I have an image (png) that I want to put underneath a heatmap(so to speak) made from a and a 2D matrix of values 0-1. So the intensity of the spot would be decided by how large the value in the matrix is.
I can use imshow(matrix) but that completely draws over the image underneath. Is it possible to perhaps, not draw any pixels with matrix values <.05 or some other way to make this work?
Answer
Here is an example of overlaying a binary heatmap on top of a color image:
%# some image
I = im2double( imread('peppers.png') );
%# I create here a random mask (gaussian centered in middle of image)
[r,c,~] = size(I);
[X Y] = meshgrid(1:r,1:c);
Z = mvnpdf([X(:) Y(:)], [r c]./2, diag(15.*[r c]));
Z = (Z-min(Z(:)))./range(Z(:));
Z = reshape(Z',[c r])';
%# show image and mask separately
subplot(121), imshow(I)
subplot(122), imshow(Z)
%# show overlayed images
figure, imshow(I), hold on
hImg = imshow(Z); set(hImg, 'AlphaData', 0.6);
%# also we can specify a colormap
colormap hsv
