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Re: gamma correction [message #31229 is a reply to message #31223]

Thu, 27 June 2002 21:42

Dick Jackson
Messages: 347
Registered: August 1998

Senior Member

"David Fanning" <david@dfanning.com> wrote in message
news:MPG.1785543b517ba7a498991a@news.frii.com...
> Dick Jackson (dick@d-jackson.com) writes:
>
>> By changing the colortables with Gamma_CT or just
>> using TVLCT [with 24-bit images]
>
> 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.

Sorry, you had mentioned that. Would someone confirm whether this is still the
case!

> In other words, on UNIX machines a true-color image
> is a true-color image [...]
>
> 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!

:-) Gotta wonder, was it intentional? Could they be reconciled?

> 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.

We can always just make three lookup arrays and use them 'manually' to give the
same effect, as in:

newImageRedChannel = redLookup[origImageRedChannel]

Or simpler, if all three channels are using the same transfer function (simple
gamma curve, for example), we could just make one 256-byte lookup table and
then:

TV, /True, gammaLookup[origImage]

Cheers,
--
-Dick

Dick Jackson / dick@d-jackson.com
D-Jackson Software Consulting / http://www.d-jackson.com
Calgary, Alberta, Canada / +1-403-242-7398 / Fax: 241-7392

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[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

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