extract only white pixels from an image

How can I extract mean and variance of only white pixels of an image?

Answer 1

[Image Analyst]

What value do you consider "white"? Let's say it's 230. Then you can get a binary image

binaryImage = grayImage >= 230;

Now, exactly what does "extract" mean to you? You want to consider all the gray values in the binary image? If so do

maskMean = mean(grayImage(binaryImage));
maskSD = std(grayImage(binaryImage));
maskVar = var(grayImage(binaryImage));

[Mary Baratzadeh]

excuse me, my mean is calculate the average white pixels of an image