colormap/caxis edit roipoly

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

[Image Analyst]

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;

[William]

Fantastic, thanks :)

Answer 2

[Charlotte Chaze]

The previously accepted answer doesn't work for me in R2017b - here is what does, using OP's example img.

When you use roipoly, it resets caxis to [0 1]. So just change the scale in your img to [0 1]. In this case, here are the series of commands you'd use:

Use 'caxis' to find out what the scale of your image is.

caxis

Say it's [0 1000]. This will give back

ans = [0 1000]

Now, divide your img by 1000 to reduce the caxis to [0 1]. Then use roipoly on that.

img = img ./ 1000
mask = roipoly(img)