Page Speed: Optimize images More Recommendations

Rule Summary

Images
High
Moderate
73%

Overview

Properly formatting and compressing images can save many bytes of data.

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Details from Google

Images saved from programs like Fireworks can contain kilobytes of extra comments, and use too many colors, even though a reduction in the color palette may not perceptibly reduce image quality. Improperly optimized images can take up more space than they need to; for users on slow connections, it is especially important to keep image sizes to a minimum.

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. You should see a benefit for any image file that can be reduced by 25 bytes or more (less than this will not result in any appreciable performance gain).

recommends:

Choose an appropriate image file format

The type of an image can have a drastic impact on the file size. Use these guidelines:

  • PNGs are almost always superior to GIFs and are usually the best choice. IE 4.0b1+, Mac IE 5.0+, Opera 3.51+ and Netscape 4.04+ as well as all versions of Safari and Firefox fully support PNG, including transparency. IE versions 4 to 6 don't support alpha channel transparency (partial transparency) but they support 256-color-or-less PNGs with 1-bit transparency (the same that is supported for GIFs). IE 7 and 8 support alpha transparent PNGs except when an alpha opacity filter is applied to the element. You can generate or convert suitable PNGs with GIMP by using "Indexed" rather than "RGB" mode. If you must maintain compatibility with 3.x-level browsers, serve an alternate GIF to those browsers.
  • 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. If you think an image might compress better as a GIF, try it as a PNG and a GIF and pick the smaller.
  • Use JPGs for all photographic-style images.
  • Do not use BMPs or TIFFs.
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 or jpegoptim (available on Linux only; run with the --strip-all option). For PNG, we recommend OptiPNG or PNGOUT.

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