* floydsteinberg.c: minor optimisation in the FStein error propagation.

git-svn-id: file:///srv/caca.zoy.org/var/lib/svn/libpipi/trunk@2699 92316355-f0b4-4df1-b90c-862c8a59935f

pipi/dither/floydsteinberg.c

@@ -51,17 +51,17 @@ pipi_image_t *pipi_dither_floydsteinberg(pipi_image_t *img, pipi_scan_t scan)
             dstdata[y * w + x2] = q;
 
             /* FIXME: according to our 2008 paper, [7 4 5 0] is a better
-             * error diffusion kernel for serpentine scan. */
-            e = p - q;
+             * error diffusion kernel for serpentine scan than [7 3 5 1]. */
+            e = (p - q) / 16;
             if(x < w - 1)
-                dstdata[y * w + x2 + s] += e * .4375;
+                dstdata[y * w + x2 + s] += e * 7;
             if(y < h - 1)
             {
                 if(x > 0)
-                    dstdata[(y + 1) * w + x2 - s] += e * .1875;
-                dstdata[(y + 1) * w + x2] += e * .3125;
+                    dstdata[(y + 1) * w + x2 - s] += e * 3;
+                dstdata[(y + 1) * w + x2] += e * 5;
                 if(x < w - 1)
-                    dstdata[(y + 1) * w + x2 + s] += e * .0625;
+                    dstdata[(y + 1) * w + x2 + s] += e;
             }
         }
     }