C hapter 2 described light reflection in a theoretical, physical model, but the m easured d a ta in a recorded im age is influenced by the characteristics of the cam era. T his section covers the influence of such cam era charac­ teristics on the im age d a ta . Since some of these influences d istu rb the light reflection properties sta ted in the D ichrom atic Reflection Model, it is necessary to provide m ethods th a t restore the physical properties of light reflection. W here this is impossible, image analysis algorithm s m ust be able to detect or to lerate the inaccuracies in the im age d a ta . The images shown in th is book were taken in the C alibrated Im aging Laboratory [162] a t Carnegie Mellon University using a black-and-w hite C C D -cam era1 and spectral Alters3. This chapter describes the problem s occuring w ith such cam eras and dem onstrates the influence of shading, highlights, and cam era lim itations on pixel values in real images.