png.c: Use palette for file size savings

backend/png.c

@@ -2,7 +2,7 @@
 
 /*
     libzint - the open source barcode library
-    Copyright (C) 2009-2017 Robin Stuart <rstuart114@gmail.com>
+    Copyright (C) 2009-2021 Robin Stuart <rstuart114@gmail.com>
 
     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
@@ -37,8 +37,6 @@
 #include <io.h>
 #include <malloc.h>
 #endif
-#include <stdlib.h>
-#include <string.h>
 #include "common.h"
 
 #ifndef NO_PNG
@@ -72,37 +70,47 @@ static void writepng_error_handler(png_structp png_ptr, png_const_charp msg) {
     longjmp(graphic->jmpbuf, 1);
 }
 
+/* Guestimate best compression strategy */
+static int guess_compression_strategy(struct zint_symbol *symbol, unsigned char *pixelbuf) {
+    (void)pixelbuf;
+
+    /* TODO: Do properly */
+
+    /* It seems the best choice for typical barcode pngs is one of Z_DEFAULT_STRATEGY and Z_FILTERED */
+
+    /* Some guesses */
+    if (symbol->symbology == BARCODE_MAXICODE) {
+        return Z_DEFAULT_STRATEGY;
+    }
+    if (symbol->symbology == BARCODE_AZTEC && symbol->bitmap_width <= 30) {
+        return Z_DEFAULT_STRATEGY;
+    }
+
+    /* Z_FILTERED seems to work better for slightly more barcodes+data so default to that */
+    return Z_FILTERED;
+}
+
 INTERNAL int png_pixel_plot(struct zint_symbol *symbol, unsigned char *pixelbuf) {
     struct mainprog_info_type wpng_info;
     struct mainprog_info_type *graphic;
     png_structp png_ptr;
     png_infop info_ptr;
+    int i;
     int row, column;
-    unsigned char fg[4], bg[4];
-    unsigned char white[4] =   { 0xff, 0xff, 0xff, 0xff };
-    unsigned char cyan[4] =    {    0, 0xff, 0xff, 0xff };
-    unsigned char blue[4] =    {    0,    0, 0xff, 0xff };
-    unsigned char magenta[4] = { 0xff,    0, 0xff, 0xff };
-    unsigned char red[4] =     { 0xff,    0,    0, 0xff };
-    unsigned char yellow[4] =  { 0xff, 0xff,    0, 0xff };
-    unsigned char green[4] =   {    0, 0xff,    0, 0xff };
-    unsigned char black[4] =   {    0,    0,    0, 0xff };
-    unsigned char *map[91] = {
-        NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, /* 0x00-0F */
-        NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, /* 0x10-1F */
-        NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, /* 0x20-2F */
-        bg, fg, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, /* 0-9 */
-        NULL, NULL, NULL, NULL, NULL, NULL, NULL, /* :;<=>?@ */
-        NULL, blue, cyan, NULL, NULL, NULL, green, NULL, NULL, NULL, black, NULL, magenta, /* A-M */
-        NULL, NULL, NULL, NULL, red, NULL, NULL, NULL, NULL, white, NULL, yellow, NULL /* N-Z */
-    };
-    int use_alpha, incr;
-    unsigned char *image_data;
+    png_color bg, fg;
+    unsigned char bg_alpha, fg_alpha;
+    unsigned char map[128];
+    png_color palette[32];
+    int num_palette = 0;
+    unsigned char trans_alpha[32];
+    int num_trans = 0;
+    int bit_depth;
+    int compression_strategy;
 
 #ifndef _MSC_VER
-    unsigned char outdata[symbol->bitmap_width * 4];
+    unsigned char outdata[symbol->bitmap_width];
 #else
-    unsigned char* outdata = (unsigned char*) _alloca(symbol->bitmap_width * 4);
+    unsigned char* outdata = (unsigned char*) _alloca(symbol->bitmap_width);
 #endif
 
     graphic = &wpng_info;
@@ -110,28 +118,101 @@ INTERNAL int png_pixel_plot(struct zint_symbol *symbol, unsigned char *pixelbuf)
     graphic->width = symbol->bitmap_width;
     graphic->height = symbol->bitmap_height;
 
-    fg[0] = (16 * ctoi(symbol->fgcolour[0])) + ctoi(symbol->fgcolour[1]);
-    fg[1] = (16 * ctoi(symbol->fgcolour[2])) + ctoi(symbol->fgcolour[3]);
-    fg[2] = (16 * ctoi(symbol->fgcolour[4])) + ctoi(symbol->fgcolour[5]);
-    bg[0] = (16 * ctoi(symbol->bgcolour[0])) + ctoi(symbol->bgcolour[1]);
-    bg[1] = (16 * ctoi(symbol->bgcolour[2])) + ctoi(symbol->bgcolour[3]);
-    bg[2] = (16 * ctoi(symbol->bgcolour[4])) + ctoi(symbol->bgcolour[5]);
+    fg.red = (16 * ctoi(symbol->fgcolour[0])) + ctoi(symbol->fgcolour[1]);
+    fg.green = (16 * ctoi(symbol->fgcolour[2])) + ctoi(symbol->fgcolour[3]);
+    fg.blue = (16 * ctoi(symbol->fgcolour[4])) + ctoi(symbol->fgcolour[5]);
+    bg.red = (16 * ctoi(symbol->bgcolour[0])) + ctoi(symbol->bgcolour[1]);
+    bg.green = (16 * ctoi(symbol->bgcolour[2])) + ctoi(symbol->bgcolour[3]);
+    bg.blue = (16 * ctoi(symbol->bgcolour[4])) + ctoi(symbol->bgcolour[5]);
 
-    use_alpha = 0;
-    
     if (strlen(symbol->fgcolour) > 6) {
-        fg[3] = (16 * ctoi(symbol->fgcolour[6])) + ctoi(symbol->fgcolour[7]);
-        white[3] = cyan[3] = blue[3] = magenta[3] = red[3] = yellow[3] = green[3] = black[3] = fg[3];
-        if (fg[3] != 0xff) use_alpha = 1;
+        fg_alpha = (16 * ctoi(symbol->fgcolour[6])) + ctoi(symbol->fgcolour[7]);
     } else {
-        fg[3] = 0xff;
+        fg_alpha = 0xff;
     }
-    
+
     if (strlen(symbol->bgcolour) > 6) {
-        bg[3] = (16 * ctoi(symbol->bgcolour[6])) + ctoi(symbol->bgcolour[7]);
-        if (bg[3] != 0xff) use_alpha = 1;
+        bg_alpha = (16 * ctoi(symbol->bgcolour[6])) + ctoi(symbol->bgcolour[7]);
     } else {
-        bg[3] = 0xff;
+        bg_alpha = 0xff;
+    }
+
+    if (symbol->symbology == BARCODE_ULTRA) {
+        static const int ultra_chars[8] = { 'W', 'C', 'B', 'M', 'R', 'Y', 'G', 'K' };
+        static png_color ultra_colours[8] = {
+            { 0xff, 0xff, 0xff, }, /* White */
+            {    0, 0xff, 0xff, }, /* Cyan */
+            {    0,    0, 0xff, }, /* Blue */
+            { 0xff,    0, 0xff, }, /* Magenta */
+            { 0xff,    0,    0, }, /* Red */
+            { 0xff, 0xff,    0, }, /* Yellow */
+            {    0, 0xff,    0, }, /* Green */
+            {    0,    0,    0, }, /* Black */
+        };
+        for (i = 0; i < 8; i++) {
+            map[ultra_chars[i]] = i;
+            palette[i] = ultra_colours[i];
+            if (fg_alpha != 0xff) {
+                trans_alpha[i] = fg_alpha;
+            }
+        }
+        num_palette = 8;
+        if (fg_alpha != 0xff) {
+            num_trans = 8;
+        }
+
+        /* For Ultracode, have background only if have whitespace/quiet zones */
+        if (pixelbuf[0] == '0' || pixelbuf[symbol->bitmap_width - 1] == '0'
+                || pixelbuf[symbol->bitmap_height * (symbol->bitmap_width - 1)] == '0'
+                || pixelbuf[symbol->bitmap_height * symbol->bitmap_width - 1] == '0') {
+            /* Check whether can re-use white */
+            if (bg.red == 0xff && bg.green == 0xff && bg.blue == 0xff && bg_alpha == fg_alpha) {
+                map['0'] = 0; /* Re-use white */
+            } else {
+                if (bg_alpha == 0xff || fg_alpha != 0xff) {
+                    /* No alpha or have foreground alpha - add to end */
+                    map['0'] = num_palette;
+                    palette[num_palette++] = bg;
+                } else {
+                    /* Alpha and no foreground alpha - add to front & move white to end */
+                    map['0'] = 0;
+                    palette[0] = bg;
+                    map['W'] = num_palette;
+                    palette[num_palette++] = ultra_colours[0];
+                }
+                if (bg_alpha != 0xff) {
+                    trans_alpha[num_trans++] = bg_alpha;
+                }
+            }
+        }
+    } else {
+        int bg_idx = 0, fg_idx = 1;
+        /* Do alphas first so can swop indexes if background not alpha */
+        if (bg_alpha != 0xff) {
+            trans_alpha[num_trans++] = bg_alpha;
+        }
+        if (fg_alpha != 0xff) {
+            trans_alpha[num_trans++] = fg_alpha;
+            if (num_trans == 1) {
+                /* Only foreground has alpha so swop indexes - saves a byte! */
+                bg_idx = 1;
+                fg_idx = 0;
+            }
+        }
+
+        map['0'] = bg_idx;
+        palette[bg_idx] = bg;
+        map['1'] = fg_idx;
+        palette[fg_idx] = fg;
+        num_palette = 2;
+    }
+
+    if (num_palette <= 2) {
+        bit_depth = 1;
+    } else if (num_palette <= 16) {
+        bit_depth = 4;
+    } else {
+        bit_depth = 8;
     }
 
     /* Open output file in binary mode */
@@ -177,32 +258,64 @@ INTERNAL int png_pixel_plot(struct zint_symbol *symbol, unsigned char *pixelbuf)
     /* set compression */
     png_set_compression_level(png_ptr, 9);
 
+    /* Compression strategy can make a difference */
+    compression_strategy = guess_compression_strategy(symbol, pixelbuf);
+    if (compression_strategy != Z_DEFAULT_STRATEGY) {
+        png_set_compression_strategy(png_ptr, compression_strategy);
+    }
+
     /* set Header block */
-    if (use_alpha)
-        png_set_IHDR(png_ptr, info_ptr, graphic->width, graphic->height,
-                8, PNG_COLOR_TYPE_RGBA, PNG_INTERLACE_NONE,
-                PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
-    else
-        png_set_IHDR(png_ptr, info_ptr, graphic->width, graphic->height,
-                8, PNG_COLOR_TYPE_RGB, PNG_INTERLACE_NONE,
-                PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
+    png_set_IHDR(png_ptr, info_ptr, graphic->width, graphic->height,
+            bit_depth, PNG_COLOR_TYPE_PALETTE, PNG_INTERLACE_NONE,
+            PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
+
+    png_set_PLTE(png_ptr, info_ptr, palette, num_palette);
+    if (num_trans) {
+        png_set_tRNS(png_ptr, info_ptr, trans_alpha, num_trans, NULL);
+    }
+
     /* write all chunks up to (but not including) first IDAT */
     png_write_info(png_ptr, info_ptr);
 
-    /* set up the transformations:  for now, just pack low-bit-depth pixels
-    into bytes (one, two or four pixels per byte) */
-    png_set_packing(png_ptr);
-
     /* Pixel Plotting */
-    incr = use_alpha ? 4 : 3;
-    for (row = 0; row < symbol->bitmap_height; row++) {
-        unsigned char *pb = pixelbuf + symbol->bitmap_width * row;
-        image_data = outdata;
-        for (column = 0; column < symbol->bitmap_width; column++, pb++, image_data += incr) {
-            memcpy(image_data, map[*pb], incr);
+    if (bit_depth == 1) {
+        for (row = 0; row < symbol->bitmap_height; row++) {
+            unsigned char *pb = pixelbuf + symbol->bitmap_width * row;
+            unsigned char *image_data = outdata;
+            for (column = 0; column < symbol->bitmap_width; column += 8, image_data++) {
+                unsigned char byte = 0;
+                for (i = 0; i < 8 && column + i < symbol->bitmap_width; i++, pb++) {
+                    byte |= map[*pb] << (7 - i);
+                }
+                *image_data = byte;
+            }
+            /* write row contents to file */
+            png_write_row(png_ptr, outdata);
+        }
+    } else if (bit_depth == 4) {
+        for (row = 0; row < symbol->bitmap_height; row++) {
+            unsigned char *pb = pixelbuf + symbol->bitmap_width * row;
+            unsigned char *image_data = outdata;
+            for (column = 0; column < symbol->bitmap_width; column += 2, image_data++) {
+                unsigned char byte = 0;
+                for (i = 0; i < 2 && column + i < symbol->bitmap_width; i++, pb++) {
+                    byte |= map[*pb] << (i * 4);
+                }
+                *image_data = byte;
+            }
+            /* write row contents to file */
+            png_write_row(png_ptr, outdata);
+        }
+    } else { /* Bit depth 8 */
+        for (row = 0; row < symbol->bitmap_height; row++) {
+            unsigned char *pb = pixelbuf + symbol->bitmap_width * row;
+            unsigned char *image_data = outdata;
+            for (column = 0; column < symbol->bitmap_width; column++, pb++, image_data++) {
+                *image_data = map[*pb];
+            }
+            /* write row contents to file */
+            png_write_row(png_ptr, outdata);
         }
-        /* write row contents to file */
-        png_write_row(png_ptr, outdata);
     }
 
     /* End the file */
@@ -215,6 +328,7 @@ INTERNAL int png_pixel_plot(struct zint_symbol *symbol, unsigned char *pixelbuf)
     } else {
         fclose(wpng_info.outfile);
     }
+
     return 0;
 }
 #endif /* NO_PNG */

backend/tests/test_png.c

@@ -1,6 +1,6 @@
 /*
     libzint - the open source barcode library
-    Copyright (C) 2020 Robin Stuart <rstuart114@gmail.com>
+    Copyright (C) 2020 - 2021 Robin Stuart <rstuart114@gmail.com>
 
     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
@@ -164,7 +164,11 @@ static void test_print(int index, int generate, int debug) {
         /* 29*/ { BARCODE_POSTNET, -1, -1, -1, -1, -1, -1, 0, 3.5, "", "", "12345", "", "../data/png/postnet_zip.png", "300 dpi, using 1/43in X, 300 / 43 / 2 = ~3.5 scale" },
         /* 30*/ { BARCODE_PDF417, -1, -1, -1, -1, -1, -1, 0, 0, "", "CFCECDCC", "12345", "", "../data/png/pdf417_bgalpha.png", "" },
         /* 31*/ { BARCODE_PDF417, -1, -1, -1, -1, -1, -1, 0, 0, "30313233", "", "12345", "", "../data/png/pdf417_fgalpha.png", "" },
-        /* 32*/ { BARCODE_ULTRA, -1, -1, 2, -1, -1, -1, 0, 0, "0000007F", "FF000033", "12345", "", "../data/png/ultra_alpha.png", "" },
+        /* 32*/ { BARCODE_PDF417, -1, -1, -1, -1, -1, -1, 0, 0, "20212244", "CFCECDCC", "12345", "", "../data/png/pdf417_bgfgalpha.png", "" },
+        /* 33*/ { BARCODE_ULTRA, -1, -1, 2, -1, -1, -1, 0, 0, "0000007F", "FF000033", "12345", "", "../data/png/ultra_bgfgalpha.png", "" },
+        /* 34*/ { BARCODE_ULTRA, -1, -1, 2, -1, -1, -1, 0, 0, "", "FF000033", "12345", "", "../data/png/ultra_bgalpha.png", "" },
+        /* 35*/ { BARCODE_ULTRA, -1, -1, 2, -1, -1, -1, 0, 0, "0000007F", "FF0000", "12345", "", "../data/png/ultra_fgalpha.png", "" },
+        /* 36*/ { BARCODE_ULTRA, -1, -1, -1, -1, -1, -1, 0, 0, "0000007F", "", "12345", "", "../data/png/ultra_fgalpha_nobg.png", "" },
     };
     int data_size = ARRAY_SIZE(data);
 
@@ -242,6 +246,8 @@ static void test_print(int index, int generate, int debug) {
 
             ret = testUtilCmpPngs(symbol->outfile, data[i].expected_file);
             assert_zero(ret, "i:%d %s testUtilCmpPngs(%s, %s) %d != 0\n", i, testUtilBarcodeName(data[i].symbology), symbol->outfile, data[i].expected_file, ret);
+            ret = testUtilCmpBins(symbol->outfile, data[i].expected_file);
+            assert_zero(ret, "i:%d %s testUtilCmpBins(%s, %s) %d != 0\n", i, testUtilBarcodeName(data[i].symbology), symbol->outfile, data[i].expected_file, ret);
             assert_zero(remove(symbol->outfile), "i:%d remove(%s) != 0\n", i, symbol->outfile);
         }
 

backend/tests/test_print.c

@@ -166,6 +166,8 @@ static void test_print(int index, int generate, int debug) {
                 } else if (strcmp(exts[j], "png") == 0) {
                     ret = testUtilCmpPngs(symbol->outfile, expected_file);
                     assert_zero(ret, "i:%d %s testUtilCmpPngs(%s, %s) %d != 0\n", i, testUtilBarcodeName(data[i].symbology), symbol->outfile, expected_file, ret);
+                    ret = testUtilCmpBins(symbol->outfile, expected_file);
+                    assert_zero(ret, "i:%d %s testUtilCmpBins(%s, %s) %d != 0\n", i, testUtilBarcodeName(data[i].symbology), symbol->outfile, expected_file, ret);
                 } else if (strcmp(exts[j], "svg") == 0) {
                     ret = testUtilCmpSvgs(symbol->outfile, expected_file);
                     assert_zero(ret, "i:%d %s testUtilCmpSvgs(%s, %s) %d != 0\n", i, testUtilBarcodeName(data[i].symbology), symbol->outfile, expected_file, ret);