Hello,
what I’ve learned from the upload of my sketch image to the NSFW gallery section, the website seems to convert every other file format into JPEG format, seems to compress the file size if the original file size exceeds a certain threshold MB size and also seems to shrink the image if the original image dimensions exceed certain dimension thresholds. If that happens, the results can be quality loss and showing up of pixelations and structures which were not in the original image.
Presumably it will be best to save the image as a JPEG for uploading in the forum Artwork section.
Can someone please tell me the thresholds for file size (MB) and for image size (pixel dimensions for width and height) that should not be exceeded to make sure that those things don’t happen when uploading a picture and that the image can be seen on the website and in the browser without significant quality loss?
@raghukamath would be the best person to give advice about this.
Hi @Kronos
The maximum file size is - 3 MB
The maximum megapixels is 9 megapixels
All png are converted to jpg at 95% quality
All jpg are recompressed if possible (the software determines what is necessary) at 99% quality
But all posts will retain original image if you click on the image to open the lightbox there you will see the link to original image. Users can see the original uncompressed images from this feature.
@raghukamath Great, thanks! 
Hm I just checked on some of my own, and I get the same butchered image with “original image” link, not the one I uploaded.
For example this one: Yin and Yang Fairies
I know for sure the original is a 1920x1920 jpeg with 603KiB size, so well below the limits, yet people can only see the a 221KB version with lots of compression artifacts 
Is there something else the jpeg must do?
Though I already tried some things like sticking with the default chroma subsampling, using progressive…always got butchered.
Was the original a png image or a jpg image?
jpg, I usually avoid PNG for any uploads unless it’s something with lots of flat colors that compresses well (like UI screenshots).
I think the jpg is compressed again at 99%. May be we can switch it off. Edit i have disabled jpg compression. can you try to upload one now?
Hm I just uploaded a closeup of my last piece:
But it still got re-encoded at much lower quality, original was 690KiB (that’s 92% quality in Krita, “1x1, 1x1, 1x1” subsampling).
Whatever those 99% in discourse mean, it’s much lower than libjpeg…
I have switched it off now, it should not compress it and just use the original
I noticed the compression a few months ago - I was discussing it with sooz in my urban scene thread:
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