BACKGROUND SEPARATION FOR STILL AND MOVING IMAGES

摘要

A method and apparatus is described in which by differential illumination, two separate picture signals can be obtained of a subject in front of a background one of which corresponds to a silhouette of the subject and a gating signal is derived from the silhouette size and the other a normal picture signal of the subject and the background. By using the gating signal, signal content of the subject from the background signal content in the said other picture signal, so the background can be sublimated relative to the subject for example by substituting for a "busy background" a plain neutral background which contains no shadow. Differential illumination is achieved using visible light followed by infrared light or vice versa or by illuminating the subject and background from the front for one scan and back illuminating the subject during the other scan, to produce the silhouette signal by illuminating the subject and the background by an intense source of illumination so that the subject appears very bright against a less bright background. By synchronously switching the video signal which contains image content relating to both subject and background, the latter can be removed from the subject image content so the latter can be superimposed onto a different background. A second secondary image may be produced using side or top illumination to cast a shadow adjacent a particular feature. Image analysis may be used to detect the position of the shadow to enable the feature position to be determined. The technique is of particular application to the automatic production of passport photographs.