PNG Format Shows Superb Lossless Compression

[Suhit Gupta]

<div class='os_post_top_link'><a href='http://blogs.zdnet.com/Ou/?p=361' target='_blank'>http://blogs.zdnet.com/Ou/?p=361</a><br /><br /></div><i>"Blogger David Naylor managed to get himself dugg for posting this cool 24-bit bitmap that shows every single color in the 24 bit spectrum. The file is 4094 by 4096 pixels which works out to precisely 16,777,216 pixels which happens to be 2 to the 24 bit power. What's interesting is that such a file takes 48 MBs to store in an uncompressed format yet the PNG compressed file took a mere 58 kilobytes which means PNG compression achieved a 847.5 to 1 LOSSLESS compression ratio! The same file in a minimum-loss JPEG compressed file took 3.84 MBs and this is NOT a lossless format. The moral of the story is that people need to be more aware of the PNG format and stop using JPEG for everything."</i><br /><br />While I post mostly JPG images here on DMT (according to the article - JPEG is more appropriate for Internet distribution of medium and large sized photos of nature or people where you need a good compression ratio with an acceptable loss in image quality), I have started storing personal images in both PNG and JPG formats when converting from RAW. Do you use the PNG file format?

[Jason Dunn]

PNG is cool for some things, but definitely not for complex images like photos. The file sizes are too bloated...

[leslietroyer]

Artificial files are really poor at determining compression ratios for real world image files. Take that same # of bits and randomize their position in the file and the PNG will be much much bigger than the jpg.

Les

[jeffd]

png is great as a compression format so you can work with your pictures unaltered, but jpeg is still best for web pages. This experiment seems to have hit a sweet spot for png, cause more often then not the png is still allways larger then the jpg. Also browser support for inline png is still lacking wich is kind of sad.

[Tom W.M.]

I use PNG for photos when I save any edits to them, often in parallel with the raw XCF (GIMP image file, like PSD). I do notice JPEG compression artifacts on my photos, so I don't want to make the situation any worse, and I want to have a fully portable version of the photo that I can access for years to come (I don't trust XCF for this). Yeah, the files are a bit big, but usually no more than twice the JPEG.

Of course, I use PNG all the time on the web for non-photographic images. I've never heard of "inline png"--you mean PNG alpha transparency? Still, that's only an issue in Internet Explorer &lt;= 6 (it's fixed in 7), and not an issue at all in any other browser. Or did you mean data:... URLs? Yeah, IE is broken there too, but that is the case for any format you might use them for, not just PNG.