Pixelfed

479 readers

1 users here now

The official Pixelfed lemmy community

Project website

founded 2 years ago

MODERATORS

dansup@lemmy.world

Pixelfed maximum quality defaults (github.com)

submitted 5 months ago by Glitterkoe@lemmy.world to c/pixelfed@lemmy.world

3 comments fedilink hide all child comments

TL; DR; PNG resized to 1080 pixels on the short edge.

Just recently started dabbling with Pixelfed, but I couldn't find the best upload settings anywhere in the documentation, bar the 15MB upload limit. The server documentation states a quality percentage to use and boolean switches whether to resize and/or optimize images using aforementioned quality.

Turns out: images are by default resized to fit 1080 pixels on the short edge and are re-encoded using https://image.intervention.io/v2/api/encode set to the server's chosen quality percentage (which usually isn't advertised for instances but is 80 by default). Luckily, PNG is accepted nearly everywhere and its compression is lossless.

Those PNGs are way bigger than actual full resolution WebP's with a quality over 80% for my 24MP RAW exports. Most resized and optimized images tend to be smaller than 1MB, though, whereas the allowed PNG's are just shy of 3MB.

A full-res 24MP test image on 85% quality WebP dives well under that 3MB. Restricting to something more modern say 4K monitor resolution at 85% WebP would be well within current optimized file size ranges of about 1MB from my experiments with Darktable exports.

top 3 comments

sorted by: hot top controversial new old

[–] RagingHungryPanda@piefed.social 2 points 5 months ago (1 children)

hey there and thanks for sharing your findings. I'm also trying to get set up with an instance and am using the 80%, but explicitly. Did you do something to convert PNGs to WebP or are we stuck with the resizing?

I'm just using

MAX_PHOTO_SIZE=20000  
MAX_ALBUM_LENGTH=15  
IMAGE_QUALITY=80

as the only restrictions. But really, my instance isn't really a photographer blog, so super high res images probably wouldn't be necessary.

Looking at the source code you linked, all photos are getting resized anyway? Should we expect that a PNG upload will typically be about 3MB? Thanks for sharing :)

[–] Glitterkoe@lemmy.world 2 points 5 months ago (1 children)

Well, from what I understand for admins you have some config keys being PF_OPTIMIZE_IMAGES to toggle the entire optimization pipeline (or accept supported formats as is) and the IMAGE_QUALITY percentage as an integer to tweak the lossy compression for formats that support it.

The image resize to 1080 is even hardcoded in the optimizrtion pipeline. I think I saw a toggle for it on the PHP side, but it seems they only expose the toggling of storage optimization as a whole for admins. The 1080 is currently not exposed as a parameter to set, sadly.

As a creator, I was interested in the maximum possible quality to retain. As PNG is often supported and by design only features lossless compression at best while remaining well under 15MB for a file with common image aspect ratio's, that was the winner in that regard. My uncropped 24MP images then become 3MB-ish.

Other formats tend to be way smaller in filesize due to lossy compression being so effective and most images I checked on Pixelfed are resized&optimized JPEGs well under 1MB (around 600-800KB). That is probably the file format and size you'll encounter most.

My own filesize comparisons were for RAW exports using Darktable for different file formats, qualities and resolutions. The PHP image pipeline used by Pixelfed will probably yield comparable results for the same image.

If I were to advocate new settings, that would be cranking up the resolution to more modern standards (like fitting a 4k monitor) and converting to WebP at some 85% (or sticking with 80%).

It's difficult, though, as that may introduce double-lossy pipelines when converting other lossy formats. That's why I looked into resolution settings first. If you upload an image that is too large, it currently decodes your (maybe lossy) image, resizes that (lossy, probably?) and re-encodes that using the set lossy quality if applicable.

Thus, first order of business: at least publish ideal image sizes.

Second, better quality control. Might involve settings per file format or setting a unified output file format.

[–] RagingHungryPanda@piefed.social 2 points 5 months ago

that's a good explanation, thank you very much 👍