transparent background for scatter plot

Hi,

I am presenting an image using imagesc, and I want to draw a scatter plot on top of the figure, without changing the background, and without it auto-scaling.

for example:

a = rand(100,200); % the image to be presented...
imagesc(a)
hold on
scatter(1:100,1:100,30,1:100,'filled')
hold off

if you run the code, you can see that when the scatter is being ploted, the image (a) is changed. how can I prevent that (and keep the same colormap for the scatter points)?

Thanks!

Answer 1

[OCDER]

imagesc will use the colormap of the figure, so if you want to use a different color scheme for scatter, calculate out the rgb values to use. See the sample code to see how 2 color schemes can be used:

A = rand(100,200); % the image to be presented...
HotClr = hot;   %Mx3 rgb matrix for hot color scheme  (for imagesc)
CoolClr = cool; %Mx3 rgb matrix for cool color scheme (for scatter)

imagesc(A) %will autoscale image according to FIGURE's ColorMap
colormap(gcf, HotClr); %setting figure colormap to hot color scheme
hold on
CoolIdx = ceil(linspace(1, size(CoolClr, 1), 100)); %find index of the different color map
scatter(1:100,1:100,30,CoolClr(CoolIdx,:),'filled'); %use the RGB values per dot instead of figure colormap index.
hold off