Hi John,

John Culleton wrote:
> I wonder how 
> many of her cautions are universal and how many just 
> dependent on the program used to create the graphics?

Her comments on web graphics are, IMHO, universal, as opposed 
to limited to one program or another.

> Even if a person simply cannot create clean edges (one of 
> the most common mistakes is using "tansparent" on a layer - 
> transparent doesn't work..you  need to use the background 
> colour as the background colour on the image around any 
> curved lines. Also that "delete" background rarely gives a 
> clean lift - that all needs to be erased one pixel at a 
> time.) they can go with text only, or visit one of the 
> 1000s of sites that offer free web tools, or avoid curved 
> edges (in most cases jaggies are only an issue around 
> curved edges).

This is a fair comment. Transparency (in GIF, and as supported by
IE in indexed PNGs) is limited to one palette entry which is
completely transparent, and the rest completely opaque. Usually,
smooth rounded edges are obtained by antialiasing the curve,
going in grades from opaque to transparent over a number of
pixels. Since you can't antialias to transparent in gif,
round edges usually look crap. However, if you have a background
that isn't transparent, then you can antialias from white to
green, say, just fine, and have some of that smoothness kept
across an indexing operation.

However, PNG supports indexing much more advanced than that -
essentially, an indexed palette entry in png has an alpha
component, so with indexed png you can antialias to transparent.
However, this isn't supported in IE for Windows. You can also use
32 bit PNG which is funny supported on both IE and Mozilla, but
is a much larger file size.


       David Neary,
       Lyon, France
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