Input/output files

README.md

@@ -6,14 +6,14 @@ The goal of this tool is to make RGB/RGBA PNG images more compressible, assuming
 
 ##Usage
 
- posterize [ -v ] [ -d ] [ -q <quality> ] [ levels ] < input.png > output.png
+ posterize [ -v ] [ -d ] [ -Q <quality> ] [ levels ] -- [ input.png ] [ output.png ]
 
 * `levels` — Number of levels to use (2-255). Lower number gives worse quality, but smaller file.
-* `-q num` — Picks minimum number of levels needed to achieve given quality. `num` is quality 0-100 (100 is best, similar to JPEG). Number of levels is optional if quality is specified.
+* `-Q num` — Picks minimum number of levels needed to achieve given quality. `num` is quality 0-100 (100 is best, similar to JPEG). Number of levels is optional if quality is specified.
 * `-d` — Enables simple ordered dithering.
 * `-v` — Verbose output. Prints mean square error (MSE) caused by posterization.
 
-Only stdin/stdout is supported.
+If input/output files are not specified then stdin/stdout is used respectively.
 
 Posterized images can be further compressed using [PNGOUT](http:https://www.jonof.id.au/kenutils) or similar. Try [ImageOptim](http:https://imageoptim.com).
 

posterize.c

@@ -355,12 +355,12 @@ static void usage(const char *exepath)
  const char *name = strrchr(exepath, '/');
  if (name) name++; else name = exepath;
  fprintf(stderr, "Median Cut PNG Posterizer 1.6 (2013).\n" \
- "Usage: %s [-vd] [-Q <quality>] [levels]\n\n" \
+ "Usage: %s [-vd] [-Q <quality>] [levels] [input file] [output file]\n\n" \
  "Specify number of levels (2-255) or quality (10-100).\n" \
  "-d enables dithering\n" \
  "-v verbose output (to stderr)\n\n" \
- "Image is always read from stdin and written to stdout.\n"
- "%s -d 16 < in.png > out.png\n", name, name);
+ "If files are not specified stdin and stdout is used.\n"
+ "%s -Q 95 in.png out.png\n", name, name);
 }
 
 // performs voronoi iteration (mapping histogram to palette and creating new palette from remapped values)
@@ -457,7 +457,26 @@ int main(int argc, char *argv[])
  }
  }
 
- if (argc != argn || maxlevels < 2 || maxlevels > 255) {
+ if (maxlevels < 2 || maxlevels > 255) {
+ usage(argv[0]);
+ return 1;
+ }
+
+ FILE *input = stdin;
+ const char *input_name = "stdin";
+ if (argn < argc && 0 != strcmp("-",argv[argn])) {
+ input_name = argv[argn++];
+ input = fopen(input_name, "rb");
+ }
+
+ FILE *output = stdout;
+ const char *output_name = "stdout";
+ if (argn < argc && 0 != strcmp("-",argv[argn])) {
+ output_name = argv[argn++];
+ output = fopen(output_name, "wb");
+ }
+
+ if (argn != argc) {
  usage(argv[0]);
  return 1;
  }
@@ -468,18 +487,21 @@ int main(int argc, char *argv[])
  png24_image img;
  pngquant_error retval;
 
- if ((retval = rwpng_read_image24(stdin, &img))) {
- fprintf(stderr, "Error: cannot read PNG from stdin\n");
+ if ((retval = rwpng_read_image24(input, &img))) {
+ fprintf(stderr, "Error: cannot read PNG from %s\n", input_name);
  return retval;
  }
+ if (input != stdin) fclose(input);
+
  image_gamma = 1.0/img.gamma;
 
  posterize(&img, maxlevels, maxerror, dither, verbose);
 
- if ((retval = rwpng_write_image24(stdout, &img))) {
- fprintf(stderr, "Error: cannot write PNG to stdout\n");
+ if ((retval = rwpng_write_image24(output, &img))) {
+ fprintf(stderr, "Error: cannot write PNG to %s\n", output_name);
  return retval;
  }
+ if (output != stdout) fclose(output);
 
  return 0;
 }

rwpng.c

@@ -209,6 +209,8 @@ pngquant_error rwpng_read_image24_libpng(FILE *infile, png24_image *mainprog_ptr
 
 pngquant_error rwpng_read_image24(FILE *infile, png24_image *input_image_p)
 {
+ if (!infile) return READ_ERROR;
+
 #if USE_COCOA
  return rwpng_read_image24_cocoa(infile, input_image_p);
 #else
@@ -219,8 +221,9 @@ pngquant_error rwpng_read_image24(FILE *infile, png24_image *input_image_p)
 
 static pngquant_error rwpng_write_image_init(rwpng_png_image *mainprog_ptr, png_structpp png_ptr_p, png_infopp info_ptr_p, FILE *outfile, int fast_compression)
 {
- /* could also replace libpng warning-handler (final NULL), but no need: */
+ if (!outfile) return CANT_WRITE_ERROR;
 
+ /* could also replace libpng warning-handler (final NULL), but no need: */
  *png_ptr_p = png_create_write_struct(PNG_LIBPNG_VER_STRING, mainprog_ptr, rwpng_error_handler, NULL);
 
  if (!(*png_ptr_p)) {