About PNG to JPG
This is the most worthwhile image conversion there is, because PNG is the format people most often end up with by accident and least often actually need.
PNG is lossless. Every pixel is stored exactly, which is correct for screenshots, logos and diagrams, and badly wrong for photographs. A photograph contains sensor noise, and noise is almost incompressible when you are forbidden from discarding any of it. The result is that a photo saved as PNG is routinely five to ten times larger than the same image as a JPG, with no visible difference at all.
If a website is slow and its images are PNGs, that is usually the whole story.
When to make this conversion. Any photograph. Anything with gradients, skies, skin tones or continuous colour. Camera output, phone screenshots of photos, exported design comps of photographic content — all of these belong as JPG.
When not to. Screenshots of text and UI, where JPG's compression puts visible halos around the sharp edges of glyphs and often produces a *larger* file than PNG. Logos and line art, for the same reason. Anything needing transparency.
Transparency is the one real trap. JPG has no alpha channel, so transparent areas have to become something. We paint them white, which is almost always what people expect. A naive conversion makes them black, which is why logos converted elsewhere sometimes come back looking burnt. If you need the transparency kept, convert to WebP instead — it is smaller than PNG and keeps alpha.
On quality. 90 is the default and is visually indistinguishable from the original for almost any photograph. Dropping to 80 roughly halves the size again and is what most websites should ship. Below 60 you will start to see blocking in flat areas.
The conversion runs in your browser, so nothing is uploaded and there is no size queue.
Questions
Will converting PNG to JPG lose quality?
JPG is lossy, so technically yes — but at quality 90 the difference is invisible for photographs while the file is several times smaller. For screenshots and line art, stay with PNG.
What happens to transparent areas?
They become white. JPG has no transparency. If you need it preserved, convert to WebP instead.
Are my images uploaded?
No. Conversion happens in your browser using its built-in codecs. Nothing is transmitted.
Why is my PNG so large in the first place?
PNG stores every pixel exactly. Photographs contain noise, which cannot be compressed losslessly, so photographic PNGs are enormous compared to JPG.