问题
I read some articles about HTTP headers compression. Today I installed YSlow and it recommends that I compress the resources (text/html, javascript, css and images). Now I'm reading the documentation for Apache mod_deflate but in the example don't compress images.
Should I or should I not compress images in my site?
回答1:
Your images should already be compressed - any extra compression won't have any noticeable effect on filesize, but will increase processing time.
- .png files use DEFLATE compression already.
- .jpg files generally use lossy compression.
- .gif files use LZW compression.
Compressing files that have already been compressed very rarely results in a reduction in filesize, and can often increase filesize.
回答2:
Images such as GIF, JPEG or PNG are already compressed via highly specialized algorithms that achieve better result than general purpose algorithms such as deflate.
Therefore, re-compressing them yields little to no gain in size, and can even make files bigger, with the added cost of server-side processing.
So, in other words... do not compress images.
来源：https://stackoverflow.com/questions/4957172/why-i-should-not-compress-images-in-http-headers