* random.c: implement random dithering using a deterministic pseudo-RNG.

git-svn-id: file:///srv/caca.zoy.org/var/lib/svn/libpipi/trunk@2671 92316355-f0b4-4df1-b90c-862c8a59935f

examples/dither.c

@@ -17,11 +17,12 @@ int main(int argc, char *argv[])
         fprintf(stderr, "%s: too few arguments\n", argv[0]);
         fprintf(stderr, "Usage: %s <src> <method> <dest>\n", argv[0]);
         fprintf(stderr, "Where <method> is one of:\n");
-        fprintf(stderr, "  1   Floyd-Steinberg (raster)\n");
-        fprintf(stderr, "  2   Floyd-Steinberg (serpentine)\n");
-        fprintf(stderr, "  3   Ostromoukhov (raster)\n");
-        fprintf(stderr, "  4   Ostromoukhov (serpentine)\n");
-        fprintf(stderr, "  5   Direct binary search\n");
+        fprintf(stderr, "  1   random dithering\n");
+        fprintf(stderr, "  2   Floyd-Steinberg (raster)\n");
+        fprintf(stderr, "  3   Floyd-Steinberg (serpentine)\n");
+        fprintf(stderr, "  4   Ostromoukhov (raster)\n");
+        fprintf(stderr, "  5   Ostromoukhov (serpentine)\n");
+        fprintf(stderr, "  6   Direct binary search\n");
         return EXIT_FAILURE;
     }
 
@@ -32,24 +33,27 @@ int main(int argc, char *argv[])
 
     switch(atoi(argv[2]))
     {
-        case 6:
+        case 7:
             newimg = pipi_dither_dbs(img);
             break;
-        case 5:
+        case 6:
             newimg = pipi_dither_ostromoukhov(img, PIPI_SCAN_SERPENTINE);
             break;
-        case 4:
+        case 5:
             newimg = pipi_dither_ostromoukhov(img, PIPI_SCAN_RASTER);
             break;
-        case 3:
+        case 4:
             newimg = pipi_dither_floydsteinberg(img, PIPI_SCAN_SERPENTINE);
             break;
-        case 2:
+        case 3:
             newimg = pipi_dither_floydsteinberg(img, PIPI_SCAN_RASTER);
             break;
+        case 2:
+            newimg = pipi_dither_ordered(img);
+            break;
         case 1:
         default:
-            newimg = pipi_dither_ordered(img);
+            newimg = pipi_dither_random(img);
             break;
     }
 

pipi/Makefile.am

@@ -34,6 +34,7 @@ libpipi_la_SOURCES = \
 	dither/ordered.c \
 	dither/ostromoukhov.c \
 	dither/dbs.c \
+	dither/random.c \
 	$(NULL)
 libpipi_la_CFLAGS = $(codec_cflags)
 libpipi_la_LDFLAGS = $(codec_libs) \

pipi/dither/random.c

@@ -0,0 +1,61 @@
+/*
+ *  libpipi       Proper image processing implementation library
+ *  Copyright (c) 2004-2008 Sam Hocevar <sam@zoy.org>
+ *                All Rights Reserved
+ *
+ *  $Id$
+ *
+ *  This library is free software. It comes without any warranty, to
+ *  the extent permitted by applicable law. You can redistribute it
+ *  and/or modify it under the terms of the Do What The Fuck You Want
+ *  To Public License, Version 2, as published by Sam Hocevar. See
+ *  http://sam.zoy.org/wtfpl/COPYING for more details.
+ */
+
+/*
+ * random.c: random dithering functions
+ */
+
+#include "config.h"
+#include "common.h"
+
+#include "pipi.h"
+#include "pipi_internals.h"
+
+pipi_image_t *pipi_dither_random(pipi_image_t *img)
+{
+    pipi_image_t *dst;
+    pipi_pixels_t *dstp;
+    float *dstdata;
+    unsigned int ctx = 1;
+    int x, y, w, h;
+
+    w = img->w;
+    h = img->h;
+
+    dst = pipi_copy(img);
+    dstp = pipi_getpixels(dst, PIPI_PIXELS_Y_F);
+    dstdata = (float *)dstp->pixels;
+
+    for(y = 0; y < h; y++)
+    {
+        for(x = 0; x < w; x++)
+        {
+            long hi, lo;
+            float p, q;
+
+            hi = ctx / 12773L;
+            lo = ctx % 12773L;
+            ctx = 16807L * lo - 2836L * hi;
+            if(ctx <= 0)
+                ctx += 0x7fffffffL;
+
+            p = dstdata[y * w + x];
+            q = p > (double)((ctx % 65536) / 65535.) ? 1. : 0.;
+            dstdata[y * w + x] = q;
+        }
+    }
+
+    return dst;
+}
+

pipi/pipi.h

@@ -84,6 +84,7 @@ extern pipi_image_t *pipi_gaussian_blur_ext(pipi_image_t *,
 
 extern pipi_image_t *pipi_dither_floydsteinberg(pipi_image_t *, pipi_scan_t);
 extern pipi_image_t *pipi_dither_ordered(pipi_image_t *);
+extern pipi_image_t *pipi_dither_random(pipi_image_t *);
 extern pipi_image_t *pipi_dither_ostromoukhov(pipi_image_t *, pipi_scan_t);
 extern pipi_image_t *pipi_dither_dbs(pipi_image_t *);
 extern void pipi_dither_24to16(pipi_image_t *);