I see this problem: I upload a 122KB compressed image After downloading the image to CDN Shopify, it size 220KB. What is the reason?
The screenshot is clear:
Link to download the original image:
Link to this image only in Shopify CDN
Because Shopify recompresses PNG images to 90% quality.
If you want more control over your image compression, use JPG and check the following reference for when and how compression is done by Shopify.
I know this isn't ideal for cases such as yours when you need transparency i.e. using PNG but you may also consider an alternative format that supports transparency and is more size effective than PNG.
Hope this helps!