Encoder: fix ispe property for tmap with grid. (#2730)

Decoder: check the ispe property of tmap items.

The new check will fail files with gain map grids created with previous versions of libavif. However, I believe that there are probably zero such images (apart from test images in this repo). avifenc cannot produce such images: if you specify --grid it discards the gain map (this is a bug, not intentional). So you would have to write specific code to call the API to produce such images.

Author: maryla-uc

src/read.c

@@ -5704,6 +5704,19 @@ static avifResult avifDecoderFindGainMapItem(const avifDecoder * decoder,
         gainMap->altDepth = pixiProp->u.pixi.planeDepths[0];
     }
 
+    const avifProperty * ispeProp = avifPropertyArrayFind(&toneMappedImageItemTmp->properties, "ispe");
+    if (!ispeProp) {
+        // HEIF (ISO/IEC 23008-12:2022), Section 6.5.3.1:
+        // Every image item shall be associated with one property of this type, prior to the association
+        // of all transformative properties.
+        avifDiagnosticsPrintf(data->diag, "Box[tmap] missing mandatory ispe property");
+        return AVIF_RESULT_BMFF_PARSE_FAILED;
+    }
+    if (ispeProp->u.ispe.width != colorItem->width || ispeProp->u.ispe.height != colorItem->height) {
+        avifDiagnosticsPrintf(data->diag, "Box[tmap] ispe property width/height does not match base image");
+        return AVIF_RESULT_BMFF_PARSE_FAILED;
+    }
+
     if (avifPropertyArrayFind(&toneMappedImageItemTmp->properties, "pasp") ||
         avifPropertyArrayFind(&toneMappedImageItemTmp->properties, "clap") ||
         avifPropertyArrayFind(&toneMappedImageItemTmp->properties, "irot") ||

src/write.c

@@ -1046,10 +1046,12 @@ size_t avifEncoderGetGainMapSizeBytes(avifEncoder * encoder)
 }
 
 // Sets altImageMetadata's metadata values to represent the "alternate" image as if applying the gain map to the base image.
-static avifResult avifImageCopyAltImageMetadata(avifImage * altImageMetadata, const avifImage * imageWithGainMap)
+// For grid images, imageWithGainMap is the metadata of the first cell. gridWidth and gridHeight are the dimensions of the
+// full image.
+static avifResult avifImageCopyAltImageMetadata(avifImage * altImageMetadata, const avifImage * imageWithGainMap, uint32_t gridWidth, uint32_t gridHeight)
 {
-    altImageMetadata->width = imageWithGainMap->width;
-    altImageMetadata->height = imageWithGainMap->height;
+    altImageMetadata->width = gridWidth;
+    altImageMetadata->height = gridHeight;
     AVIF_CHECKRES(avifRWDataSet(&altImageMetadata->icc, imageWithGainMap->gainMap->altICC.data, imageWithGainMap->gainMap->altICC.size));
     altImageMetadata->colorPrimaries = imageWithGainMap->gainMap->altColorPrimaries;
     altImageMetadata->transferCharacteristics = imageWithGainMap->gainMap->altTransferCharacteristics;
@@ -1885,14 +1887,17 @@ static avifResult avifEncoderAddImageInternal(avifEncoder * encoder,
     if (encoder->data->items.count == 0) {
         // Make a copy of the first image's metadata (sans pixels) for future writing/validation
         AVIF_CHECKRES(avifImageCopy(encoder->data->imageMetadata, firstCell, 0));
+
+        const uint32_t gridWidth = avifGridWidth(gridCols, firstCell, bottomRightCell);
+        const uint32_t gridHeight = avifGridHeight(gridRows, firstCell, bottomRightCell);
+
         if (hasGainMap) {
-            AVIF_CHECKRES(avifImageCopyAltImageMetadata(encoder->data->altImageMetadata, encoder->data->imageMetadata));
+            AVIF_CHECKRES(
+                avifImageCopyAltImageMetadata(encoder->data->altImageMetadata, encoder->data->imageMetadata, gridWidth, gridHeight));
         }
 
         // Prepare all AV1 items
         uint16_t colorItemID;
-        const uint32_t gridWidth = avifGridWidth(gridCols, firstCell, bottomRightCell);
-        const uint32_t gridHeight = avifGridHeight(gridRows, firstCell, bottomRightCell);
         AVIF_CHECKRES(avifEncoderAddImageItems(encoder, gridCols, gridRows, gridWidth, gridHeight, AVIF_ITEM_COLOR, &colorItemID));
         encoder->data->primaryItemID = colorItemID;