MATLAB: Colormap/caxis edit roipoly

Question

I would really appreciate help on this one,

Using roipoly to isolate data but when the function displays the initial image I want to draw on, the scaling is all wrong and it just shows a black image.

Applying colormap or caxis on figure editor shows the scaling is wrong but the below code does nothing. How can I set caxis on roipoly figure?

e.g.

BW = roipoly(img)
colormap hot
caxis([0 1000])

Many thanks, Will

Answer 1

Don't pass in img - I never do. Just set up the image in advance as far as how you want it to look.

imshow(img, []);
colormap(hot(256));
colorbar;
mask = roipoly;