From 90c7527281aaa2a3b4a05c3380c926ba6b113554 Mon Sep 17 00:00:00 2001
From: sam <sam@92316355-f0b4-4df1-b90c-862c8a59935f>
Date: Sat, 23 Aug 2008 13:07:35 +0000
Subject: [PATCH]   * 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    |  1 +
 pipi/context.c      |  8 +++++
 pipi/dither/ediff.c | 84 +++++++++++++++++++++++++++++++++++++++++++++
 pipi/pipi.h         |  2 ++
 4 files changed, 95 insertions(+)
 create mode 100644 pipi/dither/ediff.c

diff --git a/pipi/Makefile.am b/pipi/Makefile.am
index 7ceb1fd..b332630 100644
--- a/pipi/Makefile.am
+++ b/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 \
diff --git a/pipi/context.c b/pipi/context.c
index 0435d06..e480eae 100644
--- a/pipi/context.c
+++ b/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)
diff --git a/pipi/dither/ediff.c b/pipi/dither/ediff.c
new file mode 100644
index 0000000..5e5ec08
--- /dev/null
+++ b/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;
+}
+
diff --git a/pipi/pipi.h b/pipi/pipi.h
index 840b6ab..90a9794 100644
--- a/pipi/pipi.h
+++ b/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);