Patent US 3,936,598

A television camera provides a video output voltage having an amplitude proportional to an amount of light flux received along a line of sight which traces a raster on a scene. In response to the video output voltage, an antilog amplifier provides an image photo-density voltage having an amplitude proportional to the image density of a point on the scene along the line of sight. The amplitude of the density voltage is compared in a window detector to a pair of window voltages which define a voltage range. The window detector provides first and second voltages in response to the density voltage being respectively within and outside of the voltage range. Selected frequency components of the output of the window detector are provided to a display for displaying a representation of objects of the scene, where the displayed objects have a size within a selected range of sizes and have an image within a selected range of image densities.