Contrast Adjustment

Abstract

The goal of all the medical imaging methods is to record a signal with sufficient resolution in intensity, space, and possibly time, to enable a medical interpretation of tissue structure and function. The information of interest, contrast of some sort, should be recorded in the intensity data – in other words, there should be sufficient intensity resolution in the raw data to discriminate the contrast details we are interested in. For a simple X-ray image on film this would mean that we have not under or overexposed the image. If a digital image constructed from the raw data is to be interpreted visually by a human, then we want the contrast information to be easily visible. To achieve this we will usually have to adjust the contrast of the image. This can be done in general terms to ensure that the full range of raw intensity information is distributed across the full range of display intensities, and in specific terms to exaggerate the displayed intensity differences for the part of the raw data intensities that represent the tissue properties of interest.