RE: GIFs vs JPEGs

Perhaps a brief explanation of how jpeg works would help
here. JPEG breaks the image up into cells which I seem to
recall are 8x8 pixels. The image in a given cell is 
represented as a series of mathematical expressions where
the coefficients are stored in the jpeg file. There are
other steps in the compression process, but these coefficients
are where the actual compression, and artifacts, are
controlled. The higher the compression, the more of these
coefficients are truncated. If they are not altered at
all, then the image is lossless, but if there is extreme
compression, then the artifacts become objectionable, and
the images from cel to cel don't even match, giving a
blocky appearance. This leads to variations, pixel to
pixel, even in areas like solid white backgrounds, and
even with modest compression ratios. If you don't need the
larger color palette,then GIF is better, but for  photo
images, jpeg is normally necessary. With photographic
images, these artifacts are normally not noticed at 
normal compression ratios.

The bottom line is that all the above doesn't really help
in the stated problem, but may help to understand the
compromise that has to be accepted. If you need jpeg, then
one has to figure out the proper compression ratio to
get the best compromise between file size and image quality.

Gary


> -----Original Message-----
> From: owner-hwg-basics(at)hwg.org [mailto:owner-hwg-basics(at)hwg.org]On
> Behalf Of Mike Eovino
> Sent: Wednesday, October 06, 1999 7:10 AM
> To: Sharon Elix; hwg-basics(at)hwg.org
> Subject: Re: GIFs vs JPEGs
> 
> 
> Sharon,
> 
> I don't know what others have found, but I've found that a solid field of
> white in a JPEG tends to come out looking a little pink.  I don't 
> know why,
> but I think it may have something to do with JPEG's compression algorithm
> changing colors.  GIF's tend not to change color.  May explain 
> spottiness as
> well.
> 
> 

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