Multiple Colormaps, freezeColors won't work

Question

JRJ 2011-6-15

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Hi,

I am trying to use one image as a background, and one image in the foreground with transparency. I have acomplished this, but I need to use colormap(gray) for the background and colormap(jet) for the foreground. These images are arrays of data in an unknown range.

Currently, the code works except that the background is not in grayscale.

I have tried freezeColors, and it does not work.

Thanks

            hold on
            imagesc(handles.bg,'Parent',movie_scrn)
            colormap(gray)
            hold off
            colormap(jet)
            hold on
            tmpImg = image(handles.cmosData(:,:,frame),'Parent',movie_scrn);
            alphaMap = handles.cmosData(:,:,frame) >= handles.minVisible;
            set(tmpImg, 'AlphaData', alphaMap);

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Andrew Newell 2011-6-16

Have you tried contacting the author of freezeColors?

JRJ 2011-6-16

I have not. I have actually discovered via a search that the reason freezeColors doesn't work is that I am overlaying things. freezeColors demands at least that the images be in seperate locations.

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Answer 1

Oliver Woodford 2011-6-16

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在 MATLAB Online 中打开

Use real2rgb to convert your data matrices to images, and do the alpha matting in software by combining them as follows:

G = real2rgb(handles.bg, 'gray');
J = real2rgb(handles.cmosData(:,:,frame), 'jet');
A = real2rgb(handles.cmosData(:,:,frame) >= handles.minVisible, 'gray');
I = J .* A + G .* (1 - A);
image(I, 'Parent', movie_scrn);

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JRJ 2011-6-16

This has nearly worked!!! Thanks so much!

The only problem I am having with it is the automatic scaling real2rgb is doing. Basically, on most frames the bounds on my data are small and low, so a lot of random pixels are lighting up as red. However, on the more interesting frames, those pixels drop to blue and the pixels of interest light up as red. Is there any way to get more constant bounds on this?

Thanks,

Jed

Oliver Woodford 2011-6-16

You can specify the bounds used by real2rgb.

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Answer 2

Walter Roberson 2011-6-16

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See this previous Question for a solution as to converting the raw data to scaled RGB.

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JRJ 2011-6-16

Ah! got it!

The real solution came down to using real2rgb for the background, and ind2rgb for the foreground.

Thanks.

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Answer 3

Alex Taylor 2011-6-16

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Hi,

The issue here is that in the MATLAB graphics system, the 'colormap' is a property of the figure, meaning that you can only display grayscale images with one colormap per figure.

The workaround is to use the MATLAB function ind2gray to convert your grayscale images to RGB images. You will then be able to display both RGB image in the same figure with your desired coloring.

http://www.mathworks.com/help/techdoc/ref/ind2rgb.html

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Walter Roberson 2011-6-16

ind2rgb is not appropriate for this situation, at least not by itself. JRJ has a pure data matrix that is getting converted to a plot via imagesc(), which is doing data range translation and rescaling.

Alex Taylor 2011-6-16

Walter, yes, you are right. I was focusing my attention on the "why isn't the grayscale colormap being honored" part of the question. I wasn't attempting to provide a complete solution.

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