PageSpeed Service was turned off on August 3rd, 2015. Please see Turndown Information for PageSpeed Service.
Reduce payload size of image resources by re-compressing images optimally, removing unnecessary headers and minimizing reflows.
This rewriter implements the PageSpeed rule for minimizing payload size.
Optimize Images rewriter re-scales, re-compresses, optimizes huffman tables
for JPEG images, strips metadata, color profile information. This
reduces the number of bytes downloaded, often substantially. When no size gains
are realized, the rewriter leaves the original image unaltered. Image rewriting
is particularly useful on image-heavy pages that have not been optimized
offline. As a result of rewriting, the visual quality of images
should not degrade in any perceptible way.
The compelete list of options that are supported under this rewriter are as follows:
Convert JPEG to WebP (Lossy Optimization)
When this options is selected, PSS converts JPEG images to WebP and serves those WebP images to modern browsers that support the image format. Optimized JPEG images will continue to be served to older browsers.
Convert PNG & GIF to JPEG (Lossy Optimization)
When this option is selected, PSS converts PNG and GIF images to JPEG images without any visual degradation of the image quality.
Re-compress JPEG (Lossy Optimization)
When this option is selected, PSS will re-compress the JPEG images with the specified quality. This also strips of unnecessary image metadata like thumbnails.
Add Image dimensions (Lossless Optimization)
When this options is selected, PSS inserts
height= attributes into
<img> tags that lack them and
sets them to the image width and height. This will help in reducing the number
of reflows that happens when a web page is loaded thereby improving the user
Progressive JPEG (Lossless Optimization)
When this option in selected, PSS converts JPEG images to progressive JPEG images, which helps in reducing the numbers of bytes served on the wire and improving the user experience by loading images incrementally.
Re-compress PNG (Lossless Optimization)
When this option is selected, PSS will re-compress PNG images by removing optional PNG segments like iTXt, hIST, etc. and applying various PNG optimization techniques like stripping alpha channel if the image is not transparent, reducing the bit depths, converting true color images to indexed images if there are less than 256 colors, etc.
Remove meta data (Lossless Optimization)
When this option is selected, PSS will remove EXIF related information from the image files.
Remove color profile (Lossless Optimization)
When this option is selected, PSS will remove color profile information from the image files
Resize on Server (Lossy Optimization)
Images are often resized in the browser because of specified size attributes that are smaller than the original image size. When this rewriter option is selected, PSS will reduce the size of each image on the server to the appropriate value before serving. This lowers page latency in two ways. First, fewer bytes are downloaded by the browser because the image size is smaller. And second, the browser has to do less processing because it need not resize the image before rendering.
Resize using rendered dimensions on Server (Lossy optimization)
When this rewriter option is selected, PSS will reduce the size of each image
to the dimensions of the rendered image in a browser. If the
same image appears more than once on the page and with different rendered
dimensions, it resizes the image to the biggest of its rendered dimensions.
ImageResize, this rewriter will lower the
page latency by reducing the bytes downloaded by the browser and reducing the
processing on the browser.
Optimize Images is applied on images referenced
<img> tags and if Minify CSS is
enabled, then images referenced from
list-style-image and list-style CSS properties will also be optimized.
This rewriter is applied on all images served from the PageSpeed Service (either CNAME’d or proxied).
Limitations mentioned for the Proxy Images rewriter are also applicable to this rewriter.