raw input: fix user_flip usage #3858
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lgritz
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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.
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Description
When reading a raw image, setting the
user_flipto 1 meant ignoring theflipvalue (to avoid buffer rotation from LibRaw).However the value 1 for the
user_flipis 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_flipvalue for ignoring theflipvalue.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).
Tests
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.