Remove Exif orientation after saving it to irot/imir when reading JPEGs.

Currently we read the Exif Orientation tag and translate it to irot/imir,
but also leave the Exif as is.
However, MIAF says that AVIF files should not contain Exif transformations.

Fixes #3078.

Author: maryla-uc

CHANGELOG.md

@@ -27,6 +27,7 @@ The changes are relative to the previous release, unless the baseline is specifi
 * Add --sato flag to avifdec to enable Sample Transforms support at decoding.
 * Add --grid option to avifgainmaputil.
 * Apply clean aperture crop, rotation and mirror when decoding to PNG or JPEG.
+  Remove orientation information from Exif if present.
 
 ### Changed since 1.3.0
 
@@ -61,6 +62,8 @@ The changes are relative to the previous release, unless the baseline is specifi
   libaom v3.13.0 or later.
 * Converting an image containing a gain map using avifenc with the --grid flag
   now also splits the gain map into a grid.
+* In avifenc, set Exif orientation to 1 (no transformation) when converting
+  JPEGs to Avif.
 
 ### Removed since 1.3.0
 

apps/shared/avifjpeg.c

@@ -1394,15 +1394,22 @@ static avifBool avifJPEGReadInternal(FILE * f,
                     goto cleanup;
                 }
 
-                // Exif orientation, if any, is imported to avif->irot/imir and kept in avif->exif.
-                // libheif has the same behavior, see
-                // https://github.com/strukturag/libheif/blob/ea78603d8e47096606813d221725621306789ff2/examples/heif_enc.cc#L403
+                // Exif orientation, if any, is imported to avif->irot/imir, and the Exif data is saved to avif->exif.
                 if (avifImageSetMetadataExif(avif,
                                              marker->data + AVIF_JPEG_EXIF_HEADER_LENGTH,
                                              marker->data_length - AVIF_JPEG_EXIF_HEADER_LENGTH) != AVIF_RESULT_OK) {
                     fprintf(stderr, "Setting Exif metadata failed: %s (out of memory)\n", inputFilename);
                     goto cleanup;
                 }
+                // Set the Exif orientation to 1 (no transformation).
+                // ISO/IEC 23000-22:2024 (MIAF), Section 7.3.10.1:
+                //   There should be no image transformations expressed by Exif (rotation,
+                //   mirroring, etc.) indicated in the Exif metadata, in files encoded according
+                //   to this document.
+                // Do not check for errors, it's a "should" so ok to do on a best-effort basis.
+                // Moreover it should only fail if the Exif is marlformed or there is no orientation
+                // tag to begin with.
+                (void)avifSetExifOrientation(&avif->exif, 1);
                 found = AVIF_TRUE;
             }
         }

apps/shared/avifutil.c

@@ -622,7 +622,7 @@ avifBool avifImageSplitGrid(const avifImage * gridSplitImage, uint32_t gridCols,
         }
     }
     if (gridSplitImage->exif.size > 0) {
-        const avifResult result = avifImageSetMetadataExif(firstCell, gridSplitImage->exif.data, gridSplitImage->exif.size);
+        const avifResult result = avifRWDataSet(&firstCell->exif, gridSplitImage->exif.data, gridSplitImage->exif.size);
         if (result != AVIF_RESULT_OK) {
             fprintf(stderr, "ERROR: Failed to set Exif metadata on grid cell: %s\n", avifResultToString(result));
             return AVIF_FALSE;

tests/gtest/avifmetadatatest.cc

@@ -246,11 +246,21 @@ TEST(MetadataTest, ExifOrientation) {
       testutil::ReadImage(data_path, "paris_exif_orientation_5.jpg");
   ASSERT_NE(image, nullptr);
   // The Exif metadata contains orientation information: 5.
+  // When reading the JPEG file, the Exif orientation is set to 1.
   EXPECT_GT(image->exif.size, 0u);
   EXPECT_EQ(image->transformFlags & (AVIF_TRANSFORM_IROT | AVIF_TRANSFORM_IMIR),
             avifTransformFlags{AVIF_TRANSFORM_IROT | AVIF_TRANSFORM_IMIR});
   EXPECT_EQ(image->irot.angle, 1u);
   EXPECT_EQ(image->imir.axis, 0u);
+  testutil::AvifRwData originalReadExif;
+  ASSERT_EQ(
+      avifRWDataSet(&originalReadExif, image->exif.data, image->exif.size),
+      AVIF_RESULT_OK);
+  // For testing purposes, set back the orientation.
+  ASSERT_EQ(avifSetExifOrientation(&image->exif, 5), AVIF_RESULT_OK);
+  // The two Exifs are different, showing that the Orientation was indeed
+  // modified when reading.
+  EXPECT_FALSE(testutil::AreByteSequencesEqual(originalReadExif, image->exif));
 
   const testutil::AvifRwData encoded =
       testutil::Encode(image.get(), AVIF_SPEED_FASTEST);
@@ -313,6 +323,15 @@ TEST(MetadataTest, ExifOrientationAndForcedImir) {
   EXPECT_GT(image->exif.size, 0u);
   image->transformFlags = AVIF_TRANSFORM_IMIR;
   image->imir.axis = 1;
+  testutil::AvifRwData originalReadExif;
+  ASSERT_EQ(
+      avifRWDataSet(&originalReadExif, image->exif.data, image->exif.size),
+      AVIF_RESULT_OK);
+  // For testing purposes, set back the orientation.
+  ASSERT_EQ(avifSetExifOrientation(&image->exif, 5), AVIF_RESULT_OK);
+  // The two Exifs are different, showing that the Orientation was indeed
+  // modified when reading.
+  EXPECT_FALSE(testutil::AreByteSequencesEqual(originalReadExif, image->exif));
 
   const testutil::AvifRwData encoded =
       testutil::Encode(image.get(), AVIF_SPEED_FASTEST);