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Comment by simonsarris | Hacker News Reader

Wow it took my png from 659 bytes to 681 and lets me download the 681 byte one. :(

So I took a PNG from wikipedia:

221.0kb (its actually 215 KB or a little more than 220,000 bytes) to a claimed 47.8 KB (really 46.7 KB). Nice!

Running PNGGauntlet, a lossless compression app, with the same file compressed nothing. Wise wikipedians must have already done that.

But the results from tinypng look awful. Here you can flip between the original and the compressed:

http://upload.wikimedia.org/wikipedia/commons/4/47/PNG_trans...

http://i.imgur.com/QOLo3.png

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I wouldn't say they look awful, there's a difference in the background part of the image but the main focus has little change.

It's a trade-off, but I would imagine that if there's thousands of files it could be a significant savings on bandwidth, and you could always keep the original for download but not display puroses.

There's very clear posterization in the yellow die and in the green die's highlights.

That shouldn't be surprising -- high color depth images need more than 256 colors to represent their image with fidelity.

See more: http://en.wikipedia.org/wiki/Posterization

Here are the results of pngnq which does exactly the same thing as this tool. It created a file size of 46K, (which I was then able to reduce to 41K with pngout followed by advpng).

http://i.imgur.com/VPc2k.png

http://pngnq.sourceforge.net/

256 colors may simply not be enough for this image.

(Incidentally I was able to slightly reduce your image to 46K with pngout.)

Riot[1] (windows) does as good or better than pnggauntlet and lets you preview things. supports the same backends I think (pngout, optipng, advpng, etc) and some extra dithering options... perhaps worth a look, I switched from pnggauntlet. :)

[1] http://luci.criosweb.ro/riot/

There are _slight_ artifacts on the defocused green die. At typical Wikipedia in-article display sizes (400x300, in this case), this is acceptable. Viewing in Win Firefox 13.01, Windows gamma. I'd use tinypng on large files before downscaling for web use.

Use it after downscaling not before.

If you have a good downscaling tool it will create a larger number of intermediate colors when you downscale and you'll actually end up with a larger image!

Good point.

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