PNG, JPG, WebP — convert without surprises

How to use

1. Drop an image. The tool tells you whether it contains any transparent pixels.
2. Pick the target format.
3. For JPG, choose the background colour that transparent areas will sit on. For PNG and WebP you can keep transparency or flatten it.
4. Adjust quality for JPG and WebP, compare with the slider, and download.

How it works

The file is decoded by the browser, drawn onto a canvas and re-encoded with canvas.toBlob. Transparency is checked by scanning the alpha byte of every pixel; a single value below 255 means the image has transparent or semi-transparent areas.

JPG cannot store an alpha channel. Before encoding, the canvas is filled with your background colour and the image is composited on top, which for each channel computes out = src × α + background × (1 − α). Without this step browsers turn transparent pixels black.

PNG is lossless, so the quality slider is hidden for it. WebP supports both transparency and lossy compression.

Worked example

A 50%-transparent red pixel (255, 0, 0, α = 0.5) converted to JPG on white becomes 255 × 0.5 + 255 × 0.5 = 255 red, and 0 × 0.5 + 255 × 0.5 ≈ 128 for green and blue: a pink of (255, 128, 128). On a black background the same pixel becomes (128, 0, 0).

Limitations

• Only the first frame of animated GIF or WebP files is converted.
• Output is 8-bit sRGB; 16-bit PNGs and wide-gamut images are reduced.
• HEIC/HEIF input works only in browsers that can decode it natively (mainly Safari).
• Converting a JPG to PNG does not restore detail lost to the original compression; it only makes the file larger.

FAQ