raw input: fix LibRaw flip to Exif orientation conversion #3847
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lgritz
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May 19, 2023
lgritz
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May 19, 2023
fix formatting
lgritz
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AcademySoftwareFoundation:master
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May 20, 2023
…wareFoundation#3847) When reading a raw image while having a `user_flip` set to 1, we set the orientation Exif tag to LibRaw's flip value (so that LibRaw doesn't rotate and/or mirror the buffer but the image still gets displayed correctly). However LibRaw's convention for flip values differ from Exif orientation values: https://www.libraw.org/comment/5176#comment-5176. In this PR we fix this issue by converting LibRaw flip values to Exif orientation values. This conversion is based on: - https://www.libraw.org/comment/5178#comment-5178 (conversion proposed by LibRaw's maintainer) - https://github.com/LibRaw/LibRaw/blob/6fffd414bfda63dfef2276ae07f7ca36660b8888/src/write/file_write.cpp#L22 (LibRaw's function for applying the flip). Tested on: - CR2 images with flip values 1, 5 and 6 - ARW images with flip values 1 and 5 (unfortunately I could not find any image covering other flip values). Since the conversion is `[1, 2, 3, 4, 5, 6, 7, 8] -> [1, 2, 4, 3, 5, 8, 6, 7]`, the only test that came out with different results before and after the change is the one with flip value 6: in that case, the image orientation got corrected by the fix.
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May 31, 2023
When reading a raw image, setting the `user_flip` to 1 meant ignoring the `flip` value (to avoid buffer rotation from LibRaw). However the value 1 for the `user_flip` is **not neutral**: values lie between 0 and 7 (see https://www.libraw.org/docs/API-datastruct-eng.html#libraw_image_sizes_t), and 1 corresponds to a horizontal mirror (in my understanding of the source code). The proposed fix is to use 0 as `user_flip` value for ignoring the `flip` value. This modification invalidates the changes made in this PR: #3847. Therefore, flip to orientation conversion has been adapted to match exactly LibRaw's documentation, which handles only rotations (+90, +180, -90 degrees). The previous PR was only tested on images of landscape and human faces, hence the mirroring issue remained unnoticed. When reading images containing text however the problem is clearly visible. This PR fixes this mirroring issue on the following 4 orientations: 0, +90, +180 and -90 degrees rotation. Other orientations could not be tested as they don't seem to ever appear on raw images datasets.
lgritz
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Jun 1, 2023
When reading a raw image, setting the `user_flip` to 1 meant ignoring the `flip` value (to avoid buffer rotation from LibRaw). However the value 1 for the `user_flip` is **not neutral**: values lie between 0 and 7 (see https://www.libraw.org/docs/API-datastruct-eng.html#libraw_image_sizes_t), and 1 corresponds to a horizontal mirror (in my understanding of the source code). The proposed fix is to use 0 as `user_flip` value for ignoring the `flip` value. This modification invalidates the changes made in this PR: AcademySoftwareFoundation#3847. Therefore, flip to orientation conversion has been adapted to match exactly LibRaw's documentation, which handles only rotations (+90, +180, -90 degrees). The previous PR was only tested on images of landscape and human faces, hence the mirroring issue remained unnoticed. When reading images containing text however the problem is clearly visible. This PR fixes this mirroring issue on the following 4 orientations: 0, +90, +180 and -90 degrees rotation. Other orientations could not be tested as they don't seem to ever appear on raw images datasets.
birsoyo
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Jun 8, 2023
…wareFoundation#3847) When reading a raw image while having a `user_flip` set to 1, we set the orientation Exif tag to LibRaw's flip value (so that LibRaw doesn't rotate and/or mirror the buffer but the image still gets displayed correctly). However LibRaw's convention for flip values differ from Exif orientation values: https://www.libraw.org/comment/5176#comment-5176. In this PR we fix this issue by converting LibRaw flip values to Exif orientation values. This conversion is based on: - https://www.libraw.org/comment/5178#comment-5178 (conversion proposed by LibRaw's maintainer) - https://github.com/LibRaw/LibRaw/blob/6fffd414bfda63dfef2276ae07f7ca36660b8888/src/write/file_write.cpp#L22 (LibRaw's function for applying the flip). Tested on: - CR2 images with flip values 1, 5 and 6 - ARW images with flip values 1 and 5 (unfortunately I could not find any image covering other flip values). Since the conversion is `[1, 2, 3, 4, 5, 6, 7, 8] -> [1, 2, 4, 3, 5, 8, 6, 7]`, the only test that came out with different results before and after the change is the one with flip value 6: in that case, the image orientation got corrected by the fix.
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Description
When reading a raw image while having a
user_flipset to 1, we set the orientation Exif tag to LibRaw's flip value (so that LibRaw doesn't rotate and/or mirror the buffer but the image still gets displayed correctly).However LibRaw's convention for flip values differ from Exif orientation values: https://www.libraw.org/comment/5176#comment-5176.
In this PR we fix this issue by converting LibRaw flip values to Exif orientation values. This conversion is based on:
Tests
Tested on:
(unfortunately I could not find any image covering other flip values).
Since the conversion is
[1, 2, 3, 4, 5, 6, 7, 8] -> [1, 2, 4, 3, 5, 8, 6, 7], the only test that came out with different results before and after the change is the one with flip value 6:in that case, the image orientation got corrected by the fix.