This rule triggers when PageSpeed Insights detects that the images on the page can be optimized to reduce their size without significantly impacting their visual quality.
OverviewKeep image sizes to a minimum to reduce the amount of time a user is waiting for resources to load. Properly formatting and compressing images can save many bytes of data. This saves time for users on slow connections and money for users on limited data plans.
You should perform both basic and advanced optimization on all images. Basic optimization includes cropping unnecessary space, reducing color depth to the lowest acceptable level, removing image comments, and saving the image to an appropriate format. You can perform basic optimization with any image editing program, such as GIMP. Advanced optimization involves further (lossless) compression of JPEG and PNG files.
Use an image compressor
Several tools are available that perform further, lossless
compression on JPEG and PNG files, with no effect on image quality. For
JPEG, we recommend jpegtran
(available on Linux only; run with the
option). For PNG, we recommend OptiPNG
Choose an appropriate image file format
You should test which format is best for your image, although we some high level recommendations here:
- PNGs are almost always superior to GIFs, although some older versions of browsers may only have partial support for PNG.
- Use GIFs for very small or simple graphics (e.g. less than 10x10 pixels, or a color palette of less than 3 colors) and for images which contain animation.
- Use JPGs for all photographic-style images.
- Do not use BMPs or TIFFs.