JPH02253124A - Exposure meter - Google Patents

Abstract

PURPOSE:To always obtain an accurate exposure value by measuring the chromaticity of an object, estimating the reflectance of the object by fuzzy inference and correcting and operating the exposure value based on the estimated reflectance. CONSTITUTION:Light from the object and light from an illuminating light source are respectively made incident on filters F1-F6, photoelectrically converted E1-E6 and sample-held H1-H6 to successively turn on selection switches S1-S3 and S4-S6. Then, they are successively A/D converted 1 and inputted in an arithmetic control part 3. The arithmetic control part 3 calculates the chromaticity, brightness and the exposure value corresponding to reference reflectance based on the brightness of the object and calculates the chromaticity of the illuminating light source. Then, it performs the fuzzy inference 4 based on the chromaticity value of the object and the illuminating light source and membership function stored in a memory 2 and outputs a correction value for the reference reflectance corresponding to the reflectance estimated from the chromaticity value. The accurate exposure value is calculated by correcting and operating the exposure value and displayed on a display part 5 so as to perform automatic exposure by an exposure control part 6.

Description

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

[Prior art] In general, the reflected light from the subject is measured using a photometric sensor, etc.
The exposure value in a conventional external light type exposure meter, which is calculated using 11 lights, is calculated 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%, so 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 photometer 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, when it's the other way around, it becomes an exposure amplifier. In this way, conventional external light exposure meters have an average reflectance of 18%.
The correct exposure value is calculated only for the subject.

In other words, external light exposure meters have these drawbacks, so when using a film with a narrow latitude, such as a reversal film, an incident light exposure meter is used to measure the subject. A photometry method that is not affected by reflectance is often used. However, light metering using this incident light type exposure meter is very inconvenient for photographers because it is necessary to go to the subject's position and measure the light.

The present invention was made with attention to such problems,
To provide a light meter which can always obtain proper exposure regardless of the average reflectance of the subject, without measuring the brightness of the subject from the position of a photographer with a camera.

[Means for solving the problem] The exposure meter of the present invention has a Δ
The reflectance of the subject is estimated by fuzzy inference from the chromaticity of the subject measured by the colorimetric means, and the difference from the reference reflectance is calculated by calculating the difference from the reference reflectance. A correction means is provided for correcting the exposure amount based on the sensitivity of the light means.

[Function] The light meter of the present invention measures the chromaticity of the subject, estimates the reflectance of the subject from the reflectance tendency of objects with this chromaticity, and corrects the exposure value based on this estimated reflectance. By performing the calculation, an accurate exposure value can be determined.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

1 to 5 show a first embodiment of the exposure meter of the present invention. Figure 1 shows the block configuration of the exposure meter, where F1 to F6 are wavelength selective filters, respectively.
6 are light receiving elements for colorimetry. Here, the combination of filter F and light receiving element P1, and the combination of filter F4 and light receiving element P.

Similarly, the combination of filter F2 and light receiving element P2 and the combination of filter F5 and light receiving element P5 have a spectral sensitivity of the spectral stimulation value (see X(λ) in FIG. 3).
The combination of the filter F3 and the light receiving element P3 and the combination of the filter F6 and the light receiving element P6 have the spectral sensitivity of the spectral stimulation value (see y(λ) in Figure 3). (see 2(λ) in FIG. 3).

E1 to E6 are photoelectric conversion circuits connected to the light receiving elements P1 to P6, respectively, and H1 to H6 are sample and hold circuits that sample and hold the portions of the photoelectric conversion circuits E1 to E6, respectively. 81 to S6 are selection switches for selecting the output values of the sample and hold circuits H1 to H6; 1 is an analog/digital (A/D) conversion circuit commonly connected to each of the selection 8 outputs of the selection switches 81 to S6; 2
3 is a memory in which membership functions and the like used for fuzzy inference (described later) are stored; 3 is an arithmetic control unit that calculates chromaticity values and exposure values; and 4 is a fuzzy inference unit that performs fuzzy inference; Reference numeral 5 represents a display section for displaying exposure values, etc., and reference numeral 6 represents an exposure control section for performing automatic exposure.

A block 8 including filters F1 to F3, light receiving elements P1 to P3, photoelectric conversion circuits E1 to E3, sample and hold circuits H1 to H3, and selection switches 81 to s3 is part of a colorimeter for measuring the chromaticity of an object. It also serves as a photometer for measuring the brightness of the subject. Similarly, filters F4 to F6, light receiving elements P4 to P6, photoelectric conversion circuit E1. ~E6, sample hold circuit H1~H6,
and selection switch S1. The block 9 with ~S6 is part of the embellishment means for measuring the chromaticity of the illumination source.

FIG. 2 shows an example of the arrangement of the exposure meter in a single-lens reflex camera to which the exposure meter shown in FIG. is a half mirror 23. A sub-mirror 24 has the role of transmitting light from a subject to a photometric/colorimetric element 25 disposed at the bottom of the camera. 26 is a color embellishment element for measuring the chromaticity of the illumination light source, 27 is a pentaprism, and 28 is a focus plate.

Note that the photometric/coloring element 25 is the filter F in FIG.
1 to F3 and correspond to the light receiving elements P1 to P3, and the colorimetric element 2
6 are filters F4 to F6 and light receiving cables P4 to P in FIG.
Corresponds to 6.

Next, before explaining the present invention in detail, the spectral sensitivity of light will be explained with reference to FIG. 3, and the outline of fuzzy inference will be explained with reference to FIG.

Figure 3 is a characteristic diagram showing the spectral sensitivity distribution of spectral stimulus values X(λ), y(λ), and 2(λ) in the CIE 2-degree visual field XYZ display system, with respect to the wavelength λ shown on the horizontal axis. The stimulation value is plotted on the vertical axis. In this figure, the irregular double-peaked curve with a peak in the longest wavelength region is the spectral sensitivity distribution of the spectral stimulus value X(λ), and the curve with a peak in the intermediate wavelength region is the spectral stimulus value y(λ). ), and the curve having a peak in the shortest wavelength region represents the spectral sensitivity distribution at a spectral stimulus value of 2 (λ). As is clear from this figure, these three curves almost match the standard spectral sensitivity distribution of the human eye.

On the other hand, fuzzy inference is inference using fuzzy rules (fuzzy inference rules) expressed in ambiguous words that humans use in their daily lives. fuzzy rules rif
A-BIG andB=NORMAL the
n It can be written like X-3MALLJ.

In FIG. 10, A and B are input variables, and X is an output variable. The part that describes the conditions for the rule to hold, l''A=BIG and B-NORMALJ, is called the antecedent part, and its conclusion part, rX-3MALLj, is called the consequent part.In fuzzy inference, each input variable is set to 0. The calculation is performed by converting it into a value of ~1, and the membership function (antecedent membership function) defines this conversion.

The membership function is a proposition (
BIG, NORMAL, SMALL, etc.). The degree to which the input variables satisfy each proposition is calculated by referring to the membership function. If there are multiple propositions in the antecedent part, find the minimum value among them. Set this to the minimum value (
This is called the M I N) operation. Next, the membership values for each rule are combined. This is done by comparing the consequents of each rule, taking the maximum value, and creating a new membership function. This is called maximum value (MAX) calculation. The centroid value of this combined membership function becomes the inference result (output value), and subsequent control is performed based on this.

Although a typical example of the fuzzy inference method is shown in FIG. 10, various other fuzzy inference methods have been proposed.

Next, the operation of the exposure meter of this embodiment will be explained in detail. Light from the subject passes through the photographic lens 21, and a portion of it passes through the half mirror 23 and sub mirror 24 in order to become a side light.
The color measurement element 25 is reached.

That is, the light passes through filters F1 to F3, enters light receiving elements P1 to P3, and is photoelectrically converted by photoelectric conversion circuits E1 to E3.

Here, the light receiving element for photometry and the light receiving element for embellishing originally exist separately, but in this embodiment, since colorimetry is performed based on the CIE 2-degree visual field XYZ display system, the filter F2 and the light receiving element P2 are The photoelectric conversion output obtained by the combination corresponds to the y component of the display system, and this is the same as the standard spectral sensitivity distribution of the human eye, so
It can also be used for photometry. The photoelectric conversion output obtained by the combination of the filter F1 and the light receiving element P1 and the combination of the filter F3 and the light receiving element P3 correspond to the x and z components of the display system. The value of the output photoelectrically converted by the photoelectric conversion circuits E1 to E3 is sent to the sample hold circuit H1.
~ Sample and hold by H3, selection switch 81
~S3 are turned on sequentially, so that the sample and hold outputs are sequentially A/D converted by the A/D conversion circuit 1, and then
Input to the calculation control section 3.

On the other hand, the light from the illumination light source enters the colorimetric element 26. That is, the light passes through filters F4 to F6, enters light receiving elements P4 to P6, and is photoelectrically converted by photoelectric conversion circuits E4 to E6. A combination of filter F4 and light receiving element P4, and a combination of filter F5 and light receiving element P5,
The photoelectric conversion output obtained by the combination of filter F6 and light receiving element P6 corresponds to the xSy and z components of the display system. The values of the outputs photoelectrically converted by the photoelectric conversion circuits E4 to E6 are sampled and held by the sample and hold circuits H1 to H6, and by sequentially turning on the selection switches 571 to 86, the values of the outputs are sampled and held by the A/D conversion circuit 1. After the /D conversion, the signal is input to the arithmetic control section 3.

Based on the input A/D conversion data as described above, the calculation control unit 3 calculates the chromaticity of the subject, the brightness, and the exposure value corresponding to the reference reflectance based on the brightness, and also calculates the chromaticity of the illumination light source. Calculate. Next, fuzzy inference is performed in the fuzzy inference means 4 based on the chromaticity values of the subject and the illumination light source and the membership functions stored in the memory 2, and the reflectance estimated from the chromaticity values is A correction value for the corresponding reference reflectance is output.

Based on this correction value and an exposure value corresponding to a reference reflectance calculated in advance, a correction calculation is performed in the calculation control section 3, and a correct exposure value is calculated. Based on the correct exposure value calculated by this correction calculation, the exposure value is displayed on the display section 5, and the exposure control section 6 performs automatic exposure.

As described above, the light meter of this embodiment measures the chromaticity of the subject, estimates the subject's reflectance from the reflectance tendency of objects with this chromaticity, and then sets the exposure value based on this estimated reflectance. An accurate exposure value can be determined by performing a correction calculation.

Next, fuzzy inference in this embodiment will be specifically explained. FIG. 4 shows the membership functions stored in the memory 2. The antecedent part is the four-person power, and is the chromaticity value x, y of the illumination light source and the chromaticity value x, y of the subject. Rule R]~R7 is sunny day, shadow light, rule R8~R14
indicates sunlight, and rules R15 to R21 correspond to light bulb light, and the chromaticity values x and y under that light and the exposure correction value based on the estimated reflectance at that time are shown.

For example, in rule R8, ``If the chromaticity value is x=0.592, y=o, 3 under a light source with chromaticity such as sunlight,
16 (C8 in FIG. 5), the correction value based on the estimated reflectance is ±OEV."

Here, the chromaticity diagram corresponding to rules R8 to R1, 4 is
As shown in the figure. This chromaticity diagram shows the distribution of correction values based on chromaticity and subject reflectance in an orthogonal coordinate system of chromaticity coordinates X and y, and the antecedent chromaticity values x, y of rules R8 to R14
The points where the membership value corresponding to "]" is 08 to C
It is represented by 1 and 4. In addition, under sunlight, the distribution of exposure correction values obtained from actual measured values of reflectance mainly of paper is shown. ,4EV 〜→-0,4EV to ``0
”. The membership functions of this embodiment are created based on the measurement results shown in FIG.

According to the first embodiment described above, even under any illumination light source or at any chromaticity point, the exposure correction value based on the estimated reflectance can be easily calculated by fuzzy reasoning.
[3] It is possible to output the correct exposure value. Therefore, the amount of memory required is much smaller than when the estimated reflectance and the exposure correction value based on it are stored in memory in advance for every chromaticity point under every illumination light source.

Note that in the first embodiment, the accuracy can be further improved by increasing the number of fuzzy inference rules and setting more detailed rules regarding the illumination light source and chromaticity values.

Furthermore, the fuzzy inference method is based on the MIN used in the above example.
It is also possible to use a calculation other than the MAX calculation.

Furthermore, the method of displaying the measured values may be RGB system, Lab system, or other methods, and the value of a color temperature sensor may be used as the illumination light source.

Next, a second embodiment of the present invention will be described with reference to FIGS. 6 and 7. In the first embodiment, a light meter built into a camera was shown, but in this second embodiment, a light meter alone is shown.

That is, compared to the exposure meter shown in FIG. 1, the exposure meter shown in FIG. 6 has filters F4 to F6 and light receiving elements P4 to P6.
, photoelectric conversion circuits E4 to E6, sample and hold circuit H4
~H6 and the selection switches 84 to S6 are omitted, and the function of the arithmetic control section 3' is different. Furthermore, it is possible to manually specify the illumination light source to the fuzzy inference means 4 from the illumination light source specifying device 71. 1, and the other points are almost the same, so the same reference numerals as in FIG. 1 are used. The arithmetic control unit 3' calculates the chromaticity of the subject, the brightness, and the exposure value corresponding to the reference reflectance based on the brightness based on the input A/D conversion data, but it does not calculate the chromaticity value of the illumination light source. will not be carried out.

FIG. 7 shows an example of the cross-sectional structure of the light meter shown in FIG. 6, where 80 is the light meter housing, 81 is the objective lens, and 82
A half mirror 83 is a photometric/coloring element disposed at the bottom of the housing 80, 84 is an eyepiece, 85 is a photometric vessel, and 86 to 88 are clear day, shadow light designation buttons of the illumination light source designation device 71, respectively. , sunlight specification button, and bulb light specification button. Note that the photometric/coloring element 83 is the filter F1 in FIG.
~F3 and the light receiving elements p and -p3.

Next, the operation of the exposure meter of this second embodiment will be explained in detail. The light from the subject is passed through the objective lens 81 and half mirror 82.
The light then reaches the photometric/colorimetric element 83. On the other hand, the light from the subject is separated by a half mirror 82, and a portion of it reaches an eyepiece 84. The measurer can determine the measurement direction by looking through the eyepiece 84. At the time of measurement, the measurer specifies the illumination light source by pressing the button 86 for clear weather/shade light designation, the sunlight designation charter boat 87, or the bulb light designation button 88 of the illumination light source designation device 71, and then selects the photometry charter boat 85. Press this button to perform photometry.

The light that reaches the photometry/colorimetry element 83 is subjected to photoelectric conversion and A/D conversion as in the first embodiment, and the arithmetic and control unit 3' calculates the chromaticity and brightness of the subject, and the reference reflection based on the brightness. An exposure value corresponding to the rate is calculated. Fuzzy inference is performed in the fuzzy inference means 4 based on the chromaticity value of this object and the membership function stored in the memory 2,
A correction value for the reference reflectance corresponding to the reflectance estimated from the chromaticity value is output. The rule used here is the rule excluding the two-manpower related to the illumination light source from the four-manpower one output rule described in the first embodiment. Rules are selected by designation using the light designation charter vessel 87 or light bulb light designation button 88.

In other words, when the button 86 for specifying a clear sky or shadow light is pressed, the rules R1 to R7 for illumination light sources with the two-person power removed are used, and similarly, the sunlight specification charter boat 87 or the electric bulb light specification button 87 is used. When button 88 is pressed, rule R
2 regarding the illumination light source of 8 to R14 or R15 to R21
Perform fuzzy inference using something that removes human power.

Based on the correction value obtained as a result and the exposure value corresponding to the reference reflectance calculated in advance, the calculation control unit 3'
A correction calculation is performed in , and a correct exposure value is calculated. Based on the correct exposure value calculated by this correction calculation, the exposure value is displayed on the display section 5, and the exposure control section 6 performs automatic exposure.

According to the light meter of the second embodiment as described above, the specification information of the illumination light source can be manually inputted, so the user's experience can be utilized, and compared to the first embodiment, it is easier to memorize membership functions. The amount of memory required can be reduced, fuzzy inference becomes easier, and a coloring section dedicated to the illumination light source is not required.

Next, a third embodiment of the present invention will be described with reference to FIGS. 8 and 9. The exposure meter shown in FIG. 8 is different from the exposure sub-unit shown in FIG. The difference is that it is possible to specify the colorimetric operation of the illumination light source to the arithmetic and control unit 3'', and the rest is the same, so the same reference numerals as in FIG. 6 are given.

FIG. 9 shows an example of the cross-sectional structure of the exposure meter shown in FIG. 8, and compared to the exposure meter shown in FIG. The difference is that the light designation button 88 is omitted and the colorimetry mode designation button 89 of the illumination light source colorimetry mode designation device 72 is provided. ing.

In the exposure meter of the third embodiment as described above, at the time of measurement, first, the chromaticity value of the illumination light source is set to 41 by pressing the embellishment mode designation button 89, and the measurement result is stored in the memory 2. With this configuration, it becomes possible to automatically specify the illumination light source, and it can be used as a substitute for the illumination light source specifying device 71 in the second embodiment.

After this, the photometry start button 8 is pressed as in the second embodiment.
When you perform photometry by pressing 5, photoelectric conversion and A/D
The conversion is performed, and the arithmetic control unit calculates an exposure value corresponding to the chromaticity of the subject, the brightness, and the reference reflectance based on the brightness. Based on the chromaticity value of the object and the membership function stored in the memory 2, fuzzy inference is performed in the fuzzy inference means 4, and the reference reflectance corresponding to the reflectance estimated from the chromaticity value is A correction value is output.

According to the exposure meter of the third embodiment as described above, it is possible to automatically specify the illumination light source without providing the 71111 color section dedicated to the illumination light source as in the second embodiment.

Note that in the second and third embodiments, it is also possible to change the fuzzy inference rules and the inference method, and for the color system, the RBG system and other methods can be considered. Further, the exposure meter of the second embodiment and the exposure meter of the third embodiment may be attached to the camera.

Furthermore, in each of the above embodiments, the fuzzy inference means may be replaced by an arithmetic control section. In addition to using a filter and a light-receiving element, the color embellishing means can also be achieved by combining a prism, a diffraction grating, and a light-receiving element.

[Effects of the Invention] As detailed above, according to the light meter of the present invention, the light from the subject is separated into basic color components, instead of having the reflectance of the subject uniformly set to 18% as in the conventional case. By measuring the chromaticity and correcting the exposure value based on the relationship between the chromaticity stored in memory and the reflectance of the subject, a remarkable effect is achieved in that the correct exposure value can always be output. Ru.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a first embodiment of the exposure meter of the present invention, Fig. 2 is a diagram showing an example of the arrangement when the exposure meter of Fig. 1 is applied to a camera, and Fig. 3 is a CIE 2 degree field of view. XY
Spectral stimulus values X(λ), y(λ) in Z display system
, 2(λ); FIG. 4 is a diagram showing the membership functions stored in memory; FIG.
The figure shows the distribution of correction values based on chromaticity and subject reflectance in the orthogonal coordinate system of chromaticity coordinates X and y using rule R8 in Figure 4.
- Chromaticity diagram shown for R14, Fig. 6 is a block diagram showing a second embodiment of the exposure meter of the present invention, Fig. 7 is a diagram schematically showing the cross-sectional structure of the exposure meter of Fig. 6, Fig. 8 9 is a block diagram showing a third embodiment of the exposure meter of the present invention, FIG. 9 is a diagram schematically showing the cross-sectional structure of the exposure meter of FIG. 8, and FIG. 10 is a diagram explaining the outline of fuzzy inference. . F] ~F, ... Wavelength selective filter, P, ~F. ...Photodetector for colorimetry, E1-E6...Photoelectric conversion circuit, H1-H,, J...Sample hold circuit, 81-
S1゜...Selection switch, ]...A/D conversion circuit, 2
...Memory, 3.3', 3"...Arithmetic control unit, 4.
... Fuzzy inference means, 5. Display section, 6. Exposure control section.

Claims (1)

[Scope of Claims] A photometric means for measuring the brightness of a subject, a colorimetric means for measuring the chromaticity of the subject, and a reflectance of the subject is estimated by fuzzy inference from the chromaticity of the subject measured by the colorimetric means. and a correction means for correcting a difference from a reference reflectance to an exposure amount based on the output of the photometering means.