Choosing an image format is a trade-off between file size, quality and features such as transparency. Here is a practical way to decide.
The short answer
| Use | Best format | Why |
|---|---|---|
| Photos on websites and in stores | JPG or WebP | Small files with good quality |
| Logos, icons, screenshots, text | PNG (or WebP) | Sharp edges and flat colours stay exact |
| Anything that needs a transparent background | PNG or WebP | JPG can't store transparency |
| Email images | JPG for photos, PNG for text-heavy blocks | Both work in practically every email app |
JPG: the photo format
JPG (also written JPEG) uses lossy compression: it throws away detail the eye is unlikely to notice, which makes photos much smaller. A quality setting controls the trade-off: higher quality keeps more detail and makes bigger files.
JPG has no transparency. When you convert a transparent image to JPG, the transparent areas must be filled with a colour. In the image converter you choose that colour; nothing is filled without telling you.
PNG: exact pixels
PNG is lossless: every pixel is stored exactly. That keeps text, logos and screenshots crisp, and PNG supports transparency. The downside is size: a photo saved as PNG is usually several times bigger than the same photo as JPG.
That is also why "compressing" a photo PNG has limits. The image compressor can store PNGs more efficiently and, at its Balanced level, round colours very slightly in a way that is invisible on photos, but for big savings on photos, JPG or WebP is the better choice.
WebP: small files with transparency
WebP supports both lossy and lossless compression and transparency. For the same visual quality it is usually smaller than JPG and PNG. Modern browsers display WebP; some older tools and email apps may not, so check where the image will be used.
GIF: animation only
GIF is limited to 256 colours per frame. Today it is mainly used for simple animations. Note that converting a GIF to another format keeps only the first frame.
Quick decision guide
- Does it need transparency? Use PNG or WebP.
- Is it a photo? Use JPG (or WebP for the web).
- Is it text, a logo or a screenshot? Use PNG.
- Is file size critical? Try WebP, then compare the result with the original in the image compressor.