The job is a different container, not a smaller file
A CMS refuses WebP. Your designer handed you WebP. That is this page: pick PNG or JPG, canvas toDataURL at quality 0.95, download. There is no quality slider and no resize slider. If the CMS also has a 200 KB cap, go to the image compressor after (or instead) and use those knobs. I keep the tools separate so “convert to PNG” and “make it 200 KB” do not share a paragraph. Byte size may change as a side effect of the codec. That is not the promise.
JPG has no alpha. A PNG logo on a transparent canvas becomes an opaque rectangle (usually black-filled where alpha was). WebP can keep alpha if the browser’s encoder cooperates; do not assume every Safari vintage agrees. Color profiles get flattened to whatever the canvas thinks RGB is. CMYK source files become RGB-ish. Animated GIF usually becomes the first frame. That last one is the bug report I expect weekly.
Worked example: PNG logo to JPG for a form that “only takes JPG”
If the logo has transparency, stop. You will get a hard box. Flatten onto a white (or brand) background in an editor, then convert, or tell the form to accept PNG. If the logo is already on white, JPG at 0.95 is usually indistinguishable at web sizes and may even be larger than a clean PNG. The form’s rule is political, not technical.
Worked example: camera JPG to WebP for a page that supports it
Same pixels, different codec. Many photos shrink. Some barely move. Check the downloaded size before you celebrate. You still went through a canvas, so this is not a lossless transcode of the original JPEG bitstream. EXIF is usually gone after canvas export. If you needed GPS stripped, good; if you needed to keep camera copyright tags, this is the wrong tool.
Worked example: WebP back to PNG because an email client hates WebP
Convert to PNG. The file may get larger. That is expected: you asked for a widely-decoded still image, not a small one. If the WebP was photographic, PNG will be chubby. If it was a UI graphic with few colors, PNG can be reasonable. Animated WebP or GIF: expect one frame unless you used a dedicated animation tool, which this is not.
What I will not pretend
AVIF depends on the browser; this select list is PNG, JPEG, WebP. ICO and SVG are different jobs (see the favicon generator for the former). RAW from a camera needs a JPG/PNG export first. This is not PDF to image; a PDF page is a document, not an image/* file. HEIC is decode-or-bust in the browser you have today.
ICC profiles and “keep metadata” are not on the menu. Canvas export is RGB pixels. A print JPEG with a CMYK profile will look like a browser preview, then become sRGB-ish PNG/JPG/WebP. If a client’s brand orange shifts, that is color management, not a bug in the select box. For a lossless PNG that must stay a PNG (UI, screenshots with type), converting to JPG “because the other site uses JPG” is how you introduce ringing. Convert only when the destination cannot decode the source codec.
Questions
Is this the image compressor?
No. Format converter swaps PNG/JPG/WebP at a fixed 0.95 with no resize slider. Compressor is quality + resize to hit a byte budget.
Are files uploaded?
No. Canvas encode stays in this tab.
What happens to transparency on JPG?
It is gone. JPG has no alpha. Flatten on a solid background first if you must use JPG.
Will my animated GIF stay animated?
Usually no. Canvas tends to keep a single frame. Test, or use a dedicated GIF tool.
Does the file get smaller?
Sometimes, as a codec side effect. If size is the requirement, use the compressor.
AVIF or HEIC?
Not in the select list. HEIC only works if this browser can decode it into a canvas, which many still cannot.