Lightroom Previews

[piepmatz]

Modifications done with Lightroom are not directly applied to the images, instead the operations are saved and only applied when exporting the modified image.
When using Lightroom as wallpaper source, we can only extract the path to the master file, so the wallpaper is just the image without any modifications made in Lightroom.
I don't know a way to trigger exporting the chosen image from command line, but another approach might be worth looking into:
Lightroom saves previews of its images, and different quality settings for those previous can be chosen. If there is a 1080p preview available for all images, we might try taking that as the source for the wallpaper instead of the image's master file.

[piepmatz]

Well, it is possible.
However, previews in standard size are 1440x960, a bit too small. The next option would be a full-size preview. Those would require a lot of disk space, so it would be better to just export the Lightroom images in 1080p somewhere and use that directory as image source.

Just in case I will consider extracting images from previews again, here are some helpful links:

• https://helpx.adobe.com/lightroom/kb/extract-previews-for-lost-images-lightroom.html (Adobe's official plugin, compiled Lua file, decompilation was not really helpful)
• https://github.com/arron-h/enlighten-desktop/blob/24c9e5214e323c1df4d2cf6444c5146fa5ff79b7/src/lrprev.cpp
• https://github.com/arnar/lightroommate/blob/master/lrprev.py
• https://github.com/jarnoh/quicklook-lightroom/blob/master/quicklook-lightroom/LrPrevImageData.m
• https://github.com/Chandler/lightroom_preview_exporter/blob/master/extract_image.py
• https://github.com/timh/lightroom-rails/blob/master/PreviewParser.rb
• https://github.com/karelia/iMedia/blob/2c3305aac9bc5577c8149fa05e7e1942363e3492/IMBLightroom3or4Parser.m
• https://github.com/nagyist/assembla-ltrplugins/blob/6cf9899f538095656d7c893847b17892bd52f66f/trunk/Framework/Catalog/Previews.lua

The extracted image seems to not have the correct color profile. This can be changed using Pillow:

• python-pillow/Pillow#1662
• https://stackoverflow.com/questions/13672777/python-pil-changing-colour-profile-to-untagged-rgb-on-crop-scale-and-save
• https://hipolabs.com/en/blog/icc-profile-transformation-using-pil/
• https://pillow.readthedocs.io/en/3.4.x/reference/ImageCms.html