jpeg decoder cleanup

undoanu · May 1, 2015 · 41c211b · 41c211b
1 parent 7624339
commit 41c211b
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Showing 5 changed files with 28 additions and 21 deletions.
diff --git a/lib/src/formats/jpeg/jpeg.dart b/lib/src/formats/jpeg/jpeg.dart
@@ -2,16 +2,6 @@ part of image;
 
 class Jpeg {
   static const List<int> dctZigZag = const [
-      0,  1,  5,  6, 14, 15, 27, 28,
-      2,  4,  7, 13, 16, 26, 29, 42,
-      3,  8, 12, 17, 25, 30, 41, 43,
-      9, 11, 18, 24, 31, 40, 44, 53,
-      10, 19, 23, 32, 39, 45, 52, 54,
-      20, 22, 33, 38, 46, 51, 55, 60,
-      21, 34, 37, 47, 50, 56, 59, 61,
-      35, 36, 48, 49, 57, 58, 62, 63 ];
-
-  static const List<int> dctNaturalOrder = const [
       0,  1,  8, 16,  9,  2,  3, 10,
       17, 24, 32, 25, 18, 11,  4,  5,
       12, 19, 26, 33, 40, 48, 41, 34,

diff --git a/lib/src/formats/jpeg/jpeg_component.dart b/lib/src/formats/jpeg/jpeg_component.dart
@@ -3,7 +3,7 @@ part of image;
 class JpegComponent {
   int h;
   int v;
-  final List<Int32List> quantizationTableList;
+  final List<Int16List> quantizationTableList;
   int quantizationIndex;
   int blocksPerLine;
   int blocksPerColumn;
@@ -15,6 +15,6 @@ class JpegComponent {
   JpegComponent(this.h, this.v, this.quantizationTableList,
       this.quantizationIndex);
 
-  Int32List get quantizationTable =>
+  Int16List get quantizationTable =>
       quantizationTableList[quantizationIndex];
 }
diff --git a/lib/src/formats/jpeg/jpeg_data.dart b/lib/src/formats/jpeg/jpeg_data.dart
@@ -442,10 +442,10 @@ class JpegData  {
       }
 
       if (quantizationTables[n] == null) {
-        quantizationTables[n] = new Int32List(64);;
+        quantizationTables[n] = new Int16List(64);
       }
 
-      Int32List tableData = quantizationTables[n];
+      Int16List tableData = quantizationTables[n];
       for (int i = 0; i < Jpeg.DCTSIZE2; i++) {
         int tmp;
         if (prec != 0) {
@@ -454,7 +454,7 @@ class JpegData  {
           tmp = block.readByte();
         }
 
-        tableData[Jpeg.dctNaturalOrder[i]] = tmp;
+        tableData[Jpeg.dctZigZag[i]] = tmp;
       }
     }
 
@@ -661,14 +661,24 @@ class JpegData  {
     return lines;
   }
 
+  static int toFix(double val) {
+    const int FIXED_POINT = 20;
+    const int ONE = 1 << FIXED_POINT;
+
+    return (val * ONE).toInt() & 0xffffffff;
+  }
+
   static Uint8List dctClip;
   /**
    * A port of poppler's IDCT method which in turn is taken from:
    * Christoph Loeffler, Adriaan Ligtenberg, George S. Moschytz,
    * "Practical Fast 1-D DCT Algorithms with 11 Multiplications",
    * IEEE Intl. Conf. on Acoustics, Speech & Signal Processing, 1989, 988-991.
+   *
+   * TODO I'm pretty sure the rounding errors in some pixels are coming from
+   * here.
    */
-  void _quantizeAndInverse(Int32List quantizationTable,
+  void _quantizeAndInverse(Int16List quantizationTable,
                            Int32List coefBlock,
                            Uint8List dataOut,
                            Int32List dataIn) {

diff --git a/lib/src/formats/jpeg/jpeg_scan.dart b/lib/src/formats/jpeg/jpeg_scan.dart
@@ -166,20 +166,26 @@ class JpegScan {
     int diff = t == 0 ? 0 : _receiveAndExtend(t);
     component.pred += diff;
     zz[0] = component.pred;
+
     int k = 1;
     while (k < 64) {
       var rs = _decodeHuffman(component.huffmanTableAC);
       int s = rs & 15;
       int r = rs >> 4;
       if (s == 0) {
-        if (r < 15)
+        if (r < 15) {
           break;
+        }
         k += 16;
         continue;
       }
+
       k += r;
-      int z = Jpeg.dctNaturalOrder[k];
-      zz[z] = _receiveAndExtend(s);
+
+      s = _receiveAndExtend(s);
+
+      int z = Jpeg.dctZigZag[k];
+      zz[z] = s;
       k++;
     }
   }
@@ -215,7 +221,7 @@ class JpegScan {
         continue;
       }
       k += r;
-      int z = Jpeg.dctNaturalOrder[k];
+      int z = Jpeg.dctZigZag[k];
       zz[z] = (_receiveAndExtend(s) * (1 << successive));
       k++;
     }
@@ -226,7 +232,7 @@ class JpegScan {
     int e = spectralEnd;
     int r = 0;
     while (k <= e) {
-      int z = Jpeg.dctNaturalOrder[k];
+      int z = Jpeg.dctZigZag[k];
       switch (successiveACState) {
         case 0: // initial state
           int rs = _decodeHuffman(component.huffmanTableAC);

diff --git a/test/jpeg_test.dart b/test/jpeg_test.dart
@@ -43,6 +43,7 @@ void defineJpegTests() {
       expect(image.width, equals(227));
       expect(image.height, equals(149));
 
+      // This test identifies the rounding error in some pixels.
       /*for (int y = 0; y < image.height; ++y) {
         for (int x = 0; x < image.width; ++x) {
           expect(image.getPixel(x, y), equals(png.getPixel(x, y)),