displays

[Klaus Banse <kbanse@eso.org>]

Dear Midas Users,


   the situation concerning Midas displays and different visual modes has
been well (and very exhaustively) summarized by Werner Becker.

Since the 97NOV release Midas supported also TrueColor mode (i.e. RGB with
8 bits per color) for devices which supported that mode. In that mode you
would use 3 images (one for R, for G and for B plane) to get a combined "real"
color image display. On most high res devices, like e.g. my NCD Xterminal,
the installed Xserver would offer also PseudoColor mode besides the RGB mode
(and in parallel, so that different applications could work with different
visuals). Thus, you could choose in Midas if you wanted to use PseudoColor
or TrueColor mode for your displays (param 5 in command INITIALIZE/DISPLAY).

Recently PCs got more and more powerful graphics cards.
Unfortunately, most Xservers for PCs do not offer different visuals at the
same time, it's either Pseudo or TrueColor. Thus, you have to stop the Xserver,
edit the setup file and then restart X, in order to run applications requiring 
different visual modes.
Therefore, we included the possiblity to emulate PseudoColor mode on top of
TrueColor which uses 24bit graphics. Naturally, with such a board you can also 
use the TrueColor mode in Midas if you wish so. 
Also, note, that true color is not always true color... 
In X there is the distinction of DirectColor and TrueColor visual for 24 bit 
graphics. With DirectColor you can manipulate the colors via a LUT, whereas in 
TrueColor you cannot change the colors youself, there's just one fixed system 
LUT (usually a ramp). With the command SHOW/DISPLAY you can see which visual 
is supported by the Xserver.

If we cannot modify the colors directly in X, the LUT handling is emulated in
Midas, which has one "interesting" side effect:

Midas> load/image lola
Midas> load/lut heat

will NOT show the image `lola' with the colors of LUT `heat' immediately, only
the color bar at the bottom changes, have to do again 
  
Midas> load/image lola

to see the effect  (same goes for ITTs).
This is implemented in our last patch 1.4 for the 98NOV Midas release. 

Please, note, that we still do not support 16 bit graphics! There, you have
to switch your server to 8bit PseudoColor mode. And in view of our severe
manpower shortage I don't see how we'll manage that in the near future. 
So, it's only with 24 bit graphics cards where you can profit from this patch.


Good luck,
Klaus Banse