comp.lang.idl-pvwave archive: archive

Home » Public Forums » archive » Re: gamma correction

Show: Today's Messages :: Show Polls :: Message Navigator
E-mail to friend

Re: gamma correction [message #31231 is a reply to message #31230]

Thu, 27 June 2002 16:57

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Dick Jackson (dick@d-jackson.com) writes:

> But if you just want to try adding a 'gamma correction' (an exponential
> function) in IDL as a step in the middle (between the camera and the monitor), I
> see no harm in using Gamma_CT as in my example. I would just keep in mind that
> there is already some function going on between the image array values and the
> light coming from the monitor (something close to a gamma function at around
> gamma=2.5 as Rick mentions). By changing the colortables with Gamma_CT or just
> using TVLCT, you are just adding another function in front of that.

I just point out again that while this would probably
work on a Mac and PC, it probably won't work on a
UNIX machine. The last time I checked (several years
ago and God knows RSI has changed the way color works
enough times that two years is ancient history), a
UNIX machine in TRUECOLOR mode, with color decomposition
turned OFF, did not take the image values through the
color table before display, as it does with PCs.

In other words, on UNIX machines a true-color image
is a true-color image and what you have is what you
see. I always thought this was the correct way to
operate and assumed the PC behavior (which almost
always results in wacky image colors) was a bug.

Now I see that the fore-sighted engineers at RSI
were really concerned about gamma correction and
had put the machinery in place to handle this
without me even realizing it. Have I mentioned that
I *love* IDL! I'm just feeling sorry for the UNIX
guys now. They are going to have to modify the
numbers in their image to get the same effect.

> Sorry for the long ramble, I hope it's of some help.

I think the long discussion just points out my
earlier contention that gamma is a strange thing
and it is hardly ever clear what you mean by it.
Charles Poynton is clear about most things having
to do with color, and in my experience almost
invariably right. I look forward to seeing the IDL
code that results. :-)

Cheers,

David

--
David W. Fanning, Ph.D.
Fanning Software Consulting, Inc.
Phone: 970-221-0438, E-mail: david@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155

Report message to a moderator

[Message index]

		Re: gamma correction By: David Fanning on Fri, 28 June 2002 07:29
		Re: gamma correction By: Craig Markwardt on Fri, 28 June 2002 06:33
		Re: gamma correction By: Dick Jackson on Thu, 27 June 2002 21:42
		Re: gamma correction By: Med Bennett on Thu, 27 June 2002 20:53
		Re: gamma correction By: David Fanning on Thu, 27 June 2002 16:57
		Re: gamma correction By: Dick Jackson on Thu, 27 June 2002 16:14
		Re: gamma correction By: David Fanning on Thu, 27 June 2002 13:23
		Re: gamma correction By: btupper on Thu, 27 June 2002 12:34
		Re: gamma correction By: Rick Towler on Thu, 27 June 2002 11:06
		Re: gamma correction By: David Fanning on Wed, 26 June 2002 15:22
		Re: gamma correction By: David Fanning on Wed, 26 June 2002 15:20
		Re: gamma correction By: Dick Jackson on Wed, 26 June 2002 14:17
		Re: gamma correction By: David Fanning on Wed, 26 June 2002 12:11
		Re: gamma correction By: Med Bennett on Wed, 26 June 2002 11:27
		Re: gamma correction By: David Fanning on Wed, 26 June 2002 07:44
		Re: gamma correction By: Craig Markwardt on Fri, 28 June 2002 14:01

Previous Topic:	Re: Delvar?
Next Topic:	Delvar?

-=] Back to Top [=-

[ Syndicate this forum (XML) ] [

] [

]

Current Time: Sun Oct 12 14:35:02 PDT 2025

Total time taken to generate the page: 2.13584 seconds