JP3109095B2 - Photometric device using charge storage type photoelectric conversion means - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a charge accumulation type in which a photometric value is obtained by using a photoelectric conversion output and a charge accumulation time of a commonly used integration type photoelectric conversion element in an autofocus camera or the like. The present invention relates to a photometric device using photoelectric conversion means, and enables a highly accurate photometric value to be obtained in a short time under a flicker light source such as a fluorescent lamp.

2. Description of the Related Art Conventionally, in an autofocus camera or the like, when an attempt is made to obtain a photometric value related to subject brightness from an output of a focus detection device composed of a commonly used integrating photoelectric conversion element, a flicker such as a fluorescent lamp is used. Under some light sources, the photometric value calculated depending on whether the charge is accumulated at the position of the flicker peak or at the position of the valley has an error with respect to the average subject brightness, so that the photometric accuracy may decrease. Are known.

In Japanese Patent Application Laid-Open Nos. 62-19824 and 62-259022, during a plurality of integration operations, a charge accumulation time determined by a real-time monitor (hereinafter, this method is referred to as a hard AGC and is determined by this method) It is disclosed that an average value of the charge accumulation time is referred to as a hard AGC time) is used to remove the influence of a photometric value change every time, and to obtain an accurate photometric value with respect to average subject luminance.

In addition, in a focus detection device composed of an integral type photoelectric conversion element, in order to determine the charge accumulation time, a method of determining the charge accumulation time based on the output obtained in the previous accumulation (hereinafter, this method is called soft AGC and And the charge accumulation time determined by this method is referred to as a soft AGC time).

The device driven by the soft AGC is a suitable method because the output can be set to an optimum level by calculation regardless of the luminance distribution of the subject.

[Problems to be solved by the invention] However, when driven by soft AGC,
The charge storage output may be saturated due to the influence of flicker of the light source. That is, if charge accumulation is performed in the valley portion of flicker at the time of the previous accumulation, charge accumulation is performed in a state darker than the average state, and the next time (that is, this time) However, the storage time of ()) is set longer according to the dark state. However, if the current time is not the flicker valley as in the previous case, the accumulated charge becomes too large, and as a result, a part (bright part) or all of the charge accumulation output is saturated.

If the charge storage output is saturated, no information on how bright the saturated portion was can be obtained, and it is not desirable to obtain a photometric value with such a device.

In the above disclosed example driven by the hard AGC time, the monitor element (usually a silicon photodiode) for controlling the charge accumulation time of the focus detection device in real time is usually a pixel element group of the device in which it is used. Since the light receiving area is much smaller than the above, using only the hard AGC time determined from the output of the monitor element as the subject brightness information means that the brightness of a very small part is measured, and stability is also taken into consideration. There is a problem in photometric accuracy.

In addition, regardless of the AGC method, usually one integration operation requires an A / D conversion time of about 20 to 50 ms and a focus detection calculation time in addition to the charge accumulation time and the transfer time. In order to improve the photometric accuracy, it is necessary to perform multiple measurements (Japanese Patent Laid-Open
It is necessary to wait for the end of the integration operation (four times in the disclosed example of 22), which sacrifices the quick shooting performance of a camera using these devices.

The present invention has been made in view of such a conventional problem, and particularly with respect to a device driven by a soft AGC, photometry is performed in a relatively short time with high accuracy and without saturation even under a flicker light source such as a fluorescent lamp. The value is obtained.

[Means for Solving the Problems] In order to solve such problems, a first aspect of the present invention is a charge driven by an auto gain control method in which a current charge accumulation time is determined by an output obtained from a previous charge accumulation. Storage type photoelectric conversion means, real-time monitoring means for monitoring the amount of light incident on the photoelectric conversion means during the charge storage time of the photoelectric conversion means, and time required for the output of the real-time monitoring means to reach a predetermined threshold value. Counting means for counting, storage means for storing a value counted by the counting means, a count value for the previous charge accumulation stored in the storage means, a count value for the current charge accumulation by the counting means, The current charge accumulation time and a value obtained by sequentially A / D converting the output of each pixel of the photoelectric conversion means in the current charge accumulation. Computing means for calculating the subject brightness by using the calculation means.

According to a second aspect of the present invention, the arithmetic means calculates the current charge accumulation based on the integrated value of the value obtained by sequentially A / D converting the output of each pixel of the photoelectric conversion means in the current charge accumulation and the current charge accumulation time. Calculating the subject brightness by calculating the subject brightness at the time, and correcting the subject brightness at the time of the current charge accumulation with the count value related to the previous charge accumulation and the count value related to the current charge accumulation. I do.

According to a third aspect of the present invention, in particular, the interval between the start of the previous charge accumulation and the start of the current charge accumulation is substantially n / 2 times (n is an odd number) of the flicker cycle of the light source. It is characterized by.

According to a fourth aspect of the present invention, the time required for the output of the real-time monitoring means to reach a predetermined threshold value under the constant light is a predetermined ratio more than the charge accumulation time of the photoelectric conversion means under the constant light. It was a short time.

[Operation] The current charge accumulation time is determined by the photoelectric conversion means based on the output obtained from the previous charge accumulation, and the incident light amount is monitored in real time during the charge accumulation time of the photoelectric conversion means by the real-time monitoring means. The time until the output of the real-time monitoring means reaches a predetermined threshold value is counted by the means, the value counted by the counting means is stored by the storage means, and the previous count value stored by the storage means The subject brightness is calculated using the count value, the current charge accumulation time, and the value obtained by sequentially A / D converting the output of each pixel this time.

In particular, after the start of the first integration operation, the second integration is started after a lapse of a time substantially n / 2 times (n is an odd number) of the predetermined flicker cycle of the light source, and the first hard AGC time And the second hard AGC time is used as a correction value to obtain an accurate photometric value for the average subject luminance from the subject luminance value obtained by the second integration operation.

Embodiment FIG. 1 is a configuration diagram showing one embodiment of the present invention. This utilizes some of the functions of known focus detection devices,
The present application has no direct relationship with the focus detection device. In FIG. 1, 1 is a photographing lens, 2 is a film equivalent surface, 3a and 3b are re-imaging lenses, 4a and 4b are photoelectric conversion element groups, 5 is an element driving circuit, 6 is a photoelectric conversion means, and 7 is a photometric operation. Means 8 is a storage means.

The photoelectric conversion means 6 converts the image of a certain area on the film equivalent surface 2 by the re-imaging lenses 3a and 3b into photoelectric conversion element groups 4a and 4b.
Each is re-imaged on top. In the focused state, the photoelectric conversion element groups 4a and 4b are configured to measure light in the same area.

FIG. 2 shows the structure of the photoelectric conversion means 6 shown in FIG. 1, and the photoelectric conversion means 6 comprises the photoelectric conversion unit 4 and the element driving circuit 5. The photoelectric conversion unit 4 includes elements P1 to Pn
Become more photosensor arrays 4 _1, photosensor array 4 ₁
Composed from initialization (reset) integrating clearing circuit 4 _2, shift gate 4 ₃ for transferring the accumulated charge stored in the photo sensor array 4 ₁ from element R1 CCD shift register 4 ₄ consists of Rn. Element driving circuit 5, the luminance monitoring element 5 ₁ arranged in the vicinity of the photosensor array 4 _1, brightness monitor circuit 5 _2, video signal output circuit 5 _3, interface circuit ₄ is composed of a reference voltage generating circuit 5 ₅ ing. Among them, the photo sensor array 4 ₁ of the central portion right is used as a symbol 4b of FIG. 1, so that the left side is used as a symbol 4a. Although brightness monitor light-receiving element 5 ₁ is the same length as the photosensor array 4 _1, the area is configured extremely small.

Hereinafter, the driving operation of the photoelectric conversion unit 6 according to the present invention will be described. First, the first integration operation is performed. Here, the first time refers to a certain integration operation for convenience, and is not an operation at the beginning of operation.

Although from the interface circuit ₄ to the accumulation clear circuit 4 ₂ accumulation clear signal 4 ₅ sent, after its termination, each photosensor in the photosensor array 4 ₁ starts charge accumulation at a speed corresponding to the object luminance . Hard AGC time and the output signal 5 ₆ of brightness monitor circuit 5 ₂ based on the photocurrent _5-7 brightness monitor light-receiving element 5 ₁ is determined by the reference voltage 5 ₈ of the reference voltage generating circuit 5 _5.

After completion of the integration clear signal 4 _5, the photocurrent _5-7 brightness monitor light-receiving element 5 ₁ output signal 5 ₆ of brightness monitor circuit 5 ₂ according to the subject brightness, so when bright rapidly, when it is dark slowly voltage It is designed to descend. Interface circuit 5 ₄ and the output signal 5 ₆ of brightness monitor circuit 5 _2, reference voltage by comparing the reference voltage 5 ₈ which is the output of the generator 5 _5, outputs the hard AGC time signal 5 ₁₁ when it becomes the same potential I do.

Hard AGC time signal 5 ₁₁ is supplied to the photometric calculation means 7, a hard AG from the end of the integration clear signal 4 ₅ via an interface circuit 5 ₄ is also supplied to the photometric calculation means 7
C time signal 5 and ₇ counted photometry calculation means 7 is a time until the occurrence of, in the storage unit 8 as the first hard AGC time.

On the other hand, the integration operation is completed by the soft AGC calculated by the photometric calculation means 7.

Photometric calculation means 7 counts up the current software AGC time that was predetermined by the integration clear signal 4 ₅ end pixel output obtained from previous accumulation from the soft AGC time signal when it reaches the soft AGC time send to the interface circuit 5 _4. Interface circuit 5 ₄ software
The AGC time signal input, sends a shift pulse 4 ₆ to the shift gate 4 _3.

The input of the shift pulse 4 _6, the photosensor array 4 ₁
Accumulated charge is transferred to the CCD shift register 4 _4. After that, the transfer pulse φ1 generated by the interface circuit 5 _4,
And this phase is based on the video signal 5 ₉ obtained by 180 degrees different transfer pulse .phi.2, correction processing pixel signals
5 ₁₀ is output from the video signal output circuit 5 _3.

This signal is supplied to the photometric calculation unit 7 via an interface circuit 5 _4, where it is one by one A / D converter, and stores the resulting value in the storage means 8. The photometric calculation means 7 calculates the next soft AGC time from the obtained pixel output,
Prepare for the second integration operation.

After the transfer of the CCD shift register 4 _4, (1/2 of the time of preferably flicker cycle) a predetermined time from the first integrating operation start entering the second round of the integration operation after elapse. The operation is the same thereafter, and the photometric calculation means 7 stores the obtained data in the storage means 8. The second pixel output is also stored in the storage unit 8.

FIG. 3 is a diagram collectively showing the above operations. First
The second charge accumulation time is t10, the first hard AGC time is t1, the second hard AGC time is t2, the start time difference between the first integration operation and the second integration operation is td, This shows a case where the luminance of the subject during the second charge accumulation operation is twice as high as the luminance of the subject during the first charge accumulation operation.

The second hard AGC time t2 is equal to the first hard A
It is 1/2 of GC time t1. The first hard AGC time, the second hard AGC time, the second charge accumulation time, and the A / D conversion of each pixel signal are sequentially performed in the second integration operation stored in the storage unit 8. Using the obtained value, an accurate photometric value for the average subject luminance is obtained.

Hereinafter, details of obtaining a photometric value using the above information will be described. Here, first, an arithmetic expression for obtaining a photometric value from the output of the focus detection device constituted by the integrating photoelectric conversion element is shown as follows.

B = A × S / T (1) B: subject brightness A: constant S: pixel output integrated value T: integration time FIG. 4 is a diagram showing an integration operation under a flicker light source. Hereinafter, description will be made with reference to FIG.

As in FIG. 3, if the second charge accumulation time is t20 and the integrated value of the value obtained by A / D converting the output of each pixel by the second integration is S2, the second method of obtaining the subject luminance is as follows.
The subject brightness B2 at the time of the second integration is obtained by the following equation.

B2 = A × S2 / T20 (2) The subject luminance in the second integration operation may be higher or lower than the average state due to the influence of flicker. The value of B2 calculated by equation (2) is not always the exact average subject luminance. Assuming that the hard AGC time when the object luminance is average is tA, the start time of the first integration operation and the start time of the second integration operation are almost an odd multiple of 1/2 of the flicker cycle of the light source. Because of the predetermined time difference (= td) as the interval, the hard AGC time tA in the state where the geometric mean of the first hard AGC time t1 and the second hard AGC time t2 is an average state
And the following equation is obtained.

tA = SQRT (t1 × t2) (3) Here, focusing on the second hard AGC time t2,
Compared to the average state, the subject brightness during the second integration operation is short when the brightness is high, and long when the brightness is low.

As described above, the luminance value when the subject brightness is average is BA, the hard AGC time when the subject brightness is average is tA, the subject brightness during the second integration is B2, and the second integration is B2. Assuming that the hard AGC time is t2, the following equation holds between them.

BA × tA = B2 × t2 (4) By transforming this equation and substituting equations (3) and (2), the following equation is obtained.

BA = A × (S2 / t20) × {t2 / SQRT (t1 × t2)} (5) As described above, according to the present invention, accurate integration with respect to the average object brightness can be achieved by performing the integration operation twice during the operation of the apparatus. A photometric value can be obtained. Further, the number of parameters used for the operation is relatively small, and the memory used is small.

FIG. 5 shows an example of the algorithm for calculating the photometric value described above. First, the process starts in step P1, and the hard AGC time t2 is counted in step P2. After the integration operation is completed, the output of each pixel obtained by this integration is A / D in step P3.
The integrated value S2 of the converted value is calculated.

Next, in step P4, the previous hard AGC time t1 stored in the storage means is inputted, and in step P5, the present soft AGC time t20 which is also predetermined from the previous accumulation result is inputted.

Next, in step P6, the photometric value BA is calculated using the above equation (5), and the operation ends in step P7. Metering value is Hard AG
As a correction coefficient using the C time information, a value obtained by A / D conversion of each pixel output (in this case, an integrated value) is used, and as described above, photometry is performed by the light receiving unit of the photoelectric conversion element group. That is, the photometric accuracy is good.

Further, in the present apparatus, the photoelectric conversion means is assumed to be driven by soft AGC, but the charge accumulation condition can be quickly optimized by the real-time monitoring means for a sudden change in the luminance of the subject. In other words, under the condition of steady light,
When the hard AGC time is adjusted to be a predetermined ratio short time (for example, 1/2) of the soft AGC time, it is much earlier than 1/2 of the soft AGC time calculated from the previous charge accumulation result. If the hard AGC time is reached at the time (for example, before the soft AGC time x 1/4), there is a high possibility that the brightness of the subject has become twice or more the previous time, so the time when the hard AGC time x 2 is reached If the charge accumulation is stopped without waiting for the completion of the soft AGC time, the danger of saturation of the output after photoelectric conversion can be avoided.

In the opposite case, that is, when the hard AGC time does not reach the completion time of the soft AGC time, there is a high possibility that the subject luminance has become 1/2 or less of the previous time. If the charge accumulation is terminated when the hard AGC time is reached, the danger of extremely low output can be avoided.

FIG. 6 is a diagram for explaining this application example. The hard AGC reference signal (SHHR), which changes at a time equal to the soft AGC time × 1 after the photometric calculation means starts charge accumulation, and changes at the time of the soft AGC time t20. Table 1 shows an algorithm for calculating the input timing of the soft AGC time signal (SHS) using the soft AGC time reference signal (SHSR) and the hard AGC time signal (SHH).

When the control of the apparatus is changed so as to place emphasis on the hard AGC time as in the above two examples, it is better to allow a certain ratio margin. Because, as described above, the light-receiving element of the real-time monitor of the hard AGC does not necessarily measure the same area as the photoelectric conversion element, and the light-receiving area of the monitor element is small and the output tends to be unstable. Because.

In the above example, a predetermined time ratio is used as a reference when changing the control of the apparatus so that the hard AGC time is emphasized. However, the reference may be changed. That is, the ratio of the soft AGC time to the hard AGC time in the past several charge accumulation operations may be used as a control change reference by the learning function.

Specifically, the hard AGC reference signal (SHH) shown in FIG.
R) The time of change may be adjusted. Further, the driving start of the device, sends a soft AGC time signal (SHS) photometric calculation means after a time lapse of a predetermined multiple of the count value of the hard AGC time to the interface circuit 5 ₄ when the output of the last is not obtained By doing so, the apparatus can be started to drive well.

[Effects of the Invention] As described above, the present invention relates to photometry under a flicker light source such as a fluorescent lamp, which is a problem of a photometer using a conventional integration type photoelectric conversion element, particularly a soft AGC drive. Thus, a highly accurate photometric value can be obtained in a relatively short time.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of the photoelectric conversion means in FIG. 1,
FIG. 3 is a partial wave diagram showing the operation of the photoelectric conversion means, FIG. 4 is a diagram showing an integration operation under a flicker light source, FIG. 5 is a diagram showing an algorithm for photometric value calculation, and FIG. It is a figure showing the example of application of. 1 ... photographic lens, 2 ... film equivalent surface, 3a, 3b ...
Re-imaging lenses, 4a, 4b: photoelectric conversion element group, 5: element driving circuit, 7, photometric calculation means, 8: storage means.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI H04N 5/335 G03B 3/00 A

Claims (4)

(57) [Claims] 1. A charge storage type photoelectric conversion means driven by an auto gain control method for determining a current charge storage time based on an output obtained from a previous charge storage; Real-time monitoring means for monitoring the amount of light incident on the photoelectric conversion means, counting means for counting the time until the output of the real-time monitoring means reaches a predetermined threshold value, and storage means for storing the value counted by the counting means A count value for the previous charge accumulation stored in the storage means, a count value for the current charge accumulation by the counting means, the current charge accumulation time, and each of the photoelectric conversion means in the current charge accumulation. Each pixel output
A photometric device using charge storage type photoelectric conversion means, comprising: arithmetic means for calculating subject brightness using the A / D converted value. 2. The method according to claim 1, wherein the calculating means calculates a current charge accumulation time based on an integrated value of values obtained by sequentially A / D converting outputs of the respective pixels of the photoelectric conversion means in the current charge accumulation and the current charge accumulation time. And calculating the subject brightness by correcting the subject brightness at the time of the current charge accumulation with the count value related to the previous charge accumulation and the count value related to the current charge accumulation. A photometric device using the charge storage type photoelectric conversion unit according to claim 1. 3. An interval according to claim 1, wherein the interval between the start of the previous charge accumulation and the start of the current charge accumulation is substantially n / 2 times (n is an odd number) of the flicker cycle of the light source. A photometric device using a charge storage type photoelectric conversion unit, characterized in that: 4. The photoelectric conversion device according to claim 1, wherein the time required for the output of the real-time monitor to reach a predetermined threshold under the constant light is equal to the time required for the photoelectric conversion under the constant light. A photometric device using charge storage type photoelectric conversion means, wherein the charge storage time is shorter by a predetermined ratio than the charge storage time.