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Image Stack is enabled for a CDN resource in two places:
  • Resource Settings — applies Image Stack to all requests for that resource. Use this only when the origin serves static image assets exclusively. For mixed-content origins, enabling it resource-wide causes conflicts with the Rewrite option.
  • Rules — applies Image Stack to requests matching a specific URL pattern. This is the recommended approach for most resources.
The steps below describe how to enable Image Stack via a rule.
1

Open the CDN resource Rules tab

Open the settings of the required CDN resource and go to Rules. Click Create rule and select Image optimization from the template list.
Create rule dropdown with Image optimization template selected
The rule creation page opens with the pattern /.*\.(jpg|jpeg|png) pre-filled, which targets all JPG and PNG image requests.
2

Configure the Image Stack section

In the Options section, find the Image Stack card and enable the Enable Image Stack checkbox.
Rule creation page showing Image Stack option in the Options section
After enabling, configure the parameters:
Image Stack settings expanded showing Image quality, Compression, and Image Stack overview sections
Image quality — default quality level for delivered images. Four values are available:
  • High: 95%
  • Medium: 80%
  • Low: 65%
  • Custom value: 0–100%
Enable lossless for PNG — delivers PNG images without any quality loss. When enabled, the quality setting has no effect on PNG files.
The quality setting cannot run independently. Enable at least one other option — Compression, Resize, or Crop — alongside Image quality. To set quality per individual image, add the quality query parameter to the image URL. For example: https://image.example.com/image.jpg?fmt=avif&quality=50
Compression — converts JPG and PNG images to WebP or AVIF format. Enable Enable WebP compression, Enable AVIF compression, or both. When both formats are enabled and the browser supports both, images are delivered in AVIF.To apply compression per individual image, add the fmt query parameter to the image URL:
For more details, see image compression.Image Stack overview — the resize and crop operations are configured per image via query parameters. Because each image has unique dimensions and crop coordinates, there are no resource-level defaults for these operations.For query parameter reference, see Crop images and Reduce image size.
3

Save the rule

Click Create rule to save changes. Image Stack becomes active within 5–10 minutes.
When a rule with Image Stack is saved, the resource cache clears automatically and CDN servers begin requesting content from the origin. To prevent origin overload during this period, consider enabling Origin Shielding first or scheduling the change during low-traffic hours.