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Compressing images - Printable Version

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Compressing images - yzerfontein - 09-18-2010 01:00 AM

On advice I've spent some time compressing images using http://www.punypng.com. But I'm still failing the image compression test, for example:

FAILED (108.4 KB, target = 40.9 KB - savings of 67.6 KB)- http://www.southafrica.to/transport/Airlines/SAA-flights/images/20090220/SAA.JPG

What compression tools can I use to achieve the saving of 67.6KB?Huh

RE: Compressing images - pmeenan - 09-18-2010 01:11 AM

Punypng will not do a lossy compression, it just strips and optimizes the existing image. I don't know that there are any automated tools that will do it (and lossy compression is best left to the user right now anyway). The best way is to load the original file in an image editor (Photoshop, Gimp, whatever) and save out the jpeg, lowering the quality as low as you can while keeping the image visually acceptable.

The "standard" we use is to use a quality level of 50 with Photoshop's "save for web" feature but you might be able to do even better manually.

Here is a 37KB version of the file:

And the original 108KB version:

RE: Compressing images - yzerfontein - 09-18-2010 01:34 AM

Thanks! I've got the Gimp & I'll start compressing.

I also got this error WARNING (7.8 KB, target = 6.1 KB - savings of 1.8 KB - Convert PNG to 8 bit)- http://www.southafrica.to/logo/southafrica.png

How do I convert PNG's to 8-bit?

RE: Compressing images - pmeenan - 09-18-2010 01:38 AM

That check is a bit iffy (and I'll get rid of it when we merge the Page Speed and Pagetest checks). It looks like you're doing a fair bit with alpha transparency for that image so it shouldn't be converted to an 8-bit png.

RE: Compressing images - yzerfontein - 09-18-2010 07:14 PM

Thank Patrick, I'm now passing the image compression test Smile