Recommend export settings for Nextcloud albums

Software darktable
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For the family album, I’ve been exporting my photos in Darktable to JPEG (8-bit) format at 90% quality. The images are organized into albums online using Nextcloud. But I’m reaching the limits of my available storage space. Typically, each *.jpg export creates a file ranging from about 20MB to 38MB. I haven’t paid much attention to this before, but I now realize that’s a lot. It quickly adds up to a few GB. If I reduce the quality to 85%, the files are just under 25% of the size compared to the 90% quality export. At least on the web, I don’t see any difference at first glance.

Since some family members occasionally create a photo book from the pictures, I’m not sure how the quality will hold up in print. I won’t know for sure until it’s too late. But if I can’t tell the difference at 100% zoom, I’m hoping the print quality will be at least acceptably similar.

According to Google Page Speed Insights, it’s recommended to use WebP with a quality of 80%. The resulting files are now only 20% as large as the 90% JPEG exports. I notice slight differences, especially with smooth color gradients, bokeh, and similar elements. There are subtle variations and color shifts, but hardly any artifacts. If I don’t know the original, it doesn’t stand out. But it does in a direct comparison. I can’t estimate how this will affect the print as a photo book. What I do see, however, is a significantly longer export time.

Question for the community: What would you recommend? Stick with 8-bit JPEG and set the quality to just 85% (or less), or switch to WebP with 80% quality? Maybe you have another or better idea?

BTW: One additional question. Pixel dimensions of the photos are usually huge in my case. I don’t scale down the pictures during export, because i don’t know how to do that. Some photos are landscape, some portrait, some are cropped, some not. So every photo can have a other resolution. What should i use to have a max resolution of 2560x1440 Pixel and keep the aspect ratio of landscape and portrait and cropped images. I don’t want to upscale images, only downscale, when they are bigger as the max resolution. I don’t understand the documentation of the setting.

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Set the maximum dimensions you want in the export module. Darktable will scale the images, such that they fit within that rectangle, possibly not filling one of the dimensions.

This respects the crop and aspect ratio you defined (so the scaling factor will be different for cropped images, which is what you want). It does mean images in portrait orientation will be a lot narrower than landscape orientation, as both are scaled to the height you define, again what you want for display on a (fixed) screen or a book (in most situations).

To avoid upscaling, just set the option “allow upscaling” to “no”. That means the dimensions you gave will be upper limits, and the exported images may be smaller.

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For external storage to display on screen I would limit to Full HD (1920 x 1080) and 85% Jpeg quality. If you need to print you can always export a new version with full resolution at 95% jpeg quality.

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I do, actually: JPEG XL: Superior Image Compression

But it’s controversial: Anyone switched to jxl yet?

TL;DR: At the moment, Safari, Opera, Chrome (with a switch) and Firefox Nightly (with a switch) are the only browsers to support jxl, but that should be enough. Apart from the browsers, the OSes support it natively; there are viewers and you can always convert them back to TIFFs or jpegs.

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Unfortunately Nextcloud itself and specially the memories app, can’t handle jxl. I’m happy that it handles webp and with some extra config, can create webp thumbnails.

The family members which create the photo album, never message me, that they want create a printed photo book. They see the pictures, complain that there are to much interesting from the last vacation and create the book :slight_smile: