diff --git a/lib/Dither.dart b/lib/Dither.dart
index 8579376..7f1cdb9 100644
--- a/lib/Dither.dart
+++ b/lib/Dither.dart
@@ -14,7 +14,33 @@ class Pixed {
         px.b = average;
       }
     }
+    return pxArr;
+  }
 
+  static PixelArray quantize(PixelArray image, [int steps=1]) {
+    PixelArray pxArr = new PixelArray.fromPixelArray(image);
+    for (var y = 0; y < pxArr.getHeight(); y++) {
+      for (var x = 0; x < pxArr.getWidth(); x++) {
+        var px = pxArr.getPixel(x, y);
+        px.r = (steps * px.r / 255).round() * (255 ~/ steps);
+        px.g = (steps * px.g / 255).round() * (255 ~/ steps);
+        px.b = (steps * px.b / 255).round() * (255 ~/ steps);
+      }
+    }
+    return pxArr;
+  }
+
+  static PixelArray calcQuantizeError(PixelArray original, PixelArray quantized) {
+    PixelArray pxArr = new PixelArray.fromPixelArray(original);
+    for (var y = 0; y < pxArr.getHeight(); y++) {
+      for (var x = 0; x < pxArr.getWidth(); x++) {
+        Pixel px = pxArr.getPixel(x, y);
+        Pixel quant = quantized.getPixel(x, y);
+        px.r = px.r - quant.r;
+        px.g = px.g - quant.g;
+        px.b = px.b - quant.b;
+      }
+    }
     return pxArr;
   }
 }