Graphical interpretation of text Equation (3) for computing the polychromatic PSF as the sum of luminance-weighted monochromatic PSFs. For each wavelength in the source spectrum, a monochromatic PSF is computed from monochromatic aberrations plus the focal shift associated with LCA and the lateral displacement associated with TCA; the diagram shows three such PSFs schematically as blur disks of varying diameter. The luminance weighting of each blur disk is given by the height of the source spectrum curve shown below the LCA curve. (Courtesy Ravikumar et al. [(2008 Oct) J. Opt. Soc. Am. A Opt. Image Sci. Vis., 25, 10, 2395–2407]).