* Add pipi_dither_ediff(), a generic error diffusion dithering algorithm

that uses an image as the error diffusion kernel.

git-svn-id: file:///srv/caca.zoy.org/var/lib/svn/libpipi/trunk@2758 92316355-f0b4-4df1-b90c-862c8a59935f

pipi/Makefile.am

@@ -64,6 +64,7 @@ quantize_sources = \
 	quantize/reduce.c
 
 dither_sources = \
+	dither/ediff.c \
 	dither/floydsteinberg.c \
 	dither/jajuni.c \
 	dither/atkinson.c \

pipi/context.c

@@ -100,6 +100,14 @@ int pipi_command(pipi_context_t *ctx, char const *cmd, ...)
             dst = pipi_dither_ostromoukhov(src, 0);
         else if(!strcmp(method, "sost"))
             dst = pipi_dither_ostromoukhov(src, 1);
+        else if(!strcmp(method, "ediff"))
+        {
+            if(ctx->nimages < 2)
+                return -1;
+            dst = pipi_dither_ediff(ctx->images[ctx->nimages - 2], src, 0);
+            pipi_free(ctx->images[ctx->nimages - 2]);
+            ctx->nimages--;
+        }
         else if(!strcmp(method, "ordered"))
         {
             if(ctx->nimages < 2)

pipi/dither/ediff.c

@@ -0,0 +1,84 @@
+/*
+ *  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.
+ */
+
+/*
+ * ed.c: generic error diffusion functions
+ */
+
+#include "config.h"
+#include "common.h"
+
+#include "pipi.h"
+#include "pipi_internals.h"
+
+/* Perform a generic error diffusion dithering. The first non-zero
+ * element in ker is treated as the current pixel. All other non-zero
+ * elements are the error diffusion coefficients. */
+pipi_image_t *pipi_dither_ediff(pipi_image_t *img, pipi_image_t *ker,
+                                pipi_scan_t scan)
+{
+    pipi_image_t *dst;
+    pipi_pixels_t *dstp, *kerp;
+    float *dstdata, *kerdata;
+    int x, y, w, h, i, j, kx, kw, kh;
+
+    w = img->w;
+    h = img->h;
+    kw = ker->w;
+    kh = ker->h;
+
+    dst = pipi_copy(img);
+    dstp = pipi_getpixels(dst, PIPI_PIXELS_Y_F);
+    dstdata = (float *)dstp->pixels;
+
+    kerp = pipi_getpixels(ker, PIPI_PIXELS_Y_F);
+    kerdata = (float *)kerp->pixels;
+    for(kx = 0; kx < kw; kx++)
+        if(kerdata[kx] > 0)
+            break;
+
+    for(y = 0; y < h; y++)
+    {
+        int reverse = (y & 1) && (scan == PIPI_SCAN_SERPENTINE);
+
+        for(x = 0; x < w; x++)
+        {
+            float p, q, e;
+            int x2 = reverse ? w - 1 - x : x;
+            int s = reverse ? -1 : 1;
+
+            p = dstdata[y * w + x2];
+            q = p < 0.5 ? 0. : 1.;
+            dstdata[y * w + x2] = q;
+
+            e = (p - q);
+
+            for(j = 0; j < kh && y < h - j; j++)
+                for(i = 0; i < kw; i++)
+                {
+                    if(j == 0 && i <= kx)
+                        continue;
+
+                    if(x + i - kx < 0 || x + i - kx >= w)
+                        continue;
+
+                    dstdata[(y + j) * w + x2 + (i - kx) * s]
+                       += e * kerdata[j * kw + i];
+                }
+        }
+    }
+
+    return dst;
+}
+

pipi/pipi.h

@@ -147,6 +147,8 @@ extern int pipi_flood_fill(pipi_image_t *,
 
 extern pipi_image_t *pipi_reduce(pipi_image_t *, int, double const *);
 
+extern pipi_image_t *pipi_dither_ediff(pipi_image_t *, pipi_image_t *,
+                                       pipi_scan_t);
 extern pipi_image_t *pipi_dither_floydsteinberg(pipi_image_t *, pipi_scan_t);
 extern pipi_image_t *pipi_dither_jajuni(pipi_image_t *, pipi_scan_t);
 extern pipi_image_t *pipi_dither_atkinson(pipi_image_t *, pipi_scan_t);