Changes the DNG preview/thumbnail handling.
A thumbnail is at max 256x256 pixel large. A preview has to be larger than a thumbnail.
diff --git a/src/piex.cc b/src/piex.cc
index 09b154a..6de2b4d 100644
--- a/src/piex.cc
+++ b/src/piex.cc
@@ -121,8 +121,26 @@
stream, exif_ifd, &next_ifd_offset);
}
-bool GetImageFromIfd(const TiffDirectory& ifd, std::uint32_t* offset,
- std::uint32_t* length) {
+struct Image {
+ std::uint16_t width = 0;
+ std::uint16_t height = 0;
+ std::uint32_t length = 0;
+ std::uint32_t offset = 0;
+
+ bool operator>(const Image& rhs) const {
+ return width > rhs.width && height > rhs.height;
+ }
+};
+
+bool IsThumbnail(const Image& image) {
+ // According to Tiff/EP a thumbnail has max 256 pixels per dimension.
+ // http://standardsproposals.bsigroup.com/Home/getPDF/567
+ const std::uint16_t kThumbnailAxis = 256;
+ return image.width <= kThumbnailAxis && image.height <= kThumbnailAxis;
+}
+
+bool GetImageFromIfd(const TiffDirectory& ifd, StreamInterface* stream,
+ Image* image) {
std::uint32_t compression;
std::uint32_t photometric_interpretation;
if (ifd.Get(kTiffTagPhotometric, &photometric_interpretation) &&
@@ -134,9 +152,10 @@
if (ifd.Get(kTiffTagStripOffsets, &strip_offsets) &&
ifd.Get(kTiffTagStripByteCounts, &byte_counts) &&
strip_offsets.size() == 1 && byte_counts.size() == 1) {
- *length = byte_counts[0];
- *offset = strip_offsets[0];
- return true;
+ image->length = byte_counts[0];
+ image->offset = strip_offsets[0];
+ return GetPreviewDimensions(image->offset, stream, &image->width,
+ &image->height);
}
}
}
@@ -395,41 +414,41 @@
return error;
}
- // Find the largest and smallest jpeg compressed preview image.
- std::uint32_t preview_length = 0;
- std::uint32_t preview_offset = 0;
- std::uint32_t thumbnail_length = std::numeric_limits<std::uint32_t>::max();
- std::uint32_t thumbnail_offset = std::numeric_limits<std::uint32_t>::max();
+ // Find the jpeg compressed thumbnail and preview image.
+ Image preview;
+ Image thumbnail;
- std::uint32_t length = 0;
- std::uint32_t offset = 0;
- if (GetImageFromIfd(tiff_content.tiff_directory[0], &offset, &length)) {
- preview_length = length;
- preview_offset = offset;
- thumbnail_length = length;
- thumbnail_offset = offset;
+ // Search for images in IFD0
+ Image temp_image;
+ if (GetImageFromIfd(tiff_content.tiff_directory[0], stream, &temp_image)) {
+ if (IsThumbnail(temp_image)) {
+ thumbnail = temp_image;
+ } else {
+ preview = temp_image;
+ }
}
+ // Search for images in other IFDs
for (const auto& ifd : tiff_content.tiff_directory[0].GetSubDirectories()) {
- if (GetImageFromIfd(ifd, &offset, &length)) {
- if (length > preview_length) {
- preview_length = length;
- preview_offset = offset;
- }
- if (length < thumbnail_length) {
- thumbnail_length = length;
- thumbnail_offset = offset;
+ if (GetImageFromIfd(ifd, stream, &temp_image)) {
+ // Try to find the largest thumbnail/preview.
+ if (IsThumbnail(temp_image)) {
+ if (temp_image > thumbnail) {
+ thumbnail = temp_image;
+ }
+ } else {
+ if (temp_image > preview) {
+ preview = temp_image;
+ }
}
}
}
- preview_image_data->preview_length = preview_length;
- preview_image_data->preview_offset = preview_offset;
- // A thumbnail image is supposed to be smaller compared to the preview.
- if (thumbnail_length < preview_length) {
- preview_image_data->thumbnail_length = thumbnail_length;
- preview_image_data->thumbnail_offset = thumbnail_offset;
- }
+ preview_image_data->preview_length = preview.length;
+ preview_image_data->preview_offset = preview.offset;
+ preview_image_data->thumbnail_length = thumbnail.length;
+ preview_image_data->thumbnail_offset = thumbnail.offset;
+
return kOk;
}