Add LJpeg predictors 2-7

darktable-org · Dec 30, 2021 · 8e0c81d · 8e0c81d
1 parent a571881
commit 8e0c81d
Showing 1 changed file with 66 additions and 5 deletions.
diff --git a/src/librawspeed/decompressors/LJpegDecompressor.cpp b/src/librawspeed/decompressors/LJpegDecompressor.cpp
@@ -91,7 +91,7 @@ void LJpegDecompressor::decodeScan()
 {
   assert(frame.cps > 0);
 
-  if (predictorMode != 1)
+  if ((predictorMode < 1) || (predictorMode > 7))
     ThrowRDE("Unsupported predictor mode: %u", predictorMode);
 
   for (uint32_t i = 0; i < frame.cps; i++)
@@ -194,15 +194,47 @@ template <int N_COMP, bool WeirdWidth> void LJpegDecompressor::decodeN() {
     copy_n(predNext, N_COMP, pred.data());
     // the predictor for the next line is the start of this line
     predNext = &img(row, col);
+    // the predictor mode is always horizontal on the first line
+    uint32_t predMode = row == 0 ? 1 : predictorMode;
 
     // FIXME: predictor may have value outside of the uint16_t.
     // https://github.com/darktable-org/rawspeed/issues/175
 
     // For x, we first process all full pixel blocks within the image buffer ...
     for (; col < N_COMP * fullBlocks; col += N_COMP) {
       for (int i = 0; i != N_COMP; ++i) {
-        pred[i] = uint16_t(pred[i] + ht[i]->decodeDifference(bitStream));
-        img(row, col + i) = pred[i];
+        img(row, col + i) =
+            uint16_t(pred[i] + ht[i]->decodeDifference(bitStream));
+        if (col < N_COMP * (fullBlocks - 1)) {
+          int predA = img(row, col + i);
+          int predB = predMode > 1 ? img(row - 1, col + N_COMP + i) : 0;
+          int predC = predMode > 1 ? img(row - 1, col + i) : 0;
+          switch (predMode) {
+          case 1:
+            pred[i] = uint16_t(predA);
+            break;
+          case 2:
+            pred[i] = uint16_t(predB);
+            break;
+          case 3:
+            pred[i] = uint16_t(predC);
+            break;
+          case 4:
+            pred[i] = uint16_t(predA + predB - predC);
+            break;
+          case 5:
+            pred[i] = uint16_t(predA + ((predB - predC) >> 1));
+            break;
+          case 6:
+            pred[i] = uint16_t(predB + ((predA - predC) >> 1));
+            break;
+          case 7:
+            pred[i] = uint16_t((predA + predB) >> 1);
+            break;
+          default:
+            ThrowRDE("Unsupported predictor mode: %u", predMode);
+          }
+        }
       }
     }
 
@@ -217,8 +249,37 @@ template <int N_COMP, bool WeirdWidth> void LJpegDecompressor::decodeN() {
       assert(trailingPixels < N_COMP);
       unsigned c = 0;
       for (; c < trailingPixels; ++c) {
-        pred[c] = uint16_t(pred[c] + ht[c]->decodeDifference(bitStream));
-        img(row, col + c) = pred[c];
+        // Continue predictor update skipped at last full block
+        int predA = img(row, col - N_COMP + c);
+        int predB = predMode > 1 ? img(row - 1, col + c) : 0;
+        int predC = predMode > 1 ? img(row - 1, col - N_COMP + c) : 0;
+        switch (predMode) {
+        case 1:
+          pred[c] = uint16_t(predA);
+          break;
+        case 2:
+          pred[c] = uint16_t(predB);
+          break;
+        case 3:
+          pred[c] = uint16_t(predC);
+          break;
+        case 4:
+          pred[c] = uint16_t(predA + predB - predC);
+          break;
+        case 5:
+          pred[c] = uint16_t(predA + ((predB - predC) >> 1));
+          break;
+        case 6:
+          pred[c] = uint16_t(predB + ((predA - predC) >> 1));
+          break;
+        case 7:
+          pred[c] = uint16_t((predA + predB) >> 1);
+          break;
+        default:
+          ThrowRDE("Unsupported predictor mode: %u", predMode);
+        }
+        img(row, col + c) =
+            uint16_t(pred[c] + ht[c]->decodeDifference(bitStream));
       }
       // Discard the rest of the block.
       assert(c < N_COMP);