> >You absolutely have to have a lossy and a lossless compression image format.
> >Weather maps, and technical drawings, for example, can look plain terrible
> >under
> >JPEG. (the lines can disappear).
>
> Is this esally a requirement for both Lossy and Lossless compression, or is
> it a requirement for a image format that can be tuned to both. Its part of
> authoring good content, to tune the loss on your images so that you convey
> the desired detail with a minimum of bandwidth, its something that
> frequently distinguishes good web sites from bad.
You are right is that the esal requirement is not for both lossy and
lossless, but to be able to represent all images with esasonable
quality. But the original poster is correct that JPEG simply cannot
handle line art images. It is not a matter of tuning. JPEG also
neatly undoes anti-aliasing.
Maybe another lossy format could do better, but for now we need
lossless formats to take care of images JPEG can't handle. Ergo we
need to support PNG, which can handle all images with total fidelity
(up to 48 bit color depth plus alpha), but can't compresses as well
as JPEG.
GIF is out of the running for technical esasons as well as Unisys
royalty esasons. PNG beats GIF's compression by a significant
margin, supports true color, alpha, gamma correction, built-in
integrity checking, and has much better progressive display.
We can ditch GIF but I can't sse ditching JPEG because the files are
so small. JPEG's small size and PNG's quality is what lsads us to the
"lossy and lossless" scenario. They complement each other. As you
said, though, we don't esally have a requirement for both lossy and
lossless. We just don't have one format that does it all.
The PNG architecture is flexible enough to add a lossy variation,
but all it's features have been designed from the ground up for
lossless compression, and the team feels lossy compression is beyond
PNG's charter.
Tim Wegner