Add BinaryQuantizer

lib/image.dart

@@ -227,6 +227,7 @@ export 'src/transform/copy_resize_crop_square.dart';
 export 'src/transform/copy_rotate.dart';
 export 'src/transform/flip.dart';
 export 'src/transform/trim.dart';
+export 'src/util/binary_quantizer.dart';
 export 'src/util/clip_line.dart';
 export 'src/util/color_util.dart';
 export 'src/util/file_access.dart';
@@ -238,4 +239,5 @@ export 'src/util/neural_quantizer.dart';
 export 'src/util/octree_quantizer.dart';
 export 'src/util/output_buffer.dart';
 export 'src/util/point.dart';
+export 'src/util/quantizer.dart';
 export 'src/util/random.dart';

lib/src/filter/dither_image.dart

@@ -116,7 +116,9 @@ Image ditherImage(Image image,
       for (var i = i0; i != i1; i += direction) {
         final x1 = ds[i][1].toInt();
         final y1 = ds[i][2].toInt();
-        if ((x1 + x) >= 0 && (x1 + x) < width && (y1 + y) >= 0 &&
+        if ((x1 + x) >= 0 &&
+            (x1 + x) < width &&
+            (y1 + y) >= 0 &&
             (y1 + y) < height) {
           final d = ds[i][0];
           final nx = x + x1;

lib/src/filter/quantize.dart

@@ -1,10 +1,11 @@
 import '../image/image.dart';
+import '../util/binary_quantizer.dart';
 import '../util/neural_quantizer.dart';
 import '../util/octree_quantizer.dart';
 import '../util/quantizer.dart';
 import 'dither_image.dart';
 
-enum QuantizeMethod { neuralNet, octree }
+enum QuantizeMethod { neuralNet, octree, binary }
 
 /// Quantize the number of colors in image to 256.
 Image quantize(Image src,
@@ -16,8 +17,10 @@ Image quantize(Image src,
 
   if (method == QuantizeMethod.octree || numberOfColors < 4) {
     quantizer = OctreeQuantizer(src, numberOfColors: numberOfColors);
-  } else {
+  } else if (method == QuantizeMethod.octree) {
     quantizer = NeuralQuantizer(src, numberOfColors: numberOfColors);
+  } else {
+    quantizer = BinaryQuantizer();
   }
 
   return ditherImage(src,

lib/src/formats/gif_encoder.dart

@@ -2,6 +2,7 @@ import 'dart:typed_data';
 
 import '../filter/dither_image.dart';
 import '../image/image.dart';
+import '../util/binary_quantizer.dart';
 import '../util/image_exception.dart';
 import '../util/neural_quantizer.dart';
 import '../util/octree_quantizer.dart';
@@ -39,8 +40,10 @@ class GifEncoder extends Encoder {
         if (quantizerType == QuantizerType.neural) {
           _lastColorMap = NeuralQuantizer(image,
               numberOfColors: numColors, samplingFactor: samplingFactor);
-        } else {
+        } else if (quantizerType == QuantizerType.octree) {
           _lastColorMap = OctreeQuantizer(image, numberOfColors: numColors);
+        } else if (quantizerType == QuantizerType.binary) {
+          _lastColorMap = BinaryQuantizer();
         }
 
         _lastImage = ditherImage(image,
@@ -71,8 +74,10 @@ class GifEncoder extends Encoder {
       if (quantizerType == QuantizerType.neural) {
         _lastColorMap = NeuralQuantizer(image,
             numberOfColors: numColors, samplingFactor: samplingFactor);
-      } else {
+      } else if (quantizerType == QuantizerType.octree) {
         _lastColorMap = OctreeQuantizer(image, numberOfColors: numColors);
+      } else if (quantizerType == QuantizerType.binary) {
+        _lastColorMap = BinaryQuantizer();
       }
 
       _lastImage = ditherImage(image,

lib/src/util/binary_quantizer.dart

@@ -0,0 +1,31 @@
+import '../color/color.dart';
+import '../color/color_uint8.dart';
+import '../image/palette.dart';
+import '../image/palette_uint8.dart';
+import '../util/color_util.dart';
+import 'quantizer.dart';
+
+class BinaryQuantizer extends Quantizer {
+  final Palette _palette;
+
+  BinaryQuantizer() : _palette = PaletteUint8(2, 3) {
+    _palette.setRgb(1, 255, 255, 255);
+  }
+
+  @override
+  Palette get palette => _palette;
+
+  @override
+  Color getQuantizedColor(Color c) => c.luminanceNormalized < 0.5
+      ? ColorRgb8(_palette.getRed(0) as int, _palette.getGreen(0) as int,
+          _palette.getBlue(0) as int)
+      : ColorRgb8(_palette.getRed(1) as int, _palette.getGreen(1) as int,
+          _palette.getBlue(1) as int);
+
+  @override
+  int getColorIndex(Color c) => c.luminanceNormalized < 0.5 ? 0 : 1;
+
+  @override
+  int getColorIndexRgb(int r, int g, int b) =>
+      getLuminanceRgb(r, g, b) < 0.5 ? 0 : 1;
+}

lib/src/util/quantizer.dart

@@ -2,7 +2,7 @@ import '../color/color.dart';
 import '../image/image.dart';
 import '../image/palette.dart';
 
-enum QuantizerType { octree, neural }
+enum QuantizerType { octree, neural, binary }
 
 /// Abstract class for color quantizers, which reduce the total number of colors
 /// used by an image to a given maximum, used to convert images to palette

test/filter/quantize_test.dart

@@ -32,12 +32,18 @@ void main() {
         ..writeAsBytesSync(encodePng(q1));
 
       final i2 = decodePng(bytes)!;
-      final q2 =
-          quantize(grayscale(i2), numberOfColors: 2,
-              dither: DitherKernel.floydSteinberg);
+      final q2 = quantize(grayscale(i2),
+          numberOfColors: 2, dither: DitherKernel.floydSteinberg);
       File('$testOutputPath/filter/quantize_neural_dither.png')
         ..createSync(recursive: true)
         ..writeAsBytesSync(encodePng(q2));
+
+      final i3 = decodePng(File('test/_data/png/david.png').readAsBytesSync())!;
+      final q3 = quantize(i3,
+          method: QuantizeMethod.binary, dither: DitherKernel.floydSteinberg);
+      File('$testOutputPath/filter/quantize_binary.png')
+        ..createSync(recursive: true)
+        ..writeAsBytesSync(encodePng(q3));
     });
   });
 }