Re: How to do efficient overlay with IDL ?

[Craig Markwardt <craigmnet(at)cow.physics.wisc.edu>]

"Jean Luc MAILLART" <jeanluc.maillart@wanadoo.fr> writes:
...
> This kind of method is not very efficient under 256 colours, and is
> dramaticaly slow under full colors display, and limit the ability to deal
> with real-time processing (50 or 60 frames/sec).
> 
> Is somebody knows :
> 
> 1) Why IDL is dramaticaly slower in full colors (3 to 4 time more than in
> 256 colors !) ?
> 
> 2) Others more efficient methods to deal with overlays informations on IDL ?

Memory bandwidth is probably killing you.  It's not clear to me that
*any* program can do 50-60 frames/sec.  It depends on the image size,
which you don't say.  It takes time to transfer the bytes to the video
memory buffer, and that time may be too long for you.  You might want
to write a sample program in straight C to see the maximum bandwidth
you can achieve.  If there are color conversions then it will slow
down even more.

Wy is true color 3-4 times slower than 8-bit color?  My guess is that
it's transferring 3-4 times as much data (24 or 32 bits versus 8 bit).

Craig

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Craig B. Markwardt, Ph.D.         EMAIL:    craigmnet@cow.physics.wisc.edu
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