Mach Effect Correction

The Mach refers to an optical phenomenon where the inbuilt edge enhancement mechanism of the retina (where the edges of darker objects next to lighter objects will appear lighter and vice versa) create a false shadow ("Mach band") in a radiograph. Mach bands generally manifest adjacent to metal restorations or appliances and the boundary between enamel and dentin. This effect has been attributed as a source of diagnostic error in radiology.

By covering up the lighter object, such as a restoration, with a black square, one can reduce this effect and see the actual shade of gray present within the image pixel data without the brain trying to enhance the differentiation. For optimal results, the black square in the Mach effect correction tool should be angled parallel to the edge of the object and sized accordingly to cover it up.

To access this feature, simply look for this icon on the toolbar:

Then click and drag the black square along the image. You can right-click to rotate the square.

Mach Effect in action (Click to Enlarge)