Scatter overlay on image with MATLAB - matlab

Question

I have an RGB image, img, and I want to produce a new image, img2, with an overlay scatter plot on it.
If X Y Z are respectively the nx1 vectors of x-coord, y-coord and "magnitude" value of my scatter what I'm doing is:
imshow(img);
hold on;
scatter(X,Y,3,Z,'fill');
hold off;
In this way I actually get an image with the scatter plotted, but the problem is that every point of the scatter has the same color (blu) instead of what normally happens when I use
figure;
scatter(X,Y,3,Z,'fill');
Any suggestions? Thanks.

Answer 1

Try to add figure; before imshow(), which will enables you to draw on the image with the color that what normally it should be.
figure; % add this line before imshow()
imshow(img);
hold on;
scatter(X,Y,3,Z,'fill');
hold off;
Here is an example I just tested:
figure; % add this line before imshow()
imshow(img);
hold on;
load seamount
s = sqrt(-z/2);
c = z;
scatter(x,y,s,c,'fill')
hold off;
You can see that its color shown on the image is (roughly) consistent with the color when drawing it alone.
Edit: you can always change the color to whatever you like by setting scatter's color properties, i.e. MarkerEdgeColor and MarkerFaceColor.

Answer 2

Ok, remapping the values of Z to 0-255 it works fine. Here is my function to do that:
function [ Aremaped ] = remap( A,lnew,hnew )
Aremaped = zeros(size(A));
lold=min(A);
hold=max(A);
for i=1:length(A)
newVal = lnew + (A(i)-lold)*(hnew-lnew)/(hold-lold);
Aremaped(i) = newVal
end
end
Hope this can help