Choosing An Image Format

Choosing an image format

Picking the best image format for your needs is likely easier than video formats, as there are fewer options with broad support, and each tends to have a specific set of use-cases.

Photographs

Photographs typically fare well with lossy compression (depending on the encoder's configuration). This makes JPEG and WebP good choices for photographs, with JPEG being more compatible but WebP perhaps offering better compression. To maximize quality and minimize download time, consider providing both using a fallback with WebP as the first choice and JPEG as the second. Otherwise, JPEG is the safe choice for compatibility.

Best choice	Fallback
WebP or JPEG	JPEG

Icons

For smaller images such as icons, use a lossless format to avoid loss of detail in a size-constrained image. While lossless WebP is ideal for this purpose, support is not widespread yet, so PNG is a better choice unless you offer a fallback. If your image contains fewer than 256 colors, GIF is an option, although PNG often compresses even smaller with its indexed compression option (PNG-8).

If the icon can be represented using vector graphics, consider SVG, since it scales across various resolutions and sizes, so it's perfect for responsive design. Although SVG support is good, it may be worth offering a PNG fallback for older browsers.

Best choice	Fallback
SVG, Lossless WebP, or PNG	PNG

Screenshots

Unless you're willing to compromise on quality, you should use a lossless format for screenshots. This is particularly important if there's any text in your screenshot, as text easily becomes fuzzy and unclear under lossy compression.

PNG is probably your best bet, but lossless WebP is arguably going to be better compressed.

Best choice	Fallback
Lossless WebP or PNG; JPEG if compression artifacts aren't a concern	PNG or JPEG; GIF for screenshots with low color counts

Diagrams, drawings, and charts

For any image that can be represented using vector graphics, SVG is the best choice. Otherwise, you should use a lossless format like PNG. If you do choose a lossy format, such as JPEG or lossy WebP, carefully weigh the compression level to avoid causing text or other shapes to become fuzzy or unclear.

Best choice	Fallback
SVG	PNG

Providing image fallbacks

While the standard HTML <img> element doesn't support compatibility fallbacks for images, the <picture> element does. <picture> is used as a wrapper for a number of <source> elements, each specifying a version of the image in a different format or under different media conditions, as well as an <img> element which defines where to display the image and the fallback to the default or "most compatible" version.

For example, if you're displaying a diagram best displayed with SVG, but wish to offer a fallback to a PNG or GIF of the diagram, you would do something like this:

<picture>
  <source srcset="diagram.svg" type="image/svg+xml">
  <source srcset="diagram.png" type="image/png">
  <img src="diagram.gif" width="620" height="540"
       alt="Diagram showing the data channels">
</picture>