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PNG compared to JPEG and GIF

I've used GIF and JPEG for ages now, and begin to discover PNG. I hear from many people it's better, and I know that transparancy is better in PNG - if supported by the browser of course.

Normally I use JPEG for photo's. If I use PNG (24 bits), the image size is much bigger, and I cannot specify a compression rate (using Photoshop 6). As an example I took a photo of 800 x 600 pixels. Saved as PNG it was 800kb, and the JPEG version varied between 100kb (for high quality or 60%) and 500kb (100% quality). So the best JPEG quality is half the size of the PNG. Why is PNG better?

If I save to PNG (version 1), then reopen the saved PNG (800 kb big), save that again as PNG (version 2), the size grows to 950kb. If I reopen the last PNG (v2) and save it again as PNG (version 3), it seems to keep the last size. Is this always the case? Is PNG 24-bits lossless? Or at least not incremental on losing information?

What do you prefer? JPEG or PNG?

How about GIF? I think I won't use it anymore. I've noticed PNG-8 has comparable file sizes. I never use animated GIFs, so I don't need that (and don't know if PNG supports animation). Do you have reasons to prefer GIF over PNG?
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grexx
Asked:
grexx
1 Solution
 
lherrouCommented:
Grexx,

First of all, remember that PNG was intended as a replacement for the GIF file format when Unisys said they would enforce the LZW compression patent, which was used in GIF. JPEG is still the primary lossy compression method for photographic or photographic-style images. PNG is not going to be the smallest format for photographic-type images in most cases. On the other hand, for a simple image, the GIF format, while called loss-less, in fact discards color information to achieve some of it's compression, and is limited to 256 colors or less (as set by user/software). PNG often, but not always, outperforms GIF on image quality and compression in images of these types.

The following article shows some excellent comparisons, and discusses when each should be used:
http://www.websitetemplatedesign.com/oscommerce_tutorials/printer_136.shtml

Cheers,
LHerrou
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