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From: "Prasanna " <pmgunawardana@gmail.com>
Newsgroups: comp.soft-sys.matlab
Subject: Re: How to extract yellow color under different iluminations
Date: Tue, 20 Oct 2009 08:33:02 +0000 (UTC)
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Thank u very much for your immediate reply.I am going to identify the traffic sign (.jpg) image. And it is rectangular shape sign image, no border. back ground of the sign is yellow.middle of the sign contain the "left bend" sign with black color. I have taken the several pictures of that under different light conditions. I want extract the yellow color area and do some further analysis. Unfortunately I don't have the pictures right now. I will send them bit later. Until that if you get a rough idea please share it with me.

Regards
Prasanna.

"John D'Errico" <woodchips@rochester.rr.com> wrote in message <hbhira$906$1@fred.mathworks.com>...
> "Prasanna " <pmgunawardana@gmail.com> wrote in message <hbhgam$3ok$1@fred.mathworks.com>...
> > Hi,
> > 
> > How can I extract the yellow color regions from a .Jpg file under different illumination conditions? Please help me with this. Send me the codes or the method.
> > 
> 
> The "yellow" color region alone of color space is
> non-simple to describe, that will depend on the
> color space you might work in. A blob is the best
> description.
> 
> Now, you want to change some nominal illuminant,
> then to recover from the original scene or from a
> print, which pixels fall into that nondescript blob?
> This is a non-simple problem, made worse because
> of your less than complete description of the
> problem. Which illuminant must be changed? That
> of the original scene? That of the environment in
> which we will view a print, or the monitor? Or
> maybe change the monitor white-point? Any of
> these can be difficult problems to solve, depending
> on how well you wish to do the job.
> 
> For example, if it is a question of print viewing, then
> we need an accurate characterization of the printer.
> We will need to know the device gamut for how this
> device prints yellows. Which pixels were out of gamut,
> and exactly what strategy is used to move those
> colors to the device gamut. (There is more than one
> such strategy to be found.) Alternatively, you need
> a mapping that will predict where each color in
> the original color space ends up after it is printed.
> Finally, we will need to have a good specification of
> the region of a color space where the color yellow
> lives.
> 
> Sp yeah, right, we'll get right on it. Stop work on
> all else and send you code for this immediately.
> If you really expect an answer, then it will at most
> be in the form of some ideas on what to do. Even
> for that, you MUST give an adequate description
> of the problem you are trying to solve.
> 
> John