webp-to-png conversion
As Danbooru does not support the .webp format and scanners often employ it for its efficient compression, users will often have to reformat the image or a portion of it to be able to upload. While WEBP features lossless compression it is most frequently ignored in exchange for its great reduction in filesize when utilized under lossy compression.
Unless the resulting filesize would surpass the 50MB limit it is often better to convert the WEBP files to PNG, otherwise the JPEG conversion would degrade the image further.