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I have a large set of png images I am trying to compress and I would like some advice from all of the graphics experts out there :) on the best method to do this. I have access to both a Mac and Windows machine and would like the compressed images to be as small as possible without losing any quality ().

From what I have read it seems that PNGSLIM is the best way for me to go (http://graphicsoptimization.com/blog/?p=7), has anyone used this before and would you recommend it? Or should I just use PNGCRUSH?

Looking forward to learning from your wisdom.

UPDATE: When I tried to download PNGSLIM my virus checkerflagged it up as a dangerous file??

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PNG is a lossless format, so you don't lose any image information (quality) when using the format. Compressions can be changed, etc., but all the image data is still there, assuming it's being done correctly. –  matthewpavkov Sep 29 '11 at 17:23
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PNGs can certainly be lossy if you change the bit-depth when saving. –  DA01 Sep 29 '11 at 17:25
    
That wouldn't really qualify as compression IMO –  horatio Sep 29 '11 at 19:00
    
apropos to what DA01 says in his answer, ( optipng.sourceforge.net/pngtech/optipng.html ) is a nice discussion of the topic which includes a list of programs. –  horatio Sep 29 '11 at 19:33
    
Related question: graphicdesign.stackexchange.com/q/3162/10419 –  porneL Mar 5 '13 at 23:26
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5 Answers

up vote 1 down vote accepted

On the Mac I use PNGCrusher:

http://www.macupdate.com/app/mac/17768/pngcrusher

On Windows I use Optipng:

http://optipng.sourceforge.net/

Both basically strip out all meta information that isn't required by the browser to render it.

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I've also used PNGCrusher on Mac, and it worked great. –  matthewpavkov Sep 29 '11 at 17:30
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More tools:

For me PNGOut seems to be the best, but in a few cases SmushIt produced lower sized images. OptiPNG produced larger files than both.

There's also Google Page Speed, which tells you which images could be optimized...

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The tool you mentioned seems to work great for me (no virus warning). I saw a 44% decrease in file size, after a single test.

You can download here: http://people.bath.ac.uk/ea2aced/tech/png/

It also looks like a newer version may be available, according to the modified dates. I downloaded and ran pngslim091.zip.

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Try these two, both of which are very good:

RIOT - http://luci.criosweb.ro/riot/

PNGGauntlet - http://pnggauntlet.com/

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For Mac I've created ImageOptim which runs all PNG optimization tools on every file and picks the best result.

It includes PNGOUT and all tools that YSmushit and PNGSLIM use, so with single drag'n'drop you have equivalent of applying all the advice of all other answers here :)


If you could sacrifice a little quality, then you could reduce size of PNG images by 60%-70% with lossy PNG compressor ImageAlpha (TinyPNG is equivalent tool you can use on Windows).

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