Method for determining the exposure of a recording material

Claim 2

Method of photographically recording a multi-colored subject on a recording material which is spectrally sensitive to at least two different regions of the visible light spectrum corresponding to at least two colors of said subject, which method comprises the steps of: a. separately measuring the luminance of the colored subject in said at least two different spectral regions wherein the recording material is sensitive, b. exposing said at least two different spectrally sensitive regions of the recording material to a single radiation image transmitted by said color subject in said at least two different spectral regions, the extent of said exposure being adjusted substantially in accordance with said measured luminance of the subject in the region of the greatest luminance of said measured luminances, and c. developing the thus exposed recording material to produce the photographic recording of said subject.

Claim 3

Method according to claim 1, wherein the luminance of the subject is measured in the blue, the green and the red region of the spectrum.

Claim 4

Method according to claim 1, wherein the luminance of the subject is measured in the blue, the green and the red region of the spectrum.

Claim 5

Method according to claim 2, wherein the different luminances are measured simultaneously.

Claim 6

Method according to claim 2, wherein the different luminances are measured simultaneously.

Claim 7

Method according to claim 1 including the steps of separately filtering the light reflected from said subject to transmit light in each of the blue, green and red spectral regions, measuring the luminance of the light transmitted after such filtering in each of said regions, multiplying each such measured luminance by a factor equal to the ratio of the luminance of light reflected without filtration from an average grey subject to the luminance of the light from such average grey subject when correspondingly filtered, and adjusting the exposure of said material to said subject substantially in accordance with the largest of the thus multiplied luminance values. which is carried out in the method of the present invention is a reflected-light measurement. This notion should be broadly interpreted and includes the measurement of the light which is reflected by an opaque subject, as well as of the light which is transmitted by a transparent original, e.g., a colour-slide. This is distinct from the measurement of light which is falling on the subject, and which is known as incident-light measurement. An improved device for determining the exposure of a recording material which has to be exposed to a colour subject and which is spectrally sensitive in different regions of the visible spectrum may comprise at least two photo-electric cell means each of which is responsive to one of said different sensitivity regions of the recording material and produces an electric signal which is a measure of the luminance of the subject in said specific region. An exposure-meter according to the present invention may comprise : a. means for splitting a beam of incident light in the blue, the green and the red spectral region of the visible spectrum, b. three photoelectric cell means each of which receives light in one of said specific regions, c. three amplifiers for amplifying the electric signals produced by the said photoelectric cell means, and d. means for comparing the output signals of the amplifiers with each other and for selecting the signal which corresponds to the region in which the luminance is the greatest. The described arrangement, although appearing relatively complicated, may operate very reliable and may have very small dimensions, if use is made for the electronic part, of micro-electric elements such as integrated circuits. The photo-electric cell means may be of the photovoltaic type, e.g., a selenium cell or a silicium diode, of the photo-resistive type, e.g. a cadmium-sulfide light-depending resistor, they may comprise a phototransistor, a photomultiplier tube, etc. The exposure-meter may be an independent unit designed for operation with one hand, or it may be incorporated in the recording apparatus and the control of the exposure settings of such apparatus may occur automatically or through the intervention of the operator. The measurement by an inbuilt exposure-meter may occur through the lens of the recording apparatus or it may occur in the vicinity of the lens. The acceptance angle of the exposure-meter may be smaller than the taking angle of the recording apparatus and may even have a small value such as encountered in spotphotometers. The term ''''recording material'''' as used in the present specification, includes any material or system which is spectrally sensitive in at least two different regions of the visible spectrum, and wherein the colour subject is reproduced in the form of a negative or a positive image, or in the form of an electrical charge pattern. The metnioned recording material may be light-sensitive black-and-white or colour photographic film used in still picture photography, motion picture photography, telefilm recording, in a photographic copying or printing apparatus, etc., but it may also be the screen or screens of an image-recording tube or -system. The regions of the visible spectrum wherein the recording material is spectrally sensitive depend on the particular type of recording material. Thus, in the case of a conventional negative or reversal type of colour film, these regions are the blue, the green and the red part of the visible spectrum. In the case of a black and white film the regions are the blue and the green regions, for an orthochromatic, and the blue, the green and the red regions for a panchromatic film. It should be understood that the spectral sensitivity of the recording material may extend in a range or ranges outside the visible spectrum, and thus recoRding materials having a sensitivity which extends up into the UV or the IR region also lend themselves to an improved exposure a ccording to the method of the invention. The invention is described hereinafter with reference to the accompanying drawings wherein : FIG. 1 shows the spectral sensitization of a colour film. FIG. 2 is the spectral response of an exposure-meter. FIG. 3 is a diagram, wherein the reflectance of an average grey and a red subject are plotted. FIG. 4 is a diagram wherein the spectral skin reflectance is plotted. FIG. 5 shows diagrammatically the optical arrangement in a motion picutre camera for measuring the luminance of the subject in three different regions. FIG. 6 is the electronic circuit for selecting the signal of greatest luminance. In FIG. 1 the spectral sensitivity curves of a common photographic colour reversal material are shown, which have been determined by means of a common spectrosensitometer using an incandescent tungsten filament operating at a temperature of 3, 200*K. The curves are plotted as effective response to the lamp. The parameter lambda of the graph represents the wavelength in nm, whereas E is the energy distribution of the light source of 3,200*K and S is the sensitivity of the material as a function of the wavelength. In FIG. 2 the spectral response of the exposure-meter which is used in the present expample, is shown. The curve generally corresponds to the spectral sensitivity of the eye and is also plotted as effective response to a lamp operating at 3,200*K, s being the sensitivity of the meter as a function of the wavelength, and E being again the energy distribution of a light source of 3,200*K. The exposure-meter is calibrated according to the speed of the colour material to indicate the exact exposure, i.e., exposure time and diaphragm opening. If an average grey scene is recorded, see the line drawn in full in the diagram of FIG. 3, the exposure-meter will give the following indication Ee of the integrated effective light quantum reaching the photo-sensitive cell of the meter.

Claim 8

Method according to claim 1 including the steps of separately filtering the light reflected from said subject to transmit light in each of the blue, green and red spectral regions, measuring the luminance of the light transmitted after such filtering in each of said regions, multiplying each such measured luminance by a factor equal to the ratio of the luminance of light reflected without filtration from an average grey subject to the luminance of the light from such average grey subject when correspondingly filtered, and adjusting the exposure of said material to said subject substantially in accordance with the largest of the thus multiplied luminance vlues.