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Colors Common Block? [message #12540] Thu, 20 August 1998 00:00 Go to next message
dirk is currently offline  dirk
Messages: 15
Registered: March 1998
Junior Member
A question about color tables:

I want a simple inverted black and white color table, and i define it
with red, green, and blue arrays that all run from 255 to 0. Then i load
them in with

tvlct,red,green,blue

No problem. BUT, now I want to play with the stretch and gamma correction
for this new color table just like with xloadct.

The functions gamma_ct and stretch seem to be designed for this, but they
always remove my color table and re-establish the old black and white.
Adding the /Current keyword doesn't help.

The /current keyword is described as:
Set this keyword to apply correction from the "current" color table (i.e.,
the values R_CURR, G_CURR, and B_CURR in the COLORS common block).
Otherwise, correction is applied from the "original" color table (i.e.,
the values R_ORIG, G_ORIG, and B_ORIG in the COLORS common block). The
gamma corrected color table is always saved in the "current" table
(R_CURR, G_CURR, B_CURR) and the new table is loaded.

So I have a feeling that i need to somehow edit this Colors common block
so it has my tvlct values in R_Curr, G_CURR, and B_CURR.


Can anyone help before i resort to (shudder) IRAF?

Thanks!
- Dirk
Re: Colors Common Block? [message #12608 is a reply to message #12540] Mon, 24 August 1998 00:00 Go to previous message
David Foster is currently offline  David Foster
Messages: 341
Registered: January 1996
Senior Member
Dirk Fabian wrote:
>
> A question about color tables:
>
> I want a simple inverted black and white color table, and i define it
> with red, green, and blue arrays that all run from 255 to 0. Then i load
> them in with
>
> tvlct,red,green,blue
>
> No problem. BUT, now I want to play with the stretch and gamma correction
> for this new color table just like with xloadct.
>
> The functions gamma_ct and stretch seem to be designed for this, but they
> always remove my color table and re-establish the old black and white.
> Adding the /Current keyword doesn't help.

Dirk -

Welcome to the weird and wacky world of the COLORS common block!
Seems like a strange implementation to me, IMHO.

Try defining this common block in your code (at the level of your
stretch() call) and define the first 3 variables in this block:

common colors cr, cg, cb, curr, curg, curb
.
.
.
r=reverse(indgen(255))
g=r
b=r
tvlct, r,g,b
cr = r
cg = g
cb = b

; Now stretch() should use your "current" color-table!

Hope this helps.

Dave
--

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~
David S. Foster Univ. of California, San Diego
Programmer/Analyst Brain Image Analysis Laboratory
foster@bial1.ucsd.edu Department of Psychiatry
(619) 622-5892 8950 Via La Jolla Drive, Suite 2240
La Jolla, CA 92037
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~
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