Instant 8-bit alpha PNG converter

http://www.8bitalpha.com/

by ck2 • 15 years ago

57 26 15 years ago

pedrokost• 15 years ago

Thank you a lot for the tool. I had no idea I could compress PNG so much, without loosing too much quality. I will be a heavy user of this.

ck26• 15 years ago

To clarify, I didn't make this site, just discovered it while googling how to accomplish this without Fireworks.

The "beauty" of 8-bit png is how it degrades acceptably in IE8, IE7 and even IE6.

Try comparing a large round icon in 1-bit alpha (ie. gif) vs 8-bit alpha, it's much much better.

davej2• 15 years ago

IE7 and IE8 can display 32bit (24bit for RGB + 8bit for alpha channel) PNGs fine by the way. IE6, of course, only supports alpha transparency on 8bit PNGs.

etherealG• 15 years ago

aw3c23• 15 years ago

What is the difference to using say optipng?

ck26• 15 years ago

optipng/pngout/pnggauntlet are "only" png optimizers

this site gracefully degrades a png with 24bit alpha transparency to 8bit alpha so you don't have to settle for a gif.

I suspect they are using pngnq http://pornel.net/pngnq and pngquant http://pornel.net/pngquant

Some background here:

http://blogs.sitepoint.com/png8-the-clear-winner/

http://www.ethanandjamie.com/blog/81-png8-transparency-witho...

That site is great because it's so easy, they did some very impressive drag-and-drop code and it makes very high quality output that is as good as Fireworks.

TillE• 15 years ago

Yeah, most of the compression seems to come from converting from RGB to colormap with pngquant.

I wonder if it's possible to do all this with an ImageMagick one-liner.

beej71• 15 years ago

Here's a real example, using a test image that has a lot of different alpha values in it, and a 24-bit alpha channel:

    Original:    87047 bytes
    optipng -o7: 82489 bytes
    this tool:   22585 bytes

The main difference, other than size, is that optipng produced an exact copy of the the original, while this tool is lossy, and threw away a bunch of data from the alpha channel. The win is that for the majority of all web cases, 8 bits of alpha is plenty.

ck26• 15 years ago

Note that it's not perfect for all cases, but it's certainly acceptable for small icons.

Here's a 32x32 icon I converted down to 8-bit alpha and then 1-bit, and then resized the whole group so they could be more closely examined:

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

pornel6• 15 years ago

Actually, making good palette for PNG8+a is very difficult, because in PNG8 alpha is not an additional channel, but property of palette entries. Instead of 256 RGB colors in palette you have 265 RGBA colors, so e.g. red and semitransparent red are two distinct entries.

nathos• 15 years ago

Mac users should check out ImageAlpha for optimizing 8-bit PNGs: http://pornel.net/imagealpha

ck26• 15 years ago

I was actually looking for a Windows equivalent to that when I found this wesite.

hecticjeff• 15 years ago

Source code is available on GitHub: https://github.com/thingsinjars/8bitalpha

pornel6• 15 years ago

I've got improved pngquant that gives significantly better results than original version, gd2 library and often rivals pngnq:

https://github.com/pornel/improved-pngquant

It is a bit slow (converts image several times feeding back result's quality back to the algorithm), but difference in quality is significant:

http://geekhood.net/8bitalpha.png - converted via website

http://geekhood.net/imagealpha0.7.png - converted with pngquant 1.3

pbhjpbhj• 15 years ago

Anyone know of a more recent apt repos for pngquant than 1.0-4 (standard Ubuntu repos)?

pornel6• 15 years ago

I doubt there will be one, as Greg Roelofs doesn't actively maintain it (I have submitted my changes to him long time ago, and the response was he also got other patches and doesn't have time to merge them).

aw3c23• 15 years ago

Any chance to build this with libpng14? I think compiling fails for me because I do have that modern version installed and not libpng12.

pornel6• 15 years ago

It definitely works with 1.4.1, but the bundled Makefile sucks.

Just compile *.c and link it against libpng in whatever way your system requires.

thingsinjars• 15 years ago

Wow, I go on holiday away from a decent internet connection and next thing you know, HN front page. Urk.

Hope it all works well for everyone. As mentioned, the source is all on github (https://github.com/thingsinjars/8bitalpha) so if there are any improvements, fork away.

I'll try and keep an eye on it in case something breaks but I'm a bit limited to an iPhone SSH client on a foreign country's network so play nice. :D

I'm glad people are finding it useful, though.

ck26• 15 years ago

Great work, many thanks for the source.

Ah, now I see it's a far cry from pngng/pngquant

https://github.com/thingsinjars/8bitalpha/raw/master/image.p...

Some php gd2 conversion, gets the job done but it's not as sophisticated.

Still, huge potential to slide in other solutions, even via shell.

Instant 8-bit alpha PNG converter

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