GB907978A - Apparatus and method for the compression of color images - Google Patents

Abstract

907,978. Television. FAIRCHILD CAMERA & INSTRUMENT CORPORATION. Feb. 27, 1961 [March 1, 1960], No. 7107/61. Drawings to Specification. Class 40 (3). [Also in Group XL (c)] In an arrangement in which a coloured original (film transparency, photographic print &c.) is scanned photo-electrically to produce signals representative of the component colours thereof the range of both the luminance and the colour saturation of each point of the original is compressed (or expanded) without affecting the dominant wavelengths of the latter so that satisfactory reproduction by a different medium e.g. letterpress, gravure, lithographic printing &c. having ranges of luminance and saturation different from the original may be effected. The Specification gives a mathematical analysis of the problem and shows that the desired modification (" compression," in the described embodiments) may be effected by adding to each original colour component signal a colour saturation correction signal dependent on the instantaneous maximum and minimum values of the original signals and by multiplying each original colour component signal by a luminance correction signal also dependent on the instantaneous maximum and minimum values of the original signals. In one embodiment (Fig. 1, not shown), the correction signals are derived by computer means and caused to operate on the original signals at a point in the circuit subsequent to that at which they are derived. In a second, preferred, embodiment (Fig. 2, not shown), each colour component channel utilizes a photo-multiplier tube to the output of which the colour saturation correction signals, derived from a subsequent point in the circuit, are added the luminance correction signals, derived from the same point, being employed as modulation signals for the voltage supply to the dynodes of the multiplier. Specifications 692,349 and 692,400 and U.S.A. Specification 2,843,664 are referred to.