Add transparency to colormap

Hi,

How can I add transparency to a colormap 2D?

I have the following code and I am using the version R2016a of MATLAB.

function covFunc( mapa, minPrx, maxPrx, arrayPrx )

wallMask(:,:,1) = mapa.img(:,:,1) ~= 255 & mapa.img(:,:,2) ~= 255 & mapa.img(:,:,3) ~= 255;
cover = (arrayPrx') .* ~wallMask + wallMask.*minPrx; 
cover = cover + 0 * wallMask;
cover = (arrayPrx') .* wallMask;
imshow(cover);
caxis([minPrx maxPrx])  % Set colormap limits
colormap (jet(round((maxPrx-minPrx/50))))
colorbar

end

I need that the image stays intact and the new colors created by the color map stay transparent.

Answer 1

[Image Analyst]

I'd probably create a new RGB image with the colormap and ind2rgb(). Then take a weighted average of them

rgbImage = cat(3, grayImage, grayImage, grayImage);
rgbOverlay = ind2rgb(grayImage, cmap);
factor = 0.6; % 60% or whatever.
rbgOutput = uint8(factor * double(rgbImage) + (1-factor) * 255 * rg0bOverlay);

[Oliver Lestrange]

I am sorry, I'm not understanding.

The variable grayImage is the return of the imshow function, right?

Is this what you are suggesting?

function covFunc( mapa, minPrx, maxPrx, arrayPrx )

wallMask(:,:,1) = mapa.img(:,:,1) ~= 255 & mapa.img(:,:,2) ~= 255 & mapa.img(:,:,3) ~= 255;
cover = (arrayPrx') .* ~wallMask + wallMask.*minPrx; 
cover = cover + 0 * wallMask;
cover = (arrayPrx') .* wallMask;
im = imshow(cover);
caxis([minPrx maxPrx])  % Set colormap limits
cmap = colormap (jet(round((maxPrx-minPrx/50))))
rgbImage = cat(3, im, im, im);
rgbOverlay = ind2rgb(im, cmap);
factor = 0.6; % 60% or whatever.
rbgOutput = uint8(factor * double(rgbImage) + (1-factor) * double(rgbOverlay));
colorbar

end

[Image Analyst]

No, it's the output of imread(). Try this:

grayImage = imread('moon.tif');
rgbImage = cat(3, grayImage, grayImage, grayImage);
cmap = jet(256);
rgbOverlay = ind2rgb(grayImage, cmap);
factor = 0.6; % 60% or whatever.
rgbOutput = uint8(factor * double(rgbImage) + (1-factor) * 255 * rgbOverlay);
% Show everything
subplot(2, 2, 1);
imshow(grayImage);
title('Original Gray Scale Image');
subplot(2, 2, 2);
imshow(rgbOverlay);
title('Colormapped Image');
subplot(2, 2, 3);
imshow(rgbOutput);
title('Blended Image');

Once you have an RGB image, you wouldn't use a color bar - that's used only for indexed images.

[Oliver Lestrange]

In my code the ind2rgb returns error.

Assignment has more non-singleton rhs dimensions than non-singleton subscripts

Error in ind2rgb (line 34)
  rout(:,:,1) = r;

I am using:

cmap = jet((round((maxPrx-minPrx/50))));
rgbOverlay = ind2rgb(mapa.img, cmap)

Where mapa.img is the image.

I don't understand very well image processing... but cmap is getting a 14x3 matrix and the image is a 15x15x3. I don't know if that can be a problem...

But I think the matter here is that the values of maxPrx and minPrx are negative.

Any suggestion?

Thanks for the demonstration above.

[Image Analyst]

You forgot to attach your script and your image. So, how can I help? cmap can be as many colors as you want to quantize it into. I have no idea what your maxPrx and minPrx are.