DICOM: Add support for nested sequences #2558
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A sequence is like a folder, so attribute changes within the sequence/folder should only apply to images contained within. The previous attributes must be restored once the sequence ends and processing returns to the parent "folder". Fixes #2534.
urban-warrior
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Sep 13, 2020
netbsd-srcmastr
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2020-09-19 7.0.10-30 <quetzlzacatenango@image...>
* Release ImageMagick version 7.0.10-30 GIT revision 17641:ab95f7264:20200919
2020-09-07 7.0.10-30 <quetzlzacatenango@image...>
* Add endian support to JSON coder.
* Regression: MapCache type cache allocation skipped (reference
ImageMagick/ImageMagick6#97).
* Some DCM images include a thumbnail (reference
ImageMagick/ImageMagick#2558).
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Prerequisites
Description
This fixes #2534.
The DICOM code was not handling sequences, which are like folders. Inside a sequence/folder, attributes like the image dimensions can be changed, but these only apply to images within the sequence/folder. Once exiting the sequence and returning to the parent "folder", the previous image attributes must be restored.
Issue #2534 has a sample image file that initially sets the image dimensions to 2101x2101, however it then begins a sequence for a thumbnail, which sets the dimensions to 64x64 and has some pixel data. After exiting that sequence, the original image dimensions are meant to be restored, however this was not happening. As a result the main image was read as 64x64 and the unused pixel data was then treated as further DICOM header information for a subsequent image, causing unrelated errors.
This PR uses ImageMagick's linked list implementation to push the relevant image attributes onto a stack each time a sequence is encountered, so that when the sequence is exited, the original attributes are restored. It fixes the issue and allows the sample image to be read correctly (both the thumbnail and the main image).