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I'm getting a message from PageSpeed Insights that recommends to compress some png images. E.g:

If compressing .../logo.png without loosing information, you would save 1.014 B (12% redcuction).

However, I've compressed the image with "Save for web" option and with the maximum compression. Tried to compress more times, but the image is never compressed more than about 200B. I could compress with PNG-8, but then I'm loosing image quality.

All other formats seem to be well compressed by Gimp with the same option. Any idea of why it's happening and how to solve it?

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    PageSpeed is a red herring you know. Just because things load at one speed for their service, you can't tell what the other bazillion web users load times are. It's best to simply limit HTTP requests as much as possible. – Scott Jul 14 '14 at 9:19
  • I've found a web site where png images are better compressed: tinypng.com – Manolo Jul 14 '14 at 9:55
  • There's something wrong here. Also did you mean KB (kilobytes) and not B (bytes)? A 1.014 KB saving for a 200 KB file is actually a 1.014/200*100=0.5% reduction. – Billy Kerr Apr 3 at 8:52
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GIMP is quite good in PNG compression, but not the best.

To get a basic idea about PNG optimization, read File size and optimization software chapter in "Portable Network Graphics" article on Wikipedia.

I have optimized thousands of PNGs and I recommend these tools for a lossless optimization: PNGOUT, ZopfliPNG.

If you want to make your files even smaller, consider conversion from RGB to indexed, using pngquant. It is lossy but still gives very good results. After this conversion, do the optimization with PNGOUT or ZopfliPNG.

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If you have SU access on your Linux server, you can actually run JPEGOptim and OptiPNG on a cron task so all of your image files are automatically compressed/optimized and you don't even have to think or worry about it once it's setup.

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