Is ShortPixel Image CDN different than the ShortPixel Image Optimization service? How?
The image CDN and the ShortPixel Adaptive Images plugin work on a different model than our standard image optimization service, even if they use the same credits.
1. Our WP plugin and other image optimization tools pull the images to our servers, process them and then put the optimized images back on the users' servers. Each image goes through this process only once and afterwards it remains compressed.
We spend the server resources for compression only once.
2. On the other hand, the Image CDN service (within the Autoptimize plugin) compresses the images and stores them on our service cache for 30 days, and it serves them unlimited times (for each visitor that opens a webpage with the images served through the CDN).
This process continuously uses a lot of resources. We didn't want to measure the traffic and limit it - that's why we came up with this pricing policy:
1 credit = 1 optimized image that is served from our service cache for an unlimited number of times for 30 days
Our CDN doesn't delete your compressed images from your server. Moreover, if your images are already optimized, then our suggestion is to set a softer compression method for the Image CDN: Glossy or Lossless.
3. The ShortPixel Adaptive Images service has these components: Image Optimization + Image CDN + Adaptive images + Smart Cropping.
It spends credits in a manner similar to the Image CDN, but it also counts each image size that is generated for a particular view-port. When a new visitor opens a page, the image gets properly sized and optimized for their viewport. These images are stored for 30 days by our CDN and during this period, they are served to the visitors that have the same viewports. You need one credit for each generated, optimized and stored image. After 30 days, the images are deleted from our CDN's cache.
Important: We recommend you use only one service that has a CDN component.