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starbase1
04-09-2008, 12:51 AM
I want to check some stuff about PNG formats.

Is every form of PNG compression lossless? In which case why not use maximum all the time? I also took a look at the wikipedia entry, and was a bit surprised to see that different levels of compression were achieved by different programs.

Can anyone advise on how to get the best compression in practice? I'd rather not have to try them all one by one!

I understand that this would only save disk space, not memory...

Thanks, Nick

JeffrySG
04-09-2008, 09:20 AM
I only use Photoshop for saving my PNG files. I only see the option for interlaced and non-interlaced. I've always found Interlaced to be larger in file size, but they are both saving compressed/lossless. I would think that the interlaced just has to do with the way the file loads/displays.

What app. are you using that you have different compression options?

K-Dawg
04-09-2008, 09:51 AM
Interlaced or not effects on how the image gets loaded on the web. Interlaced means when it gets loaded you see the whole image but in bad quality and as the information gets transfered over thenet and the image builds up you see it better and better. Non-interlaced loads the image from top to bottom at once building the image as the information gets transfered.

Thats all with it.

Generally .png saves compressed but lossless so you will not have any quality issues but smaller file sizes.

If you save out of LW then don't use PNG32 or you will embed the alpha and .png doesn't act like .tga etc with embedded alpha. You will not have access to the alpha.

Greetz

Scazzino
04-09-2008, 10:11 AM
I want to check some stuff about PNG formats.

Is every form of PNG compression lossless? In which case why not use maximum all the time? I also took a look at the wikipedia entry, and was a bit surprised to see that different levels of compression were achieved by different programs.

Can anyone advise on how to get the best compression in practice? I'd rather not have to try them all one by one!

I understand that this would only save disk space, not memory...

Thanks, Nick

PNG is a lossless format, by definition... However, to achieve greater compression, some applications may pre-process an image in a lossless format before actually saving it out as a PNG...

Here's some information I wrote in a chapter for the FreeHand Bible a few years ago about the various lossy/lossless formats for web images... PNG is the last format covered...
http://dreamlight.com/insights/06/graphics.html

starbase1
04-09-2008, 11:45 AM
Thanks all - has anyone tried PNG optimizers?

Jarno
04-09-2008, 06:44 PM
The compression in PNG is based on gzip. Zip-like compression algorithms to have a compression factor control, which basically determines how much hard work it does. That used to be important when computers were slow and compressing large files could take minutes. But these days it's pretty pointless.

---JvdL---