Cf_polish=not_needed on huge images

Why do I get cf_polish=not_needed on large images? For instance: https://assets.thejewelleryroom.com/wp-content/uploads/2019/05/OLC-23.png - if I manually convert it to webp it’s size gets from 473kb to 160kb… so I wonder why cf think’s its not needed.

Also PageSpeed Insights says: " Serve images in next-gen formats. Image formats like JPEG 2000, JPEG XR, and WebP often provide better compression than PNG or JPEG, which means faster downloads and less data consumption." - but I guess having enabled Polish for whole domain should fix this right?

Photographic images, such as the one in your link, should always be compressed using JPEG or, now WebP (and soon, AVIF) for the Web. Your image is photographic in nature but was saved at the origin with the PNG format.

Polish assumes PNGs should be optimized in lossless mode, which would not result in a smaller image, therefore the “not_needed” header value. If you simply save your photo images as JPEGs, you’ll already see a big reduction in file size, and most likely Polish will reduce them even further when converting to WebP.

Polish has two modes: lossless and lossy . In lossless mode, JPEG images are optimized to remove unnecessary data, but the image displayed is unchanged. In lossy mode, Polish reduces the quality of JPEG images in a way that should not have a significant visible effect, but allows it to further reduce the size of the image data.(…) These modes do not affect PNGs and GIFs, as these are lossless formats and so Polish will preserve images in those formats exactly.

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Thanks for your prompt reply. I will read into AVIF as well - sounds interesting!:slight_smile:

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