 4;
X }
X break;
X case 1:
X YC += 8;
X if (YC >= Height) {
X Pass++;
X YC = 2;
X }
X break;
X case 2:
X YC += 4;
X if (YC >= Height) {
X Pass++;
X YC = 1;
X }
X break;
X case 3:
X YC += 2;
X break;
X default:
X break;
X }
X }
X }
X}
SHAR_EOF
if test 14611 -ne "`wc -c < 'gif2ras.c'`"
then
echo shar: error transmitting "'gif2ras.c'" '(should have been 14611 characters)'
fi
fi # end of overwriting check
# End of shell archive
exit 0
---