A 3D render leaves the render engine as a PNG, because that is what the framebuffer writes by default. PNG is lossless, which is correct for a file you will still be editing, and completely wrong for one you are publishing: a 4K exterior render as PNG is commonly 15-40 MB, and no portfolio page or submission portal wants that. Converting to JPEG or WebP at a sensible quality cuts that by 90% or more with no visible change at the size the image is actually displayed. The complication is that renders are synthetic and therefore compress differently from photographs. Large flat areas of single colour — a white render, an untextured massing model, a flat sky — can show visible blocking at settings that would be invisible on real photography, while the foliage, gravel and people cutouts tolerate a lot more. So a single global setting rarely works across a project. There is also the alpha channel question: a render with a transparent background saved as JPEG silently loses transparency and lands on white or black, which is usually the wrong answer for a diagram or a product visual. Skwish handles PNG, JPG and WebP in the browser with a before/after readout per file, so you can compare a PNG-to-WebP conversion against the original before committing the whole set, then export the batch as a ZIP. Nothing is uploaded.