Segmenting an image according a threshold

Say that I have a grayscale image, which values range from `[0,255]`. Say that I want the pixels which values are larger than or equal to `66` for instance to be `white`, and the rest pixels to be `black`. How can I do that in `MATLAB`?

Thanks.

Answer 1

[Image Analyst]

The easiest way by far, is to simply threshold:

binaryImage = grayImage >= 66;

Ashish's method doesn't create black pixels, and Kevin's is inefficient. My fast and efficient method will create a binary image which is used in virtually all processing afterwards, such as labeling, morphology, regionprops, hole filling, etc.

Answer 2

[Kevin Claytor]

thresh = 66;
I(I < thresh) = 0;
I(I > thresh) = 255;

[Ashish Uthama]

[Edit, I meant to correct Kevin's code, pointing out the need for >=]

I(I >= thresh) = 255;