Compress JPG, PNG, or WebP: choose the right format

SlimPic guide · Updated September 29, 2026

The output format affects file size, transparency, and compatibility. Choose based on the image and where you will use it, rather than changing the filename extension.

JPG and JPEG for everyday photos

JPG and JPEG are two extensions for the same format. JPEG is useful for portraits, landscapes, and product photos. It uses lossy compression, so very low quality may produce visible blocks or smudges. Start from your original when recompressing rather than repeatedly compressing a smaller copy.

JPEG does not support transparency. SlimPic fills transparent areas with white when you choose JPG. For a logo with a transparent background, use PNG or WebP.

PNG for transparency and sharp edges

PNG can preserve crisp lines and transparent backgrounds, but photographic PNGs may be large. Browser PNG encoders do not respond to a JPEG-style quality slider. When keeping PNG, SlimPic may need to reduce dimensions to reach your target. Resizing is not pixel-for-pixel lossless.

WebP for photos and transparent images

WebP supports compressed photos and transparency. Auto mode optimizes PNG and WebP inputs as WebP. Check that your destination accepts WebP; some application forms only allow JPG or PNG. If your browser cannot encode WebP, Auto mode falls back to PNG.

Changing an extension is not conversion

Renaming .png to .jpg does not change the underlying format. Choose JPG in advanced settings to encode a real JPEG. Check the output format in the result. Auto mode may preserve an already-small original, so explicitly select a format when one is required.

Special cases

For text-heavy screenshots, check small text after compression. Animated PNG and WebP may become a still image during processing. HEIC is not supported: export a JPEG from your device first. Simply changing its extension will not work.