mgardi@watdcsu.waterloo.edu (M.Gardi - ICR) (02/10/89)
Here is some source for GIF image compression. It is set up for MSDOS, but is trivial to modify for non-DOS machines (change the open for write to "w" instead of "wb", remove the define for MSDOS, etc). The source started out as the lempel-ziv 'compress' routine, and was modified to output GIF files. To use the GIFEncode function, define a function 'GetPixel' that takes an X and Y co-ordinate (as int's) and returns the colour index of that pixel. Then call GIFEncode with the following: GIFEncode( Fname, /* The filename to write */ GHeight, /* The height of the bitmap - an int */ GWidth, /* The width of the bitmap - an int */ GInterlace, /* TRUE if you want the image to be interlaced, FALSE otherwise */ Background, /* The colour index of the background */ BitsPerPixel, /* The number of bits of color per pixel in the palette you specified. If your palette has 256 colours, it should be '8', 32 should be '5', etc */ Red, Green, Blue, /* Pointers to arrays of int's, containing the R, G and B values of the colour palette */ GetPixel ); /* a pointer to a function that returns the index of the colour at the co-ordinates passed */ ----------cut here------------------cut here-------------------------------- #!/bin/sh # This is a shell archive. Remove anything before this line, # then unpack it by saving it in a file and typing "sh file". # # Wrapped by watdcsu!mgardi on Thu Feb 9 18:19:39 EST 1989 # Contents: gifcompr.c gifencod.c echo x - gifcompr.c sed 's/^@//' > "gifcompr.c" <<'@//E*O*F gifcompr.c//' /*************************************************************************** * * GIFENCOD.C - GIF Image compression routines * * Lempel-Ziv compression based on 'compress'. GIF modifications by * David Rowley (mgardi@watdcsu.waterloo.edu) * ***************************************************************************/ /* * General DEFINEs */ #define min(a,b) ((a>b) ? b : a) #define BITS 12 #define MSDOS 1 #define HSIZE 5003 /* 80% occupancy */ /* * Pointer to function returning an int */ typedef int (* ifunptr)(); /* * a code_int must be able to hold 2**BITS values of type int, and also -1 */ typedef int code_int; #ifdef SIGNED_COMPARE_SLOW typedef unsigned long int count_int; typedef unsigned short int count_short; #else typedef long int count_int; #endif #ifdef NO_UCHAR typedef char char_type; #else typedef unsigned char char_type; #endif /* UCHAR */ /* * * GIF Image compression - modified 'compress' * * Based on: compress.c - File compression ala IEEE Computer, June 1984. * * By Authors: Spencer W. Thomas (decvax!harpo!utah-cs!utah-gr!thomas) * Jim McKie (decvax!mcvax!jim) * Steve Davies (decvax!vax135!petsd!peora!srd) * Ken Turkowski (decvax!decwrl!turtlevax!ken) * James A. Woods (decvax!ihnp4!ames!jaw) * Joe Orost (decvax!vax135!petsd!joe) * */ #include <stdio.h> #include <ctype.h> #include <signal.h> #define ARGVAL() (*++(*argv) || (--argc && *++argv)) static int n_bits; /* number of bits/code */ static int maxbits = BITS; /* user settable max # bits/code */ static code_int maxcode; /* maximum code, given n_bits */ static code_int maxmaxcode = (code_int)1 << BITS; /* should NEVER generate this code */ #ifdef COMPATIBLE /* But wrong! */ # define MAXCODE(n_bits) ((code_int) 1 << (n_bits) - 1) #else # define MAXCODE(n_bits) (((code_int) 1 << (n_bits)) - 1) #endif /* COMPATIBLE */ static count_int htab [HSIZE]; static unsigned short codetab [HSIZE]; #define HashTabOf(i) htab[i] #define CodeTabOf(i) codetab[i] static code_int hsize = HSIZE; /* for dynamic table sizing */ static count_int fsize; /* * To save much memory, we overlay the table used by compress() with those * used by decompress(). The tab_prefix table is the same size and type * as the codetab. The tab_suffix table needs 2**BITS characters. We * get this from the beginning of htab. The output stack uses the rest * of htab, and contains characters. There is plenty of room for any * possible stack (stack used to be 8000 characters). */ #define tab_prefixof(i) CodeTabOf(i) #define tab_suffixof(i) ((char_type *)(htab))[i] #define de_stack ((char_type *)&tab_suffixof((code_int)1<<BITS)) static code_int free_ent = 0; /* first unused entry */ static int exit_stat = 0; /* * block compression parameters -- after all codes are used up, * and compression rate changes, start over. */ static int clear_flg = 0; static int offset; static long int in_count = 1; /* length of input */ static long int out_count = 0; /* # of codes output (for debugging) */ /* * compress stdin to stdout * * Algorithm: use open addressing double hashing (no chaining) on the * prefix code / next character combination. We do a variant of Knuth's * algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime * secondary probe. Here, the modular division first probe is gives way * to a faster exclusive-or manipulation. Also do block compression with * an adaptive reset, whereby the code table is cleared when the compression * ratio decreases, but after the table fills. The variable-length output * codes are re-sized at this point, and a special CLEAR code is generated * for the decompressor. Late addition: construct the table according to * file size for noticeable speed improvement on small files. Please direct * questions about this implementation to ames!jaw. */ static int g_init_bits; static FILE *g_outfile; static int ClearCode; static int EOFCode; compress( init_bits, outfile, ReadValue ) int init_bits; FILE *outfile; ifunptr ReadValue; { register long fcode; register code_int i = 0; register int c; register code_int ent; register code_int disp; register code_int hsize_reg; register int hshift; /* * Set up the globals: g_init_bits - initial number of bits * g_outfile - pointer to output file */ g_init_bits = init_bits; g_outfile = outfile; /* * Set up the necessary values */ offset = 0; out_count = 0; clear_flg = 0; in_count = 1; maxcode = MAXCODE(n_bits = g_init_bits); ClearCode = (1 << (init_bits - 1)); EOFCode = ClearCode + 1; free_ent = ClearCode + 2; char_init(); ent = GIFNextPixel( ReadValue ); hshift = 0; for ( fcode = (long) hsize; fcode < 65536L; fcode *= 2L ) hshift++; hshift = 8 - hshift; /* set hash code range bound */ hsize_reg = hsize; cl_hash( (count_int) hsize_reg); /* clear hash table */ output( (code_int)ClearCode ); #ifdef SIGNED_COMPARE_SLOW while ( (c = GIFNextPixel( ReadValue )) != (unsigned) EOF ) { #else while ( (c = GIFNextPixel( ReadValue )) != EOF ) { #endif in_count++; fcode = (long) (((long) c << maxbits) + ent); i = (((code_int)c << hshift) ^ ent); /* xor hashing */ if ( HashTabOf (i) == fcode ) { ent = CodeTabOf (i); continue; } else if ( (long)HashTabOf (i) < 0 ) /* empty slot */ goto nomatch; disp = hsize_reg - i; /* secondary hash (after G. Knott) */ if ( i == 0 ) disp = 1; probe: if ( (i -= disp) < 0 ) i += hsize_reg; if ( HashTabOf (i) == fcode ) { ent = CodeTabOf (i); continue; } if ( (long)HashTabOf (i) > 0 ) goto probe; nomatch: output ( (code_int) ent ); out_count++; ent = c; #ifdef SIGNED_COMPARE_SLOW if ( (unsigned) free_ent < (unsigned) maxmaxcode) { #else if ( free_ent < maxmaxcode ) { #endif CodeTabOf (i) = free_ent++; /* code -> hashtable */ HashTabOf (i) = fcode; } else cl_block(); } /* * Put out the final code. */ output( (code_int)ent ); out_count++; output( (code_int) EOFCode ); return; } /***************************************************************** * TAG( output ) * * Output the given code. * Inputs: * code: A n_bits-bit integer. If == -1, then EOF. This assumes * that n_bits =< (long)wordsize - 1. * Outputs: * Outputs code to the file. * Assumptions: * Chars are 8 bits long. * Algorithm: * Maintain a BITS character long buffer (so that 8 codes will * fit in it exactly). Use the VAX insv instruction to insert each * code in turn. When the buffer fills up empty it and start over. */ static unsigned long cur_accum = 0; static int cur_bits = 0; static unsigned long masks[] = { 0x0000, 0x0001, 0x0003, 0x0007, 0x000F, 0x001F, 0x003F, 0x007F, 0x00FF, 0x01FF, 0x03FF, 0x07FF, 0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF }; static output( code ) code_int code; { cur_accum &= masks[ cur_bits ]; if( cur_bits > 0 ) cur_accum |= ((long)code << cur_bits); else cur_accum = code; cur_bits += n_bits; while( cur_bits >= 8 ) { char_out( (unsigned int)(cur_accum & 0xff) ); cur_accum >>= 8; cur_bits -= 8; } /* * If the next entry is going to be too big for the code size, * then increase it, if possible. */ if ( free_ent > maxcode || clear_flg ) { if( clear_flg ) { maxcode = MAXCODE (n_bits = g_init_bits); clear_flg = 0; } else { n_bits++; if ( n_bits == maxbits ) maxcode = maxmaxcode; else maxcode = MAXCODE(n_bits); } } if( code == EOFCode ) { /* * At EOF, write the rest of the buffer. */ while( cur_bits > 0 ) { char_out( (unsigned int)(cur_accum & 0xff) ); cur_accum >>= 8; cur_bits -= 8; } flush_char(); fflush( g_outfile ); if( ferror( g_outfile ) ) writeerr(); } } /* * Clear out the hash table */ static cl_block () /* table clear for block compress */ { cl_hash ( (count_int) hsize ); free_ent = ClearCode + 2; clear_flg = 1; output( (code_int)ClearCode ); } static cl_hash(hsize) /* reset code table */ register count_int hsize; { register count_int *htab_p = htab+hsize; register long i; register long m1 = -1; i = hsize - 16; do { /* might use Sys V memset(3) here */ *(htab_p-16) = m1; *(htab_p-15) = m1; *(htab_p-14) = m1; *(htab_p-13) = m1; *(htab_p-12) = m1; *(htab_p-11) = m1; *(htab_p-10) = m1; *(htab_p-9) = m1; *(htab_p-8) = m1; *(htab_p-7) = m1; *(htab_p-6) = m1; *(htab_p-5) = m1; *(htab_p-4) = m1; *(htab_p-3) = m1; *(htab_p-2) = m1; *(htab_p-1) = m1; htab_p -= 16; } while ((i -= 16) >= 0); for ( i += 16; i > 0; i-- ) *--htab_p = m1; } static writeerr() { printf( "error writing output file\n" ); exit(1); } /****************************************************************************** * * GIF Specific routines * ******************************************************************************/ /* * Number of characters so far in this 'packet' */ static int a_count; /* * Set up the 'byte output' routine */ static char_init() { a_count = 0; } /* * Define the storage for the packet accumulator */ static char accum[ 256 ]; /* * Add a character to the end of the current packet, and if it is 254 * characters, flush the packet to disk. */ static char_out( c ) int c; { accum[ a_count++ ] = c; if( a_count >= 254 ) flush_char(); } /* * Flush the packet to disk, and reset the accumulator */ static flush_char() { if( a_count > 0 ) { fputc( a_count, g_outfile ); fwrite( accum, 1, a_count, g_outfile ); a_count = 0; } } /* The End */ @//E*O*F gifcompr.c// chmod u=rw,g=r,o=r gifcompr.c echo x - gifencod.c sed 's/^@//' > "gifencod.c" <<'@//E*O*F gifencod.c//' /***************************************************************************** * * GIFENCODE.C - GIF Image compression interface * * GIFEncode( FName, GHeight, GWidth, GInterlace, Background, * BitsPerPixel, Red, Green, Blue, GetPixel ) * *****************************************************************************/ #include <stdio.h> /* * Pointer to function returning an int */ typedef int (* ifunptr)(); #define TRUE 1 #define FALSE 0 static int Width, Height; static int curx, cury; static long CountDown; static int Pass = 0; static int Interlace; /* * Bump the 'curx' and 'cury' to point to the next pixel */ static BumpPixel() { /* * Bump the current X position */ curx++; /* * If we are at the end of a scan line, set curx back to the beginning * If we are interlaced, bump the cury to the appropriate spot, * otherwise, just increment it. */ if( curx == Width ) { curx = 0; if( !Interlace ) cury++; else { switch( Pass ) { case 0: cury += 8; if( cury >= Height ) { Pass++; cury = 4; } break; case 1: cury += 8; if( cury >= Height ) { Pass++; cury = 2; } break; case 2: cury += 4; if( cury >= Height ) { Pass++; cury = 1; } break; case 3: cury += 2; break; } } } } /* * Return the next pixel from the image */ GIFNextPixel( getpixel ) ifunptr getpixel; { int r; if( CountDown == 0 ) return EOF; CountDown--; r = ( * getpixel )( curx, cury ); BumpPixel(); return r; } /* public */ GIFEncode( FName, GWidth, GHeight, GInterlace, Background, BitsPerPixel, Red, Green, Blue, GetPixel ) char *FName; int GWidth, GHeight; int GInterlace; int Background; int BitsPerPixel; int Red[], Green[], Blue[]; ifunptr GetPixel; { FILE *fp; int B; int RWidth, RHeight; int LeftOfs, TopOfs; int Resolution; int ColorMapSize; int InitCodeSize; int i; Interlace = GInterlace; ColorMapSize = 1 << BitsPerPixel; RWidth = Width = GWidth; RHeight = Height = GHeight; LeftOfs = TopOfs = 0; Resolution = BitsPerPixel; /* * Calculate number of bits we are expecting */ CountDown = (long)Width * (long)Height; /* * Indicate which pass we are on (if interlace) */ Pass = 0; /* * The initial code size */ if( BitsPerPixel <= 1 ) InitCodeSize = 2; else InitCodeSize = BitsPerPixel; /* * Set up the current x and y position */ curx = cury = 0; /* * Open the GIF file for binary write */ fp = fopen( FName, "wb" ); if( fp == (FILE *)0 ) { printf( "error: could not open output file\n" ); exit(1); } /* * Write the Magic header */ fwrite( "GIF87a", 1, 6, fp ); /* * Write out the screen width and height */ Putword( RWidth, fp ); Putword( RHeight, fp ); /* * Indicate that there is a global colour map */ B = 0x80; /* Yes, there is a color map */ /* * OR in the resolution */ B |= (Resolution - 1) << 5; /* * OR in the Bits per Pixel */ B |= (BitsPerPixel - 1); /* * Write it out */ fputc( B, fp ); /* * Write out the Background colour */ fputc( Background, fp ); /* * Byte of 0's (future expansion) */ fputc( 0, fp ); /* * Write out the Global Colour Map */ for( i=0; i<ColorMapSize; i++ ) { fputc( Red[i], fp ); fputc( Green[i], fp ); fputc( Blue[i], fp ); } /* * Write an Image separator */ fputc( ',', fp ); /* * Write the Image header */ Putword( LeftOfs, fp ); Putword( TopOfs, fp ); Putword( Width, fp ); Putword( Height, fp ); /* * Write out whether or not the image is interlaced */ if( Interlace ) fputc( 0x40, fp ); else fputc( 0x00, fp ); /* * Write out the initial code size */ fputc( InitCodeSize, fp ); /* * Go and actually compress the data */ compress( InitCodeSize+1, fp, GetPixel ); /* * Write out a Zero-length packet (to end the series) */ fputc( 0, fp ); /* * Write the GIF file terminator */ fputc( ';', fp ); /* * And close the file */ fclose( fp ); } /* * Write out a word to the GIF file */ static Putword( w, fp ) int w; FILE *fp; { fputc( w & 0xff, fp ); fputc( (w / 256) & 0xff, fp ); } @//E*O*F gifencod.c// chmod u=rw,g=r,o=r gifencod.c exit 0