Patent GB-1385232-A (GB)
Title: Producing colour record components for additive projection
IPC: G03B15/00
Filed: 1972-01-12
Abstract: 1385232 Producing colour record components for additive projection SPECTRAL DATA CORP 12 Jan 1972 [12 Jan 1971] 1541/72 Headings G2A G2C and G2J A plurality of photographs of a given scene that has arbitrary spectral characteristics and that is illuminated by an illuminant of arbitrary spectral characteristics are formed on black and white film using respectively different regions of the electromagnetic spectrum, the exposures respectively associated with the photographs being adjusted in accordance with the measured intensities of the radiation from the scene in each of the spectral regions so that each of the photographs is on a prescribed part of the characteristic curve of the film, reference images of the intensity of radiation from the scene in each of the spectral regions and of the intensity of the illuminant in each of the spectral regions are simultaneously recorded on the film, the film is developed and the photographs are projected in superimposed relation to form a composite image for viewing, the projection intensities of the respective photographs being adjusted as a function of the reference images e.g. so that the composite of the projected reference images is white. The exposures may be adjusted so that each of the photographs is on the same part, e.g. the straight line part, of the characteristic curve of the film. The invention also comprises a four-lens camera for use in the above process comprising means for measuring the intensity of the radiation from the scene in each of the spectral regions and for measuring the intensity of the illuminant in each of the spectral regions, automatic means for adjusting the exposures respectively associated with the photographs in accordance with the measured intensities of the radiation from the scene in each of the spectral regions and recording means for forming on the film a plurality of separate reference images that are functions respectively of the intensity of radiation from the scene in each of the spectral regions and of the intensity of the illuminant in each of the spectral regions. Fig. 1 shows a film strip (30) including four spectral photographs (32), (34), (36) and (38) and associated with each photograph a set of four fiducials (52), (54), (56) and (58) respectively and sets of grey-scale step wedges (32)-1 to (32)-4 being associated with photograph (32) and so on. The step wedges are used to form records on the film of the intensity of reflected radiation and the intensity of incident radiation in each spectral band. Fig. 2 is a view through the aperture plate (90) with the film and focal-plane shutter removed and shows camera lenses (72), (74), (76) and (78) mounted with their optical axes respectively intersecting the plane of the figure at (82), (84), (86) and (88) and projection lenses (72)-1 to 4, (74)- 1 to 4, (76)-1 to 4 and (78)-1 to 4 for step wedges (32)-1 to (38)-4. Fig. 3 (not shown) shows a curtain-type focal plane shutter (110) with the aperture plate (90) removed, but with the outlines of the apertures (92) to (98) and (102)-1 to (108)-4 shown in broken outline, and slits (112), (114), (116) and (118). Fig. 5 is a section through the line 5-5 of Fig. 2 and shows lens (76) and its associated filter (120) and iris diaphragm (122). Vacuum platen (124) and its suction line (125), two fiducial optical projection devices (150) and (152), optical projection devices (76)-1 to 4 which illuminate grey scale wedges (176)-1 to 4 respectively, automatic exposure control (AEC) servo (178) which controls lens diaphragm (122) and circular, variable density filter (194), incident radiation recording (IRR) servo (196) which reacts to radiation incident on the camera from the scene and controls circular, variable density filter (210) and step wedge projector (76)-4 which is unmodulated, has a filter (212) the same as the camera lens filter (120) and provides a sensitometric photographic record associated with each photograph employing radiation in the spectral region proper thereto. Figs. 10-12 (not shown) shows alternative embodiments of projection systems (76)-1 to 3. Fig. 23 shows means, for additively projecting photographs (388), (398), (392) and (402) on film (370) on to viewing screen (420) for observation from (422), comprising condenser lenses (372), (374), (376) and (378) and four additional condenser lenses (not shown), projection lamps (380), (382), (384) and (386) and four additional lamps (not shown) desaturation lamps (404) and (406) of adjustable intensity, half-silvered mirrors (408) and (410) and projection lenses (412), (414), (416) and (418). The step wedges are projected by fibre optics bundles (426), (428), (430) and (432) (only the middle two are shown in Fig. 23). The fibre optics bundles lead to the top of the viewer screen (420) and their exits are imaged by arrays of lenses (430) to form superimposed images.