A subject may be interrogated with electromagnetic radiation for producing image data representative of an image of the subject. First and second image data, produced based on reflectivity in first and second frequency ranges, may be related. In some examples, image data for one picture element may be produced based at least in part on reflectivity of the radiation at a depth selected based at least in part on a depth of another picture element. In some examples, plural images may be produced based on reflectivity at different depths. In some examples, a value of reflectivity may be determined for an intermediate depth between two adjacent depths of image data based at least in part on reflectivity of the radiation for a plurality of spaced-apart depths.