GNOME Bugzilla – Bug 727780
Colors -> Decompose discards exif data
Last modified: 2018-05-24 14:22:12 UTC
Decomposing an image to RGB channels as layers is a nice way to create a grayscale image. It's flexible to weightedly blend channels, and you get an instant preview. But when you save the image, all exif data is gone. It would be nice if the new image that gets created by using Colors -> Components -> Decompose inherits the exif data from the source image. $ gimp --verbose --version GNU Image Manipulation Program version 2.8.10 git-describe: GIMP_2_8_8-55-g9bb7eb0 using GEGL version 0.2.0 (compiled against version 0.2.0) using GLib version 2.38.2 (compiled against version 2.38.2) using GdkPixbuf version 2.30.6 (compiled against version 2.30.6) using GTK+ version 2.24.22 (compiled against version 2.24.22) using Pango version 1.36.3 (compiled against version 1.36.3) using Fontconfig version 2.11.0 (compiled against version 2.11.0) using Cairo version 1.12.16 (compiled against version 1.12.16)
1. Decomposing of an image creates a new image. The exif data are not valid any longer to a newly created image. So if you want to have the exif data of an other image attached to it, you have to make use of a metadata editor, where you can copy the metadata from one image to another. 2. Metadata handling is a new feature, new features will not be implemented in the gimp-2.8 branch anymore. Metadata handling is implemented in the gimp-2.9 development branch, leading to future gimp-2.10.
Intuitively, if an image gets decomposed, it was still shot with the same camera, at the same aperture, focal length, etc. So I would argue the exif data are still valid. Using an external metadata editor would be an additional, yet small, step in my already lengthy image postprocessing workflow, so I would prefer the tools in my toolchain to preserve metadata as far as possible. That being said, I understand that my use case might be a rare one, and if it's difficult to implement, no hard feelings. But let's say we want to make this a feature request for gimp-2.10, for its feasibility to be evaluated with regard to that version, how do we proceed? Can we transfer this ticket somehow? Should I open a new one?
The behavior of decompose is somewhat not completely specified and currently depends on the target color space. Two comments though: - Values are sometimes translated/scaled from the target color space bounds to fit in [0.0, 1.0]. So metadata will be hard to use as-is in such decomposed image. IIRC, some gamma correction are also sometimes applied too. - If the image is recomposed, then it makes sense to retrieve the original metadata in the re-composition.
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