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Changes the DNG preview/thumbnail handling.

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A thumbnail is at max 256x256 pixel large. A preview has to be larger than a thumbnail.

Bug: 27097813
This commit is contained in:
Eik Brauer
2016-02-17 14:05:49 +01:00
committed by Yujie Qin
parent e706483e58
commit 30570695ab
1 changed files with 51 additions and 32 deletions
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83
src/piex.cc
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@@ -121,8 +121,26 @@ Error GetExifIfd(const Endian endian, StreamInterface* stream,
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 @@ bool GetImageFromIfd(const TiffDirectory& ifd, std::uint32_t* offset,
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 @@ Error DngGetPreviewData(StreamInterface* stream,
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;
}