This rule is triggered when PageSpeed Insights detects that a picture on a Web page can be optimized to reduce its size without significantly affecting its visual effect.

Minimize the picture size to reduce the time users wait for resources to load. Formatting and compressing pictures properly can save a lot of data byte space. This saves time for users with slower network connections and costs for users with limited traffic packages.

You should perform basic and advanced optimizations for all pictures. Basic optimizations include cropping unnecessary areas, reducing color depth to the lowest acceptable level, removing picture comments, and saving pictures in the appropriate format. You can use any picture editing program (for example,GIMP). Advanced optimizations include further compression (lossless compression) of JPEG and PNG files.

Using the Picture Compression Tool

There are many tools available for further lossless compression of JPEG and PNG files without any impact on image quality. For JPEG files, we recommend that you use thejpegtran或jpegoptim(Linux only; Use--strip-all選項(xiàng)運(yùn)行）。對于PNG文件，我們建議使用OptiPNG或PNGOUT.

Choose the appropriate picture file format

您應(yīng)測試一下哪種格式最適合您的圖片，盡管我們在下面推薦了一些較高級(jí)別的格式：

• PNG格式幾乎一直優(yōu)于GIF格式，盡管某些舊版瀏覽器只能為PNG格式提供部分支持。
• Use the GIF format for smaller or simpler graphics (for example, graphics less than 10x10 pixels or graphics with a palette less than 3 colors) and pictures that contain animations.
• 為所有攝影風(fēng)格的圖片使用JPG格式。
• 請勿使用BMP格式或TIFF格式。

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