On Sun, Nov 11, 2001 at 11:12:56PM -0500, Erik Mooney wrote:
> 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.
Or cartoons, or all sorts of low-color things. But anyway, the compression
_is_ lossless, the format just supports only paletted images. But there's
no data loss from compressing, decompressing, and recompressing a
suitable image.
> IIRC, LZW isn't the patented part of GIF; the whole file format is
> Compuserve's proprietary intellectual property. LZW is openly available.
No, LZW is Unisys's property, IIRC. They sued CIS.
> There is no good true lossless compression for photographic images. Any
> format will result in a huge file.
Actually, there are some nice (although patented) extensions to JPEG
for lossless encoding of truecolor images which are supposed to be
pretty good.
--
-/
|/| Julian Squires <tek@xxxxxxx>
/-
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