JPH02216422A - Exposure meter - Google Patents

Abstract

PURPOSE:To always obtain a correct exposure irrespective of an average reflection factor of an object to be photographed by estimating a reflection factor of the object to be photographed from chromaticity, and correcting a difference to a reference reflection factor against an exposure value. CONSTITUTION:A light beam from an object to be photographed is given to photoelectric converting circuits 13, 23 and 33 through filters 11, 21 and 31, and colorimetry use photodetectors 12, 22 and 32, respectively. Sample holding signals Sx-Sz outputted from sample holding circuits 14, 24 and 34 through the converting circuits 13-33 are switched successively and inputted to an arithmetic part 3 through an A/D converting circuit 1. The arithmetic part 3 calculates an exposure value by an A/D conversion value of the signal Sy, and calculates chromaticity values as (x)-(z), based on the A/D conversion values of the signals Sx-Sz. From memory information of a memory part 2 corresponding to the chromaticity values (x)-(z) calculated therein, exposure correction data is referred to or calculated, and a corrected exposure value is calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an exposure meter, and more particularly, to an exposure meter that accurately measures the intensity of a subject and calculates an appropriate exposure value when taking a photograph.

[Prior Art] In general, the exposure value in a conventional external light exposure meter, which is calculated by measuring the reflected light from the subject with a photometric sensor, is as follows:
It is formed by assuming that the light reflectance of the subject is approximately constant.

Specifically, the highest reflectance seen in general subjects9
It is designed to calculate the exposure value assuming an average reflectance of around 18%, which is the geometric mean of 0% and the lowest reflectance of 3%.

By the way, this average reflectance means that the average reflectance of landscapes, people, and other subjects photographed with a camera is approximately 18%, and the average reflectance of each individual subject is of course limited.

[Problems to be Solved by the Invention] However, when a subject whose reflectance is lower than 18% is photometered using an external light exposure meter, the photometric value will show a lower luminance than the actual luminance. Therefore, the exposure value obtained by photometering such a subject ends up being overexposed compared to the appropriate exposure. Also, if it is the other way around, the image will be underexposed. In this way, the conventional light meter calculates an appropriate exposure value only for a subject whose average reflectance is 18%.

In other words, since external light exposure meters have these drawbacks, when using a narrow latitude film such as reversal film, an incident light exposure meter is used to avoid the effects of the reflectance of the subject. In many cases, a photometry method that is not used is adopted. However, since photometry using this incident light type exposure meter requires going to the position of the subject to measure the light, it is very inconvenient for the photographer.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned problems and to capture the brightness of a subject from the photographer's position with a camera.
To provide an exposure meter that can always obtain proper exposure regardless of the average reflectance of a subject.

[Means for Solving the Problems and Work 1] 1] The exposure meter of the present invention includes a photometry means for measuring the brightness of a subject, a color embellishing means for measuring the chromaticity of the subject, and a light meter for measuring the subject's brightness based on the measured chromaticity. The present invention is characterized by comprising a correction calculation means for estimating the reflectance and correcting the difference from the base reflectance to an exposure value based on the output of the optical means.

[Embodiment j] Hereinafter, the present invention will be specifically described with reference to the drawings. First, prior to a detailed explanation of the present invention, the spectral sensitivity distribution of light will be explained using FIG.

Figure 2 is a characteristic diagram showing the spectral sensitivity distribution of spectral stimulus values ma (λ), y (λ), and 7 (λ) in the CIE 2-degree visual field XYZ color system, where the vertical axis represents the stimulus value and the horizontal axis represents the spectral sensitivity distribution. FIG. 3 is a diagram plotted against the wavelength λ shown in FIG. In the figure, the curve Ω1 exhibiting an irregular double peak shape and having a peak in the longest wavelength region represents the spectral stimulation value ma(λ), and the single peak curve II2 having a peak in the intermediate wavelength region represents the spectral stimulation value y( A curve fI3 having a peak in the shortest wavelength region of λ) represents the spectral sensitivity distribution of each spectral stimulus value i(λ). As is clear from the figure, these three curves N1. The curve i12 among R2 and N3 is
It can be seen that the distribution approximately matches the standard spectral sensitivity distribution of the human eye.

Next, the first embodiment of the present invention will be explained using FIGS. 1 and 3.
This will be explained in detail below. FIG. 1 is a structural block diagram of a light meter showing a first embodiment of the present invention. In the figure,
Reference numerals 11, 21, and 31 are wavelength selective filters (hereinafter abbreviated as filter output), and 12, 22, and 32 are color embellishing light-receiving elements (hereinafter abbreviated as light-receiving elements). The combination of the filter 11 and the light receiving element 12 produces the spectral stimulation value y(λ) explained in FIG.
), each spectral sensitivity distribution of the spectral stimulation Ef1z (λ) can be obtained by the combination of the filter 31 and the light receiving element T32.

The light receiving elements 12, 22.32 photoelectrically convert the photocurrent signals outputted from each light receiving element to generate a voltage signal V1. V2.
They are respectively connected to sample and hold circuits 14°24.34 via photoelectric conversion circuits 13°23.33 for converting to V3. This sample hold circuit 14, 24.3
4 is the above spectral stimulation value ma(λ), y(λ), i(
A/D conversion circuit 1 that samples and holds λ), respectively, and converts analog values into digital values via selection switches 15 and 25.35 that select the obtained sample hold signals SX, Sy, and Sz, respectively. It is connected to the.

A built-in CP connected to the A/D conversion circuit 1 and a memory section 2 in which correlation information between chromaticity and reflectance is stored.
The calculation unit 3 that performs calculations in U is connected to an exposure control unit 4 that controls exposure in automatic exposure, and an exposure value display unit 5 that digitally displays exposure values.

When the light meter shown in the first embodiment configured as described above is applied to an eye reflex camera,
FIG. 3 shows an example of how photometry and colorimetry elements are attached to a camera. In the figure, reference numeral 51 is a photographing lens, 52 is a movable reflection mirror, and the center portion 53 is a half mirror.

Reference numeral 54 denotes a sub-mirror which serves to cause light from the object to enter a group of colorimetric elements 55 disposed at the bottom of the camera. Reference numeral 57 denotes a focusing plate, and numeral 56 a pentaprism, both of which together with the movable reflecting mirror 52 constitute a finder optical system. In this camera, a part of the subject light that has passed through the photographic lens 51 passes through a half mirror 53 provided at the center of the movable reflective mirror 52.
A sub-mirror 54 provided on the back surface of the reflective mirror 52
The light is reflected by the camera, and an image is formed on the light-receiving surface of a photometric and colorimetric element group 55 arranged at the bottom of the camera. This 1N light and colorimetric element group 55 includes the filters 11 and 21 shown in FIG.
．． 31 and light receiving elements 12, 22, and 32 are appropriately arranged.

On the other hand, the subject light reflected by the movable reflection mirror 52 and directed toward the finder optical system arranged above in the figure is
The light enters the pentagonal prism 56 via the focus plate 57 and reaches the finder eyepiece (not shown).

Next, the operation of the first embodiment of the present invention configured as described above will be explained. A part of the subject light transmitted through the photographing lens 51 shown in FIG.
4 to the filter 11゜21.31 and the light receiving element 1
2.22.32 (See Fig. 1 above) When the ApJ color tooth element group 55 is irradiated, the subject light passes through a filter 11°21.31 to obtain a spectral stimulation value map (λ
), y(λ) and i(λ) components, which are output from the light receiving element 12°22.32 and sent to the photoelectric conversion circuit 13.23.
The voltage signal photoelectrically converted at .degree. 33 becomes a signal corresponding to the spectral stimulation value ma(.lambda.), V(.lambda.), and i(.lambda.) components.

By the way, originally, the light receiving element for photometry and the light receiving element for colorimetry are provided separately. However, in this first embodiment, color embellishment is performed based on the CIE 2-degree visual field XYZ color system, as explained with reference to FIG. Therefore, the spectral stimulation value y(λ
) is almost the same as the standard spectral sensitivity distribution of the human eye, it can be obtained by combining the filter 21 and light receiving element 22 that correspond to the 7 (λ) components of the above color system. The photoelectric conversion output for color embellishment is used as it is for 71P1 light. In addition, the colorimetric photoelectric conversion output obtained by each combination of the filter 11 and the light receiving element 12, and the filter 31 and the light receiving element 32 is x of the color system mentioned above.
, corresponds to the z component as described above.

The sample-and-hold signals Sx, Sy, and Sz output from the sample-and-hold circuits 14, 24, and 34 via the photoelectric conversion circuits 13, 23, and 33 are sent to the selection switches 15, 25, .
35, A/D conversion is performed by the A/D conversion circuit 1, and the signal is taken into the arithmetic unit 3.

The arithmetic unit 3 uses a CPU stored therein to calculate an exposure value as a photometric value using an A/D converted value of a sample hold signal Sy corresponding to the y component of the color system. In addition, in addition to color embellishment values, A/
The chromaticity value is calculated as X*Y,z based on the D conversion value. Exposure correction data is referred to or calculated from memory information in the memory unit 2 corresponding to the chromaticity value xr'j+Z calculated here, and a corrected exposure value is calculated.

Automatic exposure is performed by the exposure control section 4 based on the corrected exposure amount calculated by the calculation section 3, and the exposure value is displayed on the exposure display section 5.

Next, the exposure calculation by the CPU stored in the calculation section 3 will be explained in more detail based on the flowchart shown in FIG. First, each constant used in the flow chart of FIG. 4 will be summarized and explained below before explaining each step.

The data taken into the arithmetic unit 3 from the A/D conversion circuit 1 shown in FIG. 1 is a voltage signal V1. V2°v3, and the voltage values are also expressed as vl, v2.v3 using the same sign, respectively. Set it as v3.

The exposure value Ev is the exposure value before correction assuming that the subject reflectance is 18%, and E'V is the exposure value after correction. Further, town is a constant determined to obtain a correct value when the exposure value is calculated using the formula shown in equation (1) below, and K1°K2.
In order to correctly calculate the chromaticity XIY, 3 is a constant determined so that Kt Vl""K2 V2"Ka Va at equal energy white + 31 constant time.And these constants KE,
K1. 2, Ka is stored in the memory section 2.

When the calculation starts, first, in step S1, the constant KE is set to 2. 3 is read from the memory section 2. Then, the process proceeds to step S2, where the voltage signal Vt
, V2, and Va are read from the A/D conversion circuit 1. Next, in step S3, the exposure value Ev is calculated using the following formula.

E v-13og2KE V2 - (1) In step S4, the chromaticity value X+3/ is calculated using the following formula.

KlV.

In step S5, the exposure correction value Δ is based on the estimated reflectance corresponding to the chromaticity values x and y obtained in step S4.
E is read from the memory section 2. Then, the process proceeds to step S6, and the corrected exposure value E'v is calculated using the following equation.

E'v=Ev+ΔEv The corrected exposure value E'v thus obtained is displayed on the exposure value display section 5 in step S7, and the process proceeds to step S8, where the exposure control section 4 is operated based on the corrected exposure value E'v.

Next, the background behind such exposure correction will be explained using FIGS. 5 to 7.

FIG. 5 is a chromaticity diagram based on an orthogonal coordinate system of chromaticity coordinates x and y. Chromaticity is usually expressed by its component values X+ yl z, but each component X+ ! Since there is the relationship x+y+z-L, 0 between /+z, all colors existing in nature can be represented if two arbitrary variables, for example, X and y, are determined. Therefore, in a chromaticity diagram, chromaticity is usually expressed using an orthogonal coordinate system of chromaticity coordinates x and y, with X on the horizontal axis and y on the vertical axis.

The chromaticity diagram shown in FIG. 5 shows the distribution of correction values based on the chromaticity and subject reflectance stored in the memory section 2. In the figure, the solid line f! The area surrounded by 4 is the area where the actual color exists, and the closer you go to the periphery of that area, the more vivid the color becomes. It shows that the saturation used becomes higher, and conversely (x, V, z) −<0.33. O40
, 0, 33) is achromatic.

In this first embodiment, the low saturation part near the center of FIG. In the area of high saturation part 42, positive correction is performed to increase the exposure amount by +1.5Ev, and in the area of high saturation part 43 near green-blue-purple, minor correction is performed to decrease the exposure amount by 5Ev. . The basis for such exposure correction will be explained next using FIG. 6.

FIG. 6 is a diagram showing the results of measuring a large number of colored papers with object reflectance of 18% but different chromaticities under sunlight on the same chromaticity diagram as in FIG. 5 above.

As is clear from the figure, depending on the chromaticity of the colored paper, the solid line Ω4
A distribution like -10 was obtained.

Here, + is the chromaticity point of something that shows a value of +0.5 Ev or more with respect to an object with 18% reflectance, and - indicates a value of -0.5 Ev or less with respect to an object with 18% reflectance. It is the chromaticity point of an object, and 0 is -0, 4 for an object with a reflectance of 18%.
~+〇, 4Ev chromaticity point. In other words, there is a tendency to correct as described above depending on the chromaticity of colored paper, and this tendency also generally applies to cloth and painted metal.

Furthermore, as is clear from the diagram showing the correlation between brightness and saturation created from the appendix of Japanese Industrial Standard 28721 "Color display method according to three attributes" shown in Figure 7, the curve g5 corresponding to yellow-green color has a high reflectance, and the curve Ω corresponds to a blue-violet color.
6 has a low reflectance, and the curve g7 corresponding to red color is neutral, but the distribution is such that it can be said with higher certainty that the curve g7 corresponding to the red color is neutral.

That is, the exposure meter according to the first embodiment described above includes a light receiving element 22 as a photoelectric conversion section for photometry having a spectral sensitivity approximately equal to the standard spectral sensitivity of the human eye, and a filter 11, 21 that filters light from a subject. Information regarding the correlation between chromaticity and reflectance and the light receiving elements 12 and 22.32 as photoelectric conversion units for 11-1 colors that photoelectrically convert the light of the basic color components according to .31. Memory section 2 for storing data and the above? i-" a calculation section 3 that estimates the reflectance of the subject from the output of the receiving photoelectric conversion section and the information in the memory section, and corrects the exposure amount obtained from the photometry photoelectric conversion section based on the estimated reflectance; It is equipped with

Therefore, according to the first embodiment, it is possible to calculate the exposure amount and perform automatic exposure in the same manner as before for subjects with low saturation, and to shoot subjects with high saturation, such as bright yellow flowers and painted surfaces. If you want to take pictures of bright blue-purple clothes, painted surfaces, etc., negative compensation is applied, so you will not be overexposed like in the past. In either case, proper exposure can be obtained.

FIG. 8 is an optical path diagram of essential parts of an exposure meter showing a second embodiment of the present invention. In the first embodiment, the spectral sensitivity distribution corresponding to the y(λ) component of the CIE 2-degree visual field XYz color system is indistinguishable from the standard spectral sensitivity distribution of the human eye. λ) component is also used for photometry, thereby omitting the light receiving element for n1 light, but in this second embodiment, the light receiving element for AIJ color is separated and a separate light receiving element for photometry is provided.

In the figure, a prism 71 and a light-receiving element array 72 constitute a color measurement section. Moreover, the code 73 is the half mirror 1
74 is a light receiving element for photometry.

The object light is divided by the half mirror 73 into the direction of the prism 71 and the direction of the m1 light receiving cable 74.

The light passing through the prism 71 is separated into monochromatic lights and enters the light receiving element array 72. Above, 1111 light receiving element 7
The light incident on the light receiving element array 72 for colors 4 and ΔF1 is photoelectrically converted and A/D converted in the same manner as in the first embodiment, and then the memory information in the memory section 2 (see FIG. 1) is The appropriate exposure is calculated and the exposure is displayed.

According to the second embodiment with such a configuration, since a photoelectric conversion output of monochromatic light can be obtained, by calculating in the calculation section,
It is possible to discriminate colors based not only on the CIE 2-degree visual field XYz color system but also on any color system, and perform exposure correction using the correlation between chromaticity and reflectance.

FIG. 9 is an optical path diagram of essential parts of a light meter showing a T13 embodiment of the present invention. The third embodiment differs greatly from the second embodiment in that a diffraction grating is used instead of a prism to separate the subject light into monochromatic light. A color measurement section is configured.

That is, in this third embodiment, the subject light is decomposed into single wavelengths by the diffraction grating 81 and enters the light receiving element array 82. By calculating the photoelectric conversion output of this light-receiving element array 82, in addition to the above-mentioned Δ-1 light output, it is possible to add color based on any color system, and to calculate the above-mentioned photometric and 11-color output as well as chromaticity and reflectance. A corrected exposure value can be calculated based on the memory information regarding the correlation.

In addition to the above-mentioned embodiments, it is also possible to use a CCD area sensor with a color filter used in video cameras as a light receiving element to measure chromaticity based on a video signal and use it for exposure compensation. . Further, the photoelectric conversion output may be processed by logarithmically compressed, and it goes without saying that a dedicated A/D conversion circuit may be provided for each light receiving element.

Furthermore, if the subject is limited in advance, or the light source and other conditions are determined in advance, it is possible to make very fine exposure adjustments by preparing special memory information for correction according to the conditions. It goes without saying that correction is also possible. [Effects of the Invention] As described above, according to the present invention, the reflectance of the subject is not uniformly set to 18% as in the past, but the light from the subject is The system separates the basic color components into basic color components, measures the chromaticity, and corrects the exposure value based on the relationship between the chromaticity stored in memory and the reflectance of the subject, making it possible to always output the correct exposure value. The effect is demonstrated.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a light meter according to a first embodiment of the present invention. FIG. 2 is a block diagram of a light meter according to a first embodiment of the present invention. Figure 3 shows the characteristic diagram showing the spectral sensitivity distribution of #TP1 light and the light-receiving element for lubricating when the light meter shown in Figure 1 above is applied to a single-lens reflex camera. Figure 4 is a flow chart showing the exposure calculation in the calculation unit in Figure 1 above; Figures 5 and 6 are chromaticity diagrams based on the orthogonal coordinate system of chromaticity coordinates x and y; Figure 5 shows the correction values based on the chromaticity and subject reflectance shown together on this chromaticity diagram, and Figure 6 shows the correction values of many colored papers with different chromaticities under sunlight. FIG. 7 is a characteristic diagram showing the correlation between brightness and saturation. FIG. 8 is an optical path diagram of the main parts of the exposure meter showing the second embodiment of the present invention. The figure is an optical path diagram of main parts of an exposure meter showing a third embodiment of the present invention.

Claims (2)

[Claims] (1) A photometric means for measuring the brightness of the subject; a colorimetric means for measuring the chromaticity of the subject; and a colorimetric means for estimating the reflectance of the subject from the measured chromaticity and calculating the difference from the reference reflectance. A light meter comprising: a correction calculating means for correcting an exposure value based on an output. (2) The exposure meter according to claim 1, wherein the colorimetric means also serves as the photometric means, and the subject brightness is determined from a part of the output of the colorimetric means.