Identifying only specific areas of image above a certain "threshold"

Now, here is an color image which i am converting it into grayscale inorder to identify only white bands that are above some threshold and represent the starting positions(column) of those white bands. How do i decide the threshold ? Also, is it possible to convert the image into black and white and then identify the white bands by putting a threshold condition ?

Answer 1

[Image Analyst]

You can look at the histogram with imhist(). Then choose a threshold. Or you could use my thresholding app: http://www.mathworks.com/matlabcentral/fileexchange/29372-thresholding-an-image

Then you can segment your image, like shown in my Image Segmentation Tutorial: http://www.mathworks.com/matlabcentral/fileexchange/?term=authorid%3A31862