fix ditherImage

brendan-duncan · May 11, 2024 · f12029a · f12029a
1 parent 180bb2c
commit f12029a
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Showing 4 changed files with 38 additions and 22 deletions.
diff --git a/lib/src/filter/dither_image.dart b/lib/src/filter/dither_image.dart
@@ -60,6 +60,7 @@ const _ditherKernels = [
 
 /// Dither an image to reduce banding patterns when reducing the number of
 /// colors.
+/// Derived from http://jsbin.com/iXofIji/2/edit
 Image ditherImage(Image image,
     {Quantizer? quantizer,
     DitherKernel kernel = DitherKernel.floydSteinberg,
@@ -80,24 +81,27 @@ Image ditherImage(Image image,
   final indexedImage =
       Image(width: width, height: height, numChannels: 1, palette: palette);
 
-  final pIter = image.iterator..moveNext();
+  final imageCopy = image.clone();
+
+  final pIter = imageCopy.iterator..moveNext();
 
-  var index = 0;
   for (var y = 0; y < height; y++) {
-    if (serpentine) direction = direction * -1;
+    if (serpentine) {
+      direction = direction * -1;
+    }
 
     final x0 = direction == 1 ? 0 : width - 1;
     final x1 = direction == 1 ? width : 0;
-    for (var x = x0; x != x1; x += direction, ++index, pIter.moveNext()) {
+    for (var x = x0; x != x1; x += direction, pIter.moveNext()) {
       // Get original color
       final pc = pIter.current;
       final r1 = pc[0].toInt();
       final g1 = pc[1].toInt();
       final b1 = pc[2].toInt();
 
       // Get converted color
-      var idx = quantizer.getColorIndexRgb(r1, g1, b1);
-      indexedImage.setPixelRgb(x, y, idx, 0, 0);
+      final idx = quantizer.getColorIndexRgb(r1, g1, b1);
+      indexedImage.setPixelIndex(x, y, idx);
 
       final r2 = palette.get(idx, 0);
       final g2 = palette.get(idx, 1);
@@ -118,13 +122,13 @@ Image ditherImage(Image image,
         final y1 = ds[i][2].toInt();
         if (x1 + x >= 0 && x1 + x < width && y1 + y >= 0 && y1 + y < height) {
           final d = ds[i][0];
-          idx = index + x1 + (y1 * width);
-          idx *= 4;
-          final p2 = image.getPixel(x1, y1);
+          final nx = x + x1;
+          final ny = y + y1;
+          final p2 = imageCopy.getPixel(nx, ny);
           p2
-            ..r = max(0, min(255, (p2.r + er * d).toInt()))
-            ..g = max(0, min(255, (p2.g + er * d).toInt()))
-            ..b = max(0, min(255, (p2.b + er * d).toInt()));
+            ..r = p2.r + er * d
+            ..g = p2.g + eg * d
+            ..b = p2.b + eb * d;
         }
       }
     }

diff --git a/test/_test_util.dart b/test/_test_util.dart
@@ -5,8 +5,8 @@ import 'package:archive/archive.dart';
 import 'package:image/image.dart';
 import 'package:test/test.dart';
 
-final testOutputPath = '${Directory.systemTemp.createTempSync().path}/out';
-//const testOutputPath = './_out';
+//final testOutputPath = '${Directory.systemTemp.createTempSync().path}/out';
+const testOutputPath = './_out';
 
 int hashImage(Image image) {
   var hash = 0;

diff --git a/test/filter/dither_image_test.dart b/test/filter/dither_image_test.dart
@@ -10,13 +10,13 @@ void main() {
       final bytes = File('test/_data/png/buck_24.png').readAsBytesSync();
       final i0 = decodePng(bytes)!;
 
-      var id = ditherImage(i0);
-      File('$testOutputPath/filter/dither_FloydSteinberg.png')
+      var id = ditherImage(i0, kernel: DitherKernel.atkinson);
+      File('$testOutputPath/filter/dither_Atkinson.png')
         ..createSync(recursive: true)
         ..writeAsBytesSync(encodePng(id));
 
-      id = ditherImage(i0, kernel: DitherKernel.atkinson);
-      File('$testOutputPath/filter/dither_Atkinson.png')
+      id = ditherImage(i0);
+      File('$testOutputPath/filter/dither_FloydSteinberg.png')
         ..createSync(recursive: true)
         ..writeAsBytesSync(encodePng(id));
 

diff --git a/test/filter/quantize_test.dart b/test/filter/quantize_test.dart
@@ -10,16 +10,28 @@ void main() {
       final bytes = File('test/_data/png/buck_24.png').readAsBytesSync();
 
       final i0 = decodePng(bytes)!;
-      quantize(i0, numberOfColors: 32, method: QuantizeMethod.octree);
+      final q0 = quantize(i0, numberOfColors: 32, method: QuantizeMethod.octree);
       File('$testOutputPath/filter/quantize_octree.png')
         ..createSync(recursive: true)
-        ..writeAsBytesSync(encodePng(i0));
+        ..writeAsBytesSync(encodePng(q0));
+
+      final i0_ = decodePng(bytes)!;
+      final q0_ = quantize(i0_, numberOfColors: 32, method: QuantizeMethod.octree, dither: DitherKernel.floydSteinberg);
+      File('$testOutputPath/filter/quantize_octree_dither.png')
+        ..createSync(recursive: true)
+        ..writeAsBytesSync(encodePng(q0_));
 
       final i1 = decodePng(bytes)!;
-      quantize(i1, numberOfColors: 32);
+      final q1 = quantize(i1, numberOfColors: 32);
       File('$testOutputPath/filter/quantize_neural.png')
         ..createSync(recursive: true)
-        ..writeAsBytesSync(encodePng(i1));
+        ..writeAsBytesSync(encodePng(q1));
+
+      final i2 = decodePng(bytes)!;
+      final q2 = quantize(i2, numberOfColors: 32, dither: DitherKernel.floydSteinberg);
+      File('$testOutputPath/filter/quantize_neural_dither.png')
+        ..createSync(recursive: true)
+        ..writeAsBytesSync(encodePng(q2));
     });
   });
 }