JPH02213285A - Exposure controller - Google Patents

Abstract

PURPOSE:To obtain the video output of a fixed level with high color reproducibility by determining the peak wavelength of a spectral sensitivity characteristic in a photometric optical system including a photometry element and the peak wavelength of the spectral sensitivity characteristic in an image pickup optical system including an image pickup element by an optical correcting means so as to be almost coincident. CONSTITUTION:The thickness of a first IR (infrared) cut filter 11 is set so that the peak wavelength of the spectral sensitivity characteristic to the objective light of the image pickup optical system including a CCD 1 can be made equal with the peak wavelength of the spectral sensitivity characteristic to the objective light of the photometric optical system including a photometry element Si-PD 7. When the peak wavelength is made coincident like the above mentioned processing, fluctuation to a color temperature change can be almost effectively suppressed even in case there is slight difference in the shape of the spectral sensitivity characteristic. Accordingly, even when exposure quantity is controlled in correspondence to the the brightness of an object, to which photometry is executed by the photometric system, the exposure quantity by a CCD 3 is not changed by the color temperature change. Thus, regardless of the change in the color temperature of an object lighting source, the level of the video output can be fixed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an exposure control device for a camera that can obtain a captured image signal with good color reproducibility regardless of the color temperature of a light source.

[Prior Art] Recently, electronic cameras have been developed that electronically image a subject using a solid-state image sensor such as a CCD, electronically record the captured image signal, and provide the image for playback on a TV monitor or the like. Various types have been developed. Among them, electronic still cameras, which capture the subject image as an electronic still image and record it on a floppy disk, memory card, etc., are easier to reproduce captured images (image playback), transmit photos, etc. than so-called silver halide cameras. It is attracting attention because of its excellent handling properties.

Incidentally, in this type of electronic still camera, the amount of light on the image plane of the subject imaged through the imaging lens optical system is adjusted according to the brightness (luminance) of the subject, which is also the case with silver halide cameras. need to be controlled. That is, the image plane light amount of the subject on the imaging surface of a CCD commonly used as an image sensor is adjusted to a level corresponding to the photographing shutter speed at that time, and the exposure jl (exposure amount) is adjusted to - is necessary.

In order to perform such exposure amount control, conventionally, the brightness (luminance) of the subject is generally measured using a photometric element such as a silicon photodiode (Sl-PD), and the imaging lens is adjusted according to the measured value. The amount of light on the object image plane on the imaging plane is adjusted by controlling an aperture diaphragm mechanism or the like built into the optical system.

However, S f- used as such a photometric element
The spectral sensitivity characteristics of PD have a peak around 900 nm, for example, as illustrated in FIG. 4, and are significantly different from human visibility. Therefore, conventionally, the 1lF
An IR (Infrared) cut filter is inserted into the J-light optical system to correct the a11 photosensitivity characteristic due to the Si-PD so that it equivalently has a peak around 550 ns. In other words, the brightness (luminance) of the subject is measured using spectral sensitivity characteristics that approximate human visual sensitivity. According to the brightness (luminance) of the subject measured under such conditions, the image plane light amount of the subject that is imaged on the imaging plane of the CCD is adjusted.

On the other hand, an image sensor (such as a CCD) that electronically captures a subject image with the image surface light amount adjusted in this way has a structure in which many minute pixels (light receiving units) are arranged in a matrix, and extremely fine captured images can be captured. There is a trend toward increasing the number of pixels due to the demand for more and more pixels. However, as the number of pixels increases, the spectral sensitivity characteristics of CCDs show a tendency for their peak wavelengths to shift to shorter wavelengths compared to the aforementioned Sl-PD. Most of the spectral sensitivity characteristics have a peak around 500 nII, as shown in FIG. 5, for example. However, there are several problems with the color reproducibility of images captured by CCDs with such spectral sensitivity characteristics, and it has generally been necessary to improve the color reproducibility. I am trying to insert a cut filter.

[Problems to be Solved by the Invention] However, the spectral sensitivity characteristics of the all light system corrected by the above-mentioned IR cut filter are those that match the spectral sensitivity characteristics to human visibility; Since the spectral sensitivity characteristics of the imaging system that are corrected by the cut filter are designed to improve color reproducibility, there are some differences in these spectral sensitivity characteristics. For this reason, if the color temperature of the illumination light source for the subject changes, the exposure amount control for the imaging probe will change accordingly, so the video output will be within a range of ±10%, for example, as shown in Figure 6. There was a problem that it fluctuated. In order to correct such fluctuations in video output, a method of controlling the exposure amount according to the color temperature of the object illumination light measured by a white balance (WB) sensor, etc., has been proposed, for example, in Japanese Patent Laid-Open No.
Although this method has been proposed in Japanese Patent No. 3-70232, etc., it has problems such as its exposure control system being extremely complicated.

The present invention has been made in consideration of these circumstances, and its purpose is to provide stable color reproduction with good color reproducibility without complicating exposure control and without being concerned with the color temperature of illumination light. An object of the present invention is to provide an exposure control device that makes it possible to obtain an electronically captured image.

[Means for Solving the Problems] The present invention relates to an exposure control device in a camera that electronically images a subject using an image sensor, and includes a photometer including a 7111 optical element for measuring the brightness (luminance) of the subject. optical correction means for making the peak wavelength of the spectral sensitivity characteristic of the optical system coincide with the peak wavelength of the spectral sensitivity characteristic of the imaging optical system including an image pickup element for electronically capturing an image of the subject;
For example, it is characterized by comprising an optical correction means provided to correct the spectral sensitivity characteristics of the photometric optical system with respect to the fixedly determined spectral sensitivity characteristics of the imaging optical system.

[Function] According to the present invention, the optical correction means causes the peak wavelength of the spectral sensitivity characteristic of the n1 light optical system including the photometric element to substantially match the peak wavelength of the spectral sensitivity characteristic of the imaging optical system including the image sensor. Therefore, after making the spectral sensitivity characteristics of the photometric optical system almost match human visual sensitivity and correcting the spectral sensitivity characteristics of the imaging optical system to improve color reproducibility, Since the exposure amount is controlled in accordance with the color temperature of the light source, it is possible to obtain a constant level of video output with high color reproducibility from the image sensor regardless of changes in the color temperature of the light source.

[Example] Hereinafter, an exposure control apparatus according to an example of the present invention will be described with reference to the drawings.

1 and 2 are diagrams showing the schematic configuration of the main parts of the embodiment device, respectively. FIG. 1 shows the first embodiment, and FIG. 2 shows the second embodiment.
An example of this is shown.

In the figure, l denotes an imaging lens optical system, and an aperture diaphragm mechanism 2 for controlling the amount of exposure to a subject is incorporated therein. The imaging surface of a CCD 3, which is an image sensor, is arranged at the focal position of the imaging lens optical system 1, and the subject image formed by the imaging lens optical system 1 is captured by the CCD.
3, the image is electronically captured. Note that the signal of the subject image captured by this CCD 3 is given to the video processor 4, and after being subjected to predetermined signal processing (gamma correction, white balance adjustment, color separation processing, etc.), it is output as a video signal. .

Here, however, a half mirror 5 is disposed in the imaging optical path of the imaging lens optical system 1, and part of the incident light is split laterally. The subject light separated by the half mirror 5 is focused through a condenser lens 6 onto the light receiving surface of a photometric element S1-PD 7, and is used to measure the brightness (luminance) of the subject. This S I-P
The exposure amount control section 8 is driven according to the brightness (luminance) of the subject measured by D 7, and the aperture opening diameter in the aperture diaphragm mechanism 2 is varied according to the photographing shutter speed at that time. The exposure amount for imaging the subject is controlled to be constant.

Here, the first IR cut filter 11 arranged on the light receiving surface of the S i-P D 7, which is a photometric element,
This is a correction so that the spectral sensitivity characteristic for subject light in D7 is equivalently almost equal to the human visual sensitivity.
It consists of an optical glass filter with a predetermined thickness. Also, a second
The IR cut filter 12 is configured to improve the color reproducibility of the subject image electronically captured by the CCD 3.
This is for correcting the spectral sensitivity characteristics of D3 to subject light. The optical low-pass filter 13 disposed in front of the imaging surface of the CCD 3 functions to prevent moire from occurring in the subject image formed on the imaging surface of the CCD 3.

Therefore, the first and second IR cut filters 11 and 12 described above have a characteristic that the transmittance for light components on the infrared light side changes depending on their thickness, as shown in FIG. 3, for example. The thicker the layer, the lower the transmittance of the red component. In other words, the thicker the layer, the more difficult it is to transmit light components on the longer wavelength side. By adjusting the thicknesses of the IR cut filters 11 and 12 using such properties, the CCD 3 and the S
1-The spectral sensitivity characteristics of the PD 7 to the subject light are corrected.

Here, the feature of the present invention is that the thickness of the second IR cut filter 12 inserted into the imaging optical system including the CCDI is adjusted so that the spectral sensitivity characteristics of the CCD 3 to the subject light are adjusted as shown in FIG. A first IR cut filter that is set to a thickness that provides filter characteristics that can be corrected so as to have spectral sensitivity characteristics that can sufficiently ensure color reproducibility, and that is inserted into the photometric optical system including S i-P D 7. The thickness of No. 11 is set to such a thickness that a filter characteristic that can be corrected so that the spectral sensitivity characteristic has the same peak wavelength as the peak wavelength of the spectral sensitivity characteristic with respect to the subject light of the CCD 3 is obtained. It is something. In other words, C
The first R cut is performed so that the peak wavelength of the spectral sensitivity characteristic of the imaging optical system including the CDI to the subject light is equal to the peak wavelength of the spectral sensitivity characteristic of the photometric optical system including the Sl-P D7 to the subject light. This is characterized in that the thickness of the filter 11 is set.

Specifically, when adjusting the spectral sensitivity characteristics of S I-P D 7 to human visibility! The thickness of the R-cut filter 11 is increased to further reduce the sensitivity on the long wavelength side as shown by the dotted line in FIG. Make it equal to the peak wavelength of the overall spectral sensitivity characteristics.

The thickness of the IR cut filter 11 on the 3l-PDT side is determined so that its spectral sensitivity characteristic is equal to the human visual sensitivity, and a short wavelength is set on the CCDa side so that the spectral sensitivity characteristic is equal to the peak wavelength of the human eye. It is also conceivable to insert a filter that reduces side components and correct the spectral sensitivity characteristics as shown by the dashed line in FIG. However, in this case, the object light that is imaged on the imaging surface of the CCD 3 is completely cut off, so the former is preferable when considering the minimum illuminance of the object imaged by the CCD 3.

Therefore, as mentioned above, it is more advantageous to correct the spectral sensitivity characteristics on the S i-P D 7 side, but rather, when considering the minimum subject illuminance, the spectral sensitivity characteristics on the S i-P D T side should be corrected. It can be said that.

In addition, while changing the spectral sensitivity characteristics on the CCDa side,
It is also possible to correct the spectral sensitivity characteristics on the I-PD 7 side so that their peak wavelengths match. In this case,
Not only can the peak wavelength be matched, but the shape of the spectral sensitivity characteristic itself can also be made similar to the product, so it is most effective when capturing only the fluctuation of video output with respect to color temperature. It can be said that this is an effective correction method.

However, from a practical point of view, even if the shapes of the spectral sensitivity characteristics are not made to be similar, if the peak wavelengths match, even if there is a slight difference in the shape of the spectral sensitivity characteristics, there will be almost no change in response to changes in color temperature. As mentioned above, the spectral sensitivity characteristics of the photometric optical system can be corrected while the spectral sensitivity characteristics of the imaging optical system are fixedly corrected to ensure color reproducibility. It can be said that it is more convenient to do so.

By the way, as mentioned above, when correcting the peak wavelength of the spectral sensitivity characteristic in the photometric optical system to be equal to the peak wavelength of the spectral sensitivity characteristic of the imaging optical system, this causes the first
It is undeniable that the thickness of the IR cut filter 11 becomes thicker. Therefore, in order to eliminate such a problem, the position where the second IR cut filter 12 is provided is determined in front of the 71-fmirror 5 as shown in FIG. It is desirable to also have the function of correcting the spectral sensitivity characteristics for.

If such an arrangement structure is adopted, S I-P D 7
The first IR cut filter 11 placed in front of the
Since it is sufficient to have filter characteristics sufficient to compensate for the insufficient correction of the spectral sensitivity characteristics in the photometric optical system that is corrected by the second IR cut filter 12, the thickness should be reduced accordingly. becomes possible. That is, in this case, the amount of IR cut filter inserted into the photometric optical system is the sum of the first and second IR cut filters 11°12. Therefore, compared to the embodiment shown in FIG. 1, the amount of filter required for the first IR cut filter 11 is reduced, and the thickness thereof can be reduced accordingly. As a result, effects such as being able to reduce the weight of the electronic camera can be achieved.

Incidentally, by coating the half mirror 5 described above with a vapor-deposited interference filter, the half mirror 5 itself has an I.
It is also possible to provide R-cut filter characteristics. Even in this case, by determining the spectral sensitivity characteristics of the imaging optical system and the all-ordinary optical system to the subject light as described above, the same effects as in the above-described embodiments can be achieved.

As explained above, according to the present invention, the spectral sensitivity characteristics for the subject light in the 711+1 light optical system and the spectral sensitivity characteristics for the subject light in the imaging optical system are determined so that their peak wavelengths are equal. , Even if the exposure amount is controlled according to the brightness of the subject measured with a 1-light system,
Since the amount of exposure from the CCD 3 does not change depending on the color temperature, it has great practical effects such as making it possible to keep the video output level constant regardless of changes in the color temperature of the object illumination light source. It will be done.

Note that the present invention is not limited to the embodiments described above. For example, as shown in FIG.
In the case where an IR power filter is provided independently in each of the 7 and 7, it is similarly applicable to the case where an external Dj destination method is adopted without adopting the TTL photometry method as shown in this figure. Also, as an IR cut filter,
Usually, a glass filter having predetermined filter characteristics is used, but it is of course possible to use other optical filter elements. In addition, the present invention can be implemented with various modifications without departing from the gist thereof.

[Effects of the Invention] As explained above, according to the present invention, the peak wavelength of the spectral sensitivity characteristic for the subject light in the imaging optical system and the spectral sensitivity characteristic for the subject light in the i>1 light optical system can be adjusted by optical correction means. Because they match, the exposure amount can be easily and effectively controlled without complicated exposure control, and a constant video output can be obtained regardless of the color temperature of the subject light. A great practical effect can be achieved.

[Brief explanation of the drawing]

1 and 2 are schematic configuration diagrams of main parts showing different embodiments of an exposure control device according to the present invention, and FIG. 3 is an IR
Figure 4 shows the spectral sensitivity characteristics of 5t-PD as an N1 optical element and its corrected spectral sensitivity characteristics. Figure 5 shows the spectral sensitivity of CCD as an image sensor. A diagram showing characteristics and their corrected spectral sensitivity characteristics, and FIG. 6 is a diagram showing variations in video output with respect to color temperature in a conventional device. DESCRIPTION OF SYMBOLS 1... Imaging lens optical system, 2... Aperture diaphragm mechanism, 3... CCD (image sensor), 4... Video processor, 5... Half mirror 6... Condensing lens,
7...5i-PD ('6pJ optical element), 8...Exposure control section, 11...First! R cut filter, 12.
...Second IR cut filter. Applicant's agent Patent attorney Jun Tsuboi District 1 Figure 4 Figure 5 Figure 3

Claims (2)

[Claims] (1) In a camera that electronically images a subject using an image sensor, the peak wavelength of the spectral sensitivity characteristic of the photometric optical system including the photometric element, and the peak wavelength of the spectral sensitivity characteristic of the imaging optical system including the image sensor. An exposure control device characterized by comprising an optical correction means for substantially matching the values. (2) The optical correction means is provided to correct the spectral sensitivity characteristics of the photometric optical system with respect to the fixedly determined spectral sensitivity characteristics of the imaging optical system. exposure control device.