Embodiments of a system that includes one or more integrated circuits are described. During operation, the system transforms the video image from an initial brightness domain to a linear brightness domain, which includes a range of brightness values corresponding to substantially equidistant adjacent radiant-power values in a displayed video image. In this linear brightness domain, the system may determine an intensity setting of the light source based on at least a portion of the transformed video image, such as the portion of the transformed video image that includes spatially varying visual information in the video image. Moreover, the system may modify the transformed video image so that a product of the intensity setting and a transmittance associated with the modified video image approximately equals a product of a previous intensity setting and a transmittance associated with the video image. For example, the modification may include changing brightness values in the transformed video image.