Remove image outside of Contour Plot

The following code gives the attached image.

figure, imshow(NT,'DisplayRange',[]);
hold on
MNSContourThreshold = 0.5*double(MaxNonSpecific)
contour(NT,[MNSContourThreshold MNSContourThreshold], 'color', 'g')

I now want to set every pixel (within the brain image) on the outside of the contour line to 1 (Black).

Answer 1

[Image Analyst]

What exactly does that mean? You mean you want a 1-D list of all pixel values outside one of the contour lines? The contour line at which level? Then do this:

mask = NT < someValue;  % or >
pixelValues = NT(mask);  % A 1-D list of all pixels below someValue.

Or do you want to mask the image, like you want a 2-D image but want the inside of the contour blackened or set to some other value like 1 or 255 or inf or nan? Like

NT(mask) = someValue; % For example NT(mask) = 0;

[Harry Andrews]

[edited question to reflect this] Thank you for helping! Sorry, I should've been clearer.

The following code gives the attached image.

figure, imshow(NT,'DisplayRange',[]);
hold on
MNSContourThreshold = 0.5*double(MaxNonSpecific)
contour(NT,[MNSContourThreshold MNSContourThreshold], 'color', 'g')

I now want to set every pixel (within the brain image) on the outside of the contour line to 1 (Black).

[Image Analyst]

Did you try what I said?

mask = NT < MNSContourThreshold;
NT(mask) = 1; % Set to almost black.

If not, why not?

[Harry Andrews]

Ah you hero, sorted!!! Thank You ❤