Comments on: All about pixel colors: Scaled indexed images

By: Steve

Steve — Mon, 28 Nov 2011 17:06:22 +0000

Stephan—No, there’s nothing like that. I would love to see a more general data-to-color mapping capability available in MATLAB for image display. I’ll mention it to the graphics team.

By: Stephan

Stephan — Thu, 24 Nov 2011 13:24:45 +0000

Hi Steve,

when using imagesc, the data is mapped LINEARLY to the colors of the colormap. Is there a way to change the mapping function to e.g. a logarithmic one?
(I mean, alternatively I could modify the data and then also modify the tick labels on the colorbar accordingly… but changing the mapping function would be much more elegant.)

Thanks,
Stephan.

By: Steve

Steve — Wed, 05 Jan 2011 16:36:34 +0000

Marco—I think that imagesc just ignores nonfinite values when computing the range.

By: marco peralla

marco peralla — Thu, 16 Dec 2010 15:16:49 +0000

I wonder how these linear re-scalings work in the case that you have -Inf for example. More precisly when i plot log intensity map of a magnitude spectrogram of a sound (so that the components with zero intensity turn to -Inf) when i do imagesc it shows an acceptable map however if I tend to save that log-intensity matrix to a image or ascii file my self i fail, i need to know how imagesc copes with these situations. can you help me with that ?

thanks

By: Steve

Steve — Fri, 24 Jul 2009 00:48:37 +0000

Ilan—Try my imoverview function on the MATLAB Central File Exchange. Compute the mask using something like this:

bw = abs(A - 1.2) <= tolerance;

By: Ilan

Ilan — Wed, 22 Jul 2009 07:12:16 +0000

Hi Steve,

I have a gray image (values ranging from 0 to 5) and I want to color pixels which have certain value (say 1.2).

How can I do that?

Hope you can help.

Thanks,

Ilan

By: Steve

Steve — Fri, 19 Sep 2008 11:39:21 +0000

Greg—I don’t understand your question. Which pixels? Highlight them how? And how is highlighting related to getting the average?

By: Greg

Greg — Fri, 19 Sep 2008 03:55:51 +0000

Now what if you wanted take that original imagesc(A) and highlight a few differnt pixels to get the average related to the original array [A]? Thanks!

By: Steve

Steve — Wed, 16 Apr 2008 17:42:32 +0000

Alex—The default colormap length returned by hot has only 64 colors, so it doesn't make sense to use it to display a 16-bit image with values that go from 0 to 1500. When I try that, I get an image that's all white, which is what I would expect. You might have better luck with something like this:

% Display using the autoscaling syntax of imshow
imshow(I, [])

% Crop
[ROI,rect] = imcrop;

By: Alex

Alex — Wed, 02 Apr 2008 19:27:35 +0000

Dear Steve,
Why am I having trouble using the imcrop function with a scaled image? Or, rather, why does the image not appear scaled anymore when I try to do imcrop on it? I have 16bit TIFF files with values that go from 0 to like 1500. I can use the imagesc function to display them just fine. But what I want to do then is to create regions of interest on such a scaled image. I was trying to use imcrop, but as soon as I put in [ROI,rect] = imcrop(I,hot); the scaled image that was on the screen is replaced by a solid black rectangle. Why is this, and how do I make it work how I want?
Thank you if you can help!