Is ShortPixel Image CDN different than the ShortPixel Image Optimization service? How?
The image CDN and ShortPixel Adaptive Images work on a different model than our standard image optimization service, even 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 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 with this pricing policy:
1 credit = 1 optimized image that is served from our service cache for an unlimited number of times during 30 days.
Our CDN doesn't delete your compressed images from the 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. ShortPixel Adaptive Images service has three components: Image Optimization + Image CDN + Adaptive images.
It spends credits in a similar manner to the Image CDN, but it also count the each image size that is generated for a particular viewport. When a new visitor open a page, it gets properly sized and optimized images for its viewport. These images are stored for 30 days by our CDN and are served to the visitors that have the same viewport during this period. You need one credit ror each genereated, optimized and stored image. After 30 days, the images are deleted from our CDN' cache.