ALPHAMASK: semi-transparent image overlay

ALPHAMASK: Overlay image with semi-transparent mask

Overlays a semi-transparent mask over an image. By default the
currently displayed figure is overlain.
Options include overlay colour and opacity.
Returns a handle to the overlay mask.

Usage:
hOVM = alphaMask(bwMask, [colour, transparency, axHandle])
bwMask: logical matrix representing mask
colour: vector of three rgb values in range [0, 1] (optional; default [0 0 1])
transparency: scalar in range [0, 1] representing overlay opacity (optional; default 0.6)
axHandle: handle to axes on which to operate (optional; default current axes)
hOVM: handle to overlay image is returned

Example:
figure;
I = peaks(200);
bwMask = eye(200);
imshow(I, [], 'Colormap', hot);
alphamask(bwMask, [0 0 1], 0.5);

See also IMSHOW, CREATEMASK