Subject: Re: [stella] Homebrew-Homepage-Screenshots From: Erik Mooney <erik@xxxxxxxxxx> Date: Sun, 11 Nov 2001 23:12:56 -0500 |
On Sun, 11 Nov 2001 23:08:20 -0330, you wrote: >On Sun, Nov 11, 2001 at 09:07:48PM -0500, Erik J. Eid wrote: >> Albert Yarusso, one of the maintainers of AtariAge, told me that he prefers >> the "non-lossy" picture formats such as PCX, BMP, and PNG. I believe that >> GIF is a lossy compression format. > >GIF uses LZW compression, which is non-lossy. LZW is patented, however, >so you end up losing in a different way. PNG is a good alternative.[1] >Unfortunately PNG is not as widely supported as GIF. >(you're thinking of JPEG, which uses quantization and DCTs to aid >compression, both of which cause loss) Actually, GIF is in fact lossy! GIFs can only have a 256 color palette, so the image is first quantized lossily to 256 colors, then lossless LZW compression is applied. PNG is the same, except it uses a 16-bit palette. GIF _is_ lossless for images generated by computer, like diagrams or screenshots, that begin with 256 colors or less. That's its intended function. IIRC, LZW isn't the patented part of GIF; the whole file format is Compuserve's proprietary intellectual property. LZW is openly available. There is no good true lossless compression for photographic images. Any format will result in a huge file. ---------------------------------------------------------------------------------------------- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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