Why is there a compression level for PNG images?

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pstein
Posts: 51
Joined: Mon Sep 04, 2006 3:43 pm

Why is there a compression level for PNG images?

Post by pstein » Mon May 26, 2008 7:25 pm

When I save a picture as .PNG then the options how a compression level for .PNG format.

Why?

I thought PNG is lossless and hence has NO more-or-less compression but the best one.
It is the first time that I have seen such a level for PNG in all the image editor prgms.

Peter

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XnTriq
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Post by XnTriq » Mon May 26, 2008 9:20 pm

Jens Brückmann ([url=http://www.j-a-b.net/web/graf/png-compression]PNG Compression Rates[/url]) wrote:PNG compression is able to considerable reduce the file size of an image without any loss of quality. While the jpg compression is quite lossy, in png compression there is neither a change of colours nor a reduction of colour depth. The number of colours exactly remains the same.

Ten steps of compression can be used for png images. Below is shown, how an image with maximum amount[1] of possible colours is compressed from a file size of about 197kB, which is roughly the same as the corresponding bmp file size to 678 bytes, which is just 3.4‰ of the original size. Notice that already the first compression rate reduces file size to 1.8kB, i.e. 1% of its original size.

Danny
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Joined: Sat Sep 04, 2004 5:09 pm

Post by Danny » Tue May 27, 2008 11:17 pm

Yeah, it doesn't really make sense since the program should find out by itself which level to choose for best results.

Just crank it up to max and never look back i'd say.
Get the bugs fixed, THEN start adding features. It sucks, but someone has to do it.

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