PNG stands for Portable Network Graphics. It is a relatively new, very carefully designed image storage format. POV-Ray now supports, and recommends, image storage to the PNG format. It is starting to appear more frequently on the Internet. But why do we need another picture format??
There are essentially two picture formats used on the web: GIF and JPEG.
GIF stands for Graphic Interchange Format. It is a good format, all in all. However, the compression algorithm used in it (LZW) is patented (UniSys), and protected, and licensing fees are supposed to be paid for its inclusion in software. In addition, GIF supports only palette or color mapped images, up to 256 colors.
JPEG (or JPG) stands for Joint Photographic Enthusiast Group - and that is exactly what that format is designed for. It compresses images wonderfully, and can even compress them down to nearly nothing at all. At a price. JPEG is a 'lossy' format, in that some information is lost during the compression, in exchange for smaller file size. If you examine a JPG image, particularly a highly compressed one, you can clearly see a 'blotchiness' that is caused by the method of compression. There is a new 'lossless' JPEG, but it's use and support are not widespread.
GIF has been considered the choice on the web for illustrations, and JPEG for detailed, 24-bit images.
Now on to PNG. I stated above that PNG is a well planned format. One of the clearest instances of this is that it stores images in up to 64 bits per pixel, 16 bits each for red, green, blue, and alpha channel (transparency). JPG is only 24 BPP (8 each r,g,b) while GIF is only a 256 color, palette-based format.
PNG achieves very good compression rates (comparable to 75% jpeg, or 25% data lost) with NO loss of information. It is copyrighted, but freely usable. It is based on the ZLib compression library, and both it and ZLib can be compiled in library (link or runtime) form for any computer platform. Amiga browsers are leading the pack with PNG: only some browsers support PNG yet, but ALL Amiga browsers support it, several built-in. I've managed to locate a listing of several plug-ins for non-Amiga browsers, which is part of the official PNG home page. (see below)
I have also been given permission by Cloanto Italia to present here their V43.3 PNG datatype which will allow any picture.datatype supporting Amiga program to read PNG images. I strongly urge you to get this if you do not already have it. Finally, I have written an AREXX loader module for Art Department Pro which allows it to read PNG. (But not save) Download it!
More Information on PNG is available at:
PNG is copyright Andreas Dilger and Guy Eric Schalnat, Group 42, inc.
ZLib is Copyright Jean-Loup Gailly and Mark Adler
GIF is (as of this writing) copyright Compuserve, inc. an H & R Block company (for now..)
LZW compression is Patented, which patent is held by Unisys corp.
JPG is copyright Joint Photographic Enthusiasts Group. (I believe...)