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Re: transparent GIF pixels

On 10 Aug 2000, Craig Markwardt wrote:
>davidf@dfanning.com (David Fanning) writes:
>> Craig Markwardt (craigmnet@cow.physics.wisc.edu) writes:
>> > David, I think he's talking specifically about GIF transparent pixels.
>> > I understand that you can reserve one GIF color to be transparent, so
>> > to speak.  Any pixels with that color are not rendered, so any
>> > background graphics can show through.  This can be especially useful
>> > in web programming.  I don't think he's actually trying to render it
>> > on the screen himself.
>> I'm not so sure. But I admit "I would like to make them transparent
>> while the image is in memory." could be open to interpretation.
>> I thought he wanted to see transparent pixels in IDL. Why else would
>> he be saving and reading them back?
>I think he said he wanted to *avoid* writing and then reading back.
>Other than that let's keep agreeing.

I'm using ION to make images for a website. ION is "IDL On [the] Net"

For those of you who know html, its really as simple as this to generate

   ;;; idl code goes here

and *wow*, you have a gif or jpeg _inside_ your web page that is generated
based upon inputs supplied to the page by the user.

But, yes, GIF's can have pixels that are transparent in that they show the
background through them. WRITE_PNG has a transparent option, so i could
write a PNG with transparent pixels, then re-read it the NEXT command
(this stupid and slow), and then display that image to the page, and have
my transparent (see-through) pixels.

But i would prefer to do all that in memory, rather than using the
webserver to needlessly read/write to PNG image.