* autocontrast.c: simple autocontrast filter; does not work very well.

git-svn-id: file:///srv/caca.zoy.org/var/lib/svn/libpipi/trunk@2680 92316355-f0b4-4df1-b90c-862c8a59935f

pipi/Makefile.am

@@ -37,6 +37,7 @@ codec_sources =
 
 # Submodules
 filter_sources = \
+	filter/autocontrast.c \
 	filter/blur.c \
 	filter/convolution.c
 

pipi/filter/autocontrast.c

@@ -0,0 +1,110 @@
+/*
+ *  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.
+ */
+
+/*
+ * autocontrast.c: autocontrast functions
+ * TODO: the current approach is naive; we should use the histogram in order
+ * to decide how to change the contrast.
+ */
+
+#include "config.h"
+#include "common.h"
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <math.h>
+
+#include "pipi.h"
+#include "pipi_internals.h"
+
+pipi_image_t *pipi_autocontrast(pipi_image_t *src)
+{
+    pipi_image_t *dst;
+    pipi_pixels_t *srcp, *dstp;
+    float *srcdata, *dstdata;
+    float min = 1.0, max = 0.0, t;
+    int x, y, w, h, gray;
+
+    w = src->w;
+    h = src->h;
+
+    gray = (src->last_modified == PIPI_PIXELS_Y_F);
+
+    srcp = gray ? pipi_getpixels(src, PIPI_PIXELS_Y_F)
+                : pipi_getpixels(src, PIPI_PIXELS_RGBA_F);
+    srcdata = (float *)srcp->pixels;
+
+    for(y = 0; y < h; y++)
+    {
+        for(x = 0; x < w; x++)
+        {
+            if(gray)
+            {
+                if(srcdata[y * w + x] < min)
+                    min = srcdata[y * w + x];
+                if(srcdata[y * w + x] > max)
+                    max = srcdata[y * w + x];
+            }
+            else
+            {
+                if(srcdata[4 * (y * w + x)] < min)
+                    min = srcdata[4 * (y * w + x)];
+                if(srcdata[4 * (y * w + x)] > max)
+                    max = srcdata[4 * (y * w + x)];
+                if(srcdata[4 * (y * w + x) + 1] < min)
+                    min = srcdata[4 * (y * w + x) + 1];
+                if(srcdata[4 * (y * w + x) + 1] > max)
+                    max = srcdata[4 * (y * w + x) + 1];
+                if(srcdata[4 * (y * w + x) + 2] < min)
+                    min = srcdata[4 * (y * w + x) + 2];
+                if(srcdata[4 * (y * w + x) + 2] > max)
+                    max = srcdata[4 * (y * w + x) + 2];
+            }
+        }
+    }
+
+    if(min >= max)
+        return pipi_copy(src);
+
+    t = 1. / (max - min);
+
+    dst = pipi_new(w, h);
+    dstp = gray ? pipi_getpixels(dst, PIPI_PIXELS_Y_F)
+                : pipi_getpixels(dst, PIPI_PIXELS_RGBA_F);
+    dstdata = (float *)dstp->pixels;
+
+    for(y = 0; y < h; y++)
+    {
+        for(x = 0; x < w; x++)
+        {
+            if(gray)
+            {
+                dstdata[y * w + x] = (srcdata[y * w + x] - min) * t;
+            }
+            else
+            {
+                dstdata[4 * (y * w + x)]
+                    = (srcdata[4 * (y * w + x)] - min) * t;
+                dstdata[4 * (y * w + x) + 1]
+                    = (srcdata[4 * (y * w + x) + 1] - min) * t;
+                dstdata[4 * (y * w + x) + 2]
+                    = (srcdata[4 * (y * w + x) + 2] - min) * t;
+            }
+        }
+    }
+
+    return dst;
+}
+

pipi/pipi.h

@@ -81,6 +81,7 @@ extern pipi_image_t *pipi_convolution(pipi_image_t *, int, int, double[]);
 extern pipi_image_t *pipi_gaussian_blur(pipi_image_t *, float);
 extern pipi_image_t *pipi_gaussian_blur_ext(pipi_image_t *,
                                             float, float, float, float);
+extern pipi_image_t *pipi_autocontrast(pipi_image_t *);
 
 extern int pipi_flood_fill(pipi_image_t *,
                            int, int, float, float, float, float);