Colors: Add libvips support to preserve ICC profiles in thumbnails

[bobobo1618]

As a user who has pictures with color profiles other than sRGB, I want PhotoPrism to preserve them in the generated thumbnails so that the colors are properly reproduced on devices/displays that support ICC profiles.

Since thumbnail generation with libvips seems mature enough and we haven't noticed any particular issues or downsides, we've decided to make it the default in our upcoming release without waiting any further. We have updated our preview build so that you can test the latest changes and improvements:

• https://docs.photoprism.app/release-notes/#development-preview
• https://docs.photoprism.app/getting-started/updates/#development-preview

The following config options will be available with our upcoming release (or when using the preview build):

Environment	CLI Flag	Default	Description
PHOTOPRISM_THUMB_LIBRARY	--thumb-library	auto	image processing LIBRARY to be used for generating thumbnails (auto, imaging, vips)
PHOTOPRISM_THUMB_COLOR	--thumb-color	auto	standard color PROFILE for thumbnails (auto, preserve, srgb, none)
PHOTOPRISM_THUMB_FILTER	--thumb-filter	auto	downscaling filter NAME (imaging best to worst: blackman, lanczos, cubic, linear, nearest)
PHOTOPRISM_THUMB_SIZE	--thumb-size	1920	maximum size of pre-generated thumbnails in PIXELS (720-7680)
PHOTOPRISM_THUMB_SIZE_UNCACHED	--thumb-size-uncached	7680	maximum size of thumbnails generated on demand in PIXELS (720-7680)
PHOTOPRISM_THUMB_UNCACHED	--thumb-uncached		generate missing thumbnails on demand (high memory and cpu usage)
PHOTOPRISM_JPEG_QUALITY	--jpeg-quality	83	higher values increase the image QUALITY and file size (25-100)
PHOTOPRISM_JPEG_SIZE	--jpeg-size	7680	maximum size of generated JPEG images in PIXELS (720-30000)
PHOTOPRISM_PNG_SIZE	--png-size	7680	maximum size of generated PNG images in PIXELS (720-30000)

If you build from source or use one of our binary installation packages, please note that the system on which you build and/or run PhotoPrism must have libvips >= 8.10 installed.

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Original Issue Report

Steps to reproduce:

• Obtain image with an ICC profile applied (e.g. AdobeRGB)
• Import into Photoprism
• Navigate to photo in Photoprism
• Visually compare to original

Expected result: Lower resolution, identical colours.

Actual result: Lower resolution, very noticeable reduction in saturation.

Downloading the thumbnail image and comparing to the original with exiftool shows that the thumbbnail lacks the ICC profile of the original. Copying the ICC profile from the original to the new resolves the problem:

exiftool -icc_profile -b -w icc file.jpg
exiftool "-icc_profile<=file.icc" fit_2048.jpg

[bobobo1618]

As for a solution, it looks like somebody had a similar problem in the past and ended up using libvips via golang bindings. The most mature of these bindings at the moment seems to be govips.

[lastzero]

Great, one more dependency 😂 can take a look at this when we're done with facial recognition and batch edit...

[bobobo1618]

Hmm, another option might be ImageFlow Server. Point it at a bucket of images and you can have it process them with URL query parameters.

That would limit PhotoPrism's role to generating the original previews. It could also potentially write the previews to some cloud storage which ImageFlow could read from, going some way towards facilitating cloud storage, something I've seen asked about a few times.

[lastzero]

related issue with videos: see #1765

[lastzero]

This change converts colors to standard sRGB if an Apple "Display P3" color profile is detected:

• 5be456a

Not sure if color profile conversion also works when originals are HEIF images, needs to be tested.
Videos and file formats other than JPEG haven't been touched yet.

Adding support for additional color profiles should be easy (we can leave that to external contributors).

A small challenge may be profile name comparison: For example "Adobe RGB (1998)" vs just "Adobe RGB". There may be differences or there could be different names for the same profile... research needed.

I'll start a new Development Preview build for testing:

• https://docs.photoprism.org/release-notes/#development-preview