how to convert an image to topography image?

I have a 2D C.T image. I would like (in some way) to calculate roughness of the image. I need to translate each pixel to its height and later to calculate the variance. It's important to mention that I don't have the height information for each pixel.

[Walter Roberson]

What does the intensity value of each pixel correspond to?

Answer 1

[Sean de Wolski]

To calculate the variance, take the square of the output of stdfilt

doc stdfilt