Re: tvrd and device,decomposed=0

["Liam Gumley" <Liam.Gumley(at)ssec.wisc.edu>]

David Fanning <davidf@dfanning.com> wrote in message
> All this monkeying around with Device Decomposed is a hassle,
> of course, but that is why I wrote TVIMAGE and Liam wrote IMDISP,
> so you don't have to worry about it. I frankly don't know why
> RSI doesn't offer to buy this code from either one of us.
> (Well, I can guess why they don't buy it from me, but what
> has Liam ever done to make them upset?) :-)

It's too late for me to make any money from IMDISP, what with the GNU GPL
and all. Still it's nice to have intelligent people tell me they learned
something from reading the code:
http://cimss.ssec.wisc.edu/~gumley/imdisp.html

R. Bauer wrote
> > Why are the results of tvrd and tvlct not itself changed automaticly
> > to pseudo_color?

TVRD is a very low level function, and it needs a fair bit of intelligence
wrapped around it to get sensible results, such as the SAVEIMAGE screen
grabber:
http://cimss.ssec.wisc.edu/~gumley/imagetools.html

If you display a PseudoColor image when IDL is running in 24-bit mode, and
you read the screen using TVRD into a TrueColor image array, there is no
guarantee that you can convert the array to a PseudoColor image (using
COLOR_QUAN or anything else) that would *exactly* match a PseudoColor image
which was displayed and read from the screen in 8-bit mode.

I run in 24-bit all the time, and I've given up saving 8-bit images from the
screen for this reason. I save TIFF images if I want lossless compression,
or JPEG images if I don't mind lossy compression.

Another reason to avoid a certain well-known 8-bit image format is the
licensing issues which are involved:
http://burnallgifs.org/

Cheers,
Liam.