Get the pixel-width of the vertical dark layers in grayscale image

Hi!

I have a grayscale image with dark and light vertical layers. I want to know the pixel-width of every dark layer in the image.

What I found problematic is that the image also contains noise which edge detection also finds. Another thing is that the dark layers differs in intensity values from each other.

Any sugestions which method can be used in this case?

Thanks in advance