JP2000358190A - Exposure control circuit of image input device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exposure control circuit of an image input device which sets the incident light quantity, an exposure time and the number of addition via a condition setting circuit according to the detected luminance of an object in order to set a proper state with the dynamic range and luminance of the object and in response to the intention of a photographer. SOLUTION: The object light whose incident light quantity is controlled via a diaphragm 16 is electronically photographed and inputted by a CCD image pickup element 18, and the image signals which are read with the element 18 are added together in plural times by a cumulative addition circuit 25. The luminance of an object is detected with a luminance detector 33 and a condition setting circuit 31 sets the incident light quantity, an exposure time and the number of addition according to the detected luminance. Thus, the quantity of light set by the diaphragm 16, the exposure time of the element 18 and the cumulated number of addition of the circuit 25 are controlled and the object is picked up in most proper state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image input apparatus such as an electronic camera using cumulative addition, and more particularly, to an exposure control circuit of an image input apparatus which speeds up imaging of a subject having a wide dynamic range.

[0002]

2. Description of the Related Art In recent years, various solid-state imaging devices such as a CCD image sensor and a MOS image sensor have been developed. The development of an image input device such as an electronic camera that electronically captures an image of a subject using these solid-state imaging devices has been developed.
Various activities have been performed.

The dynamic range of a subject to be imaged by the solid-state imaging device often reaches about 80 dB. Generally, an imaging capability (dynamic range) of a solid-state imaging device is about 50 dB, and it is impossible to image a subject having a wider dynamic range than this. For example, the solid-state imaging device may be saturated in a high-brightness part, causing a so-called overexposed state, or conversely, a low-brightness part may be underexposed, resulting in a so-called black-out state.

To solve such a problem, Japanese Patent Application No. Hei.
No. 34508 discloses an apparatus for accumulating image signals read from a solid-state imaging device to extend a dynamic range. FIG. 23 shows the outline of this device.
FIG. 2 is a schematic configuration diagram of main parts of an electronic camera.

In FIG. 1, an image signal read out at a high speed from a solid-state image sensor (AMI) 1 for electronically capturing and inputting an object (not shown) is amplified to a predetermined signal level via a preamplifier 2. . Thereafter, the signal is subjected to a clipping process or the like in the signal processing circuit 3 and is digitally encoded in the A / D converter 4. Further, the digitally encoded image signal is sequentially stored for each frame via an adder 5 in a frame memory 6 for performing cumulative addition in combination with the adder 5.

[0006] In the video signal, the luminance signal component Y is separated and extracted in the video processor 7 from the image signal whose dynamic range is expanded by the cumulative addition.
It is decomposed into three primary color components of R, G and B. Luminance signal component Y
Is a log amplifier 8a in the dynamic range control circuit 8.
Is logarithmically converted to log Y and taken in. And
The signal from which the uneven illuminance component has been removed via the two-dimensional filter 8b is input to a dynamic range gain controller (DGC) 8c. Here, after an output in which the dynamic range of the luminance signal component Y is adjusted to the dynamic range of the image monitor is obtained, the output is output from the log amplifier 8a to the adder 8e together with the output via the delay circuit 8d. Thus, the compression coefficient of the dynamic range is obtained.

On the other hand, the three primary color components R, G and B converted and output by the video processor 7
logR, logG, logB via r, 9g, 9b
After the logarithmic conversion, the delay circuits 10r, 10g, 1
0b are supplied to adders 11r, 11g, and 11b, respectively. And these adders 11r, 11g,
At 11b, the above-mentioned compression coefficient is added, and after being subjected to inverse logarithmic conversion by the inverse log amplifiers 12r, 12g, and 12b, D / D
Through the A converters 13r, 13g, and 13b, a signal component having a compressed dynamic range is obtained.

[0008] The apparatus having such a configuration utilizes the fact that random noise is reduced by cumulative addition, thereby making it possible to obtain a wide dynamic range.

[0009]

However, in the above-described apparatus according to the prior art, the relationship between the cumulative number of additions by the solid-state imaging device and the exposure time is not described in detail. Here, assuming that the cumulative addition number is n, the signal value is n times and the noise value is n ^1/2 times, so that the imaging dynamic range can be n ^1/2 times.

[0010] That is, i) the dynamic range can be widened as the number of additions increases, but the time spent for imaging increases. ii) Unnecessary cumulative addition is performed when the dynamic range of the subject to be imaged is narrow, and the imaging time becomes unnecessarily long. iii) When imaging a high-luminance subject, the exposure time of the solid-state imaging device must be shortened. Conversely, when imaging a low-luminance subject, the exposure time must be increased. As described above, the cumulative addition number and the exposure time need to be set to appropriate states in accordance with the dynamic range and luminance of the subject to be imaged.

The present invention has been made in view of the above points, and an image input apparatus capable of setting a most appropriate state according to a photographer's intention based on a dynamic range and luminance of a subject to be imaged. It is an object of the present invention to provide an exposure control circuit.

[0012]

According to a first aspect of the present invention, there is provided a solid-state image pickup device for picking up an image of a subject and converting the image into an electric image signal, and reading out the image signal of the picked-up object from the solid-state image pickup device. Means, and an exposure control circuit of an image input device comprising: a cumulative addition means for cumulatively adding the image signals read from the solid-state image sensor. Light amount adjusting means for adjusting; solid-state image sensor control means for controlling the time during which the subject is exposed on the solid-state image sensor for imaging; and a cumulative addition number of image signals in the cumulative addition means. Cumulative addition number control means for controlling, subject brightness detection means for detecting an upper limit value and a lower limit value of the brightness of the subject, and outputting corresponding signals as a brightness upper limit value signal and a brightness lower limit value signal; Based on the dynamic range of the subject determined from the signal and the luminance lower limit signal, optimal numerical values are set for the incident light amount, the exposure time, and the cumulative addition number, and the respective numerical values are used as control signals. And a condition setting means for outputting to the light quantity adjusting means, the solid-state imaging device control means and the cumulative addition number control means.

According to a second aspect of the present invention, there is provided a solid-state imaging device for imaging an object and converting the image signal into an electric image signal, means for reading out the image signal of the imaged object from the solid-state imaging device, An exposure control circuit of an image input apparatus comprising: an accumulating means for accumulating the image signal read from the element; and a light amount adjusting means for adjusting an incident light amount incident on the solid-state imaging element from the subject. A solid-state image sensor control means for controlling a time during which the subject is exposed on the solid-state image sensor for imaging; and a cumulative addition number control for controlling the cumulative number of image signals in the cumulative addition means. Means for storing fixed pattern noise of the solid-state imaging device, and a fixed pattern stored in the storage means from the image signal before converting the image signal into a format compatible with an external device. Subtraction means for subtracting an image noise, an object luminance detection means for detecting an upper limit value and a lower limit value of the luminance of the subject, and outputting a corresponding signal as a luminance upper limit value signal and a luminance lower limit value signal; Based on the dynamic range of the subject determined from the luminance lower limit signal, an optimal numerical value is set for the incident light amount, the exposure time, and the cumulative addition number, and each numerical value is used as a control signal, and the corresponding light amount adjusting means is set. Condition setting means for outputting to the solid-state image sensor control means and the cumulative addition number control means,
It is characterized by having.

In the exposure control circuit of the image input apparatus according to the present invention, the object is imaged by the solid-state image sensor and converted into an electric image signal, and the image signal of the imaged object is output from the solid-state image sensor. Is read. Then, the image signals read from the solid-state imaging device are cumulatively added by the cumulative addition means. Further, the amount of light incident on the solid-state imaging device from the subject is adjusted by a light-amount adjusting unit, and the time during which the subject is exposed on the solid-state imaging device for imaging is controlled by the solid-state imaging device control unit. You.
The cumulative addition number of the image signal in the cumulative addition means is controlled by the cumulative addition number control means, and the upper limit value and the lower limit value of the brightness of the subject are detected by the subject brightness detection means. It is output as an upper limit signal and a lower luminance signal. Then, in the condition setting means, optimal values are set for the incident light amount, the exposure time, and the cumulative addition number, based on the dynamic range of the subject determined from the luminance upper limit signal and the luminance lower limit signal. The respective numerical values are output as control signals to the corresponding light amount adjusting means, solid-state image sensor control means, and cumulative addition number control means.

In the exposure control circuit of the image input apparatus according to the present invention, the object is imaged by a solid-state image sensor and converted into an electric image signal, and the image signal of the imaged object is converted into the solid-state image signal. Read from the image sensor. Then, the image signals read from the solid-state imaging device are cumulatively added by the cumulative addition means. The amount of light incident on the solid-state imaging device from the subject is adjusted by a light-amount adjusting unit, and the time during which the subject is exposed on the solid-state imaging device for imaging is controlled by the solid-state imaging device control unit. Controlled. Further, the cumulative addition number of the image signal in the cumulative addition means is controlled by the cumulative addition number control means, and the fixed pattern noise of the solid-state imaging device is stored in the storage means. Then, before converting the image signal into a format compatible with an external device, the fixed pattern noise stored in the storage unit is subtracted from the image signal by a subtraction unit. The upper limit value and the lower limit value of the brightness of the subject are detected by the subject brightness detection means, and corresponding signals are output as a brightness upper limit signal and a brightness lower limit signal. Then, based on the dynamic range of the subject determined from the luminance upper limit value signal and the luminance lower limit value signal, optimal values for the incident light amount, the exposure time, and the cumulative addition number are set in the condition setting means. Are output as control signals to the corresponding light amount adjusting means, solid-state image sensor control means, and cumulative addition number control means.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic block diagram showing an entire electronic camera to which an exposure control circuit of an image input apparatus according to the present invention is applied. In FIG. 1, reference numeral 14 denotes a photographing optical system. The amount of incident light from the optical system 14 via the half mirror 15 is adjusted by a stop 16. The aperture value F of the aperture 16 is controlled by an F-number control circuit 17.

The input image that has passed through the aperture 16 is electronically picked up by a CCD image pickup device 18 having random noise of the nature described below. The CCD image pickup device 18 includes a CCD
The drive circuit 19 controls the reading and exposure time T. The image signal output from the CCD imaging device 18 is amplified to a predetermined signal level via a preamplifier 20, and subjected to a clipping process or the like in a signal processing circuit 21. Thereafter, the image signal digitally encoded by the A / D converter 22 is output to the subtractor 23, where the FPN of the CCD image sensor 18 stored in the fixed pattern noise (FPN) storage ROM 24 in advance is removed. .

The image signal from which the FPN has been removed by the subtractor 23 is supplied to an adder 26 constituting a cumulative addition circuit 25. Then, the output of the adder 26 is sent to the frame memory 27, and is sequentially stored for each frame. The cumulative addition circuit 25 controls the cumulative addition number by a cumulative addition number control circuit 28. The signal Sn cumulatively added by the cumulative addition circuit 25 is subjected to processing such as luminance conversion and encoding by the image processing circuit 29,
Thereafter, the data is written on the recording medium 30.

The F value control circuit 17 and the CCD drive circuit 1
The 9 and the cumulative addition number control circuit 28 are respectively controlled by a condition setting circuit 31 composed of, for example, a microprocessor. The condition setting circuit 31 converts a part of the subject light into a half mirror 15 and a total reflection mirror 32 to be imaged.
Based on the maximum luminance Lh and the minimum luminance Ll of the subject detected by the luminance detector 33 derived through the aperture 16.
, The exposure time T of the CCD image sensor 18, and the cumulative addition number n of the cumulative addition circuit 24.

FIG. 2 shows the details of the condition setting circuit 31 of FIG. 1. The maximum luminance Lh and the minimum luminance Ll of the subject supplied by the luminance detector 33 are respectively input to a dynamic range detection circuit 311. You. The dynamic range detection circuit 311 provides an S / N ratio snl of the subject having the minimum luminance Ll set by the S / N setting circuit 312.
From (dB), the maximum luminance Lh, and the minimum luminance Ll, a dynamic range DR of imaging is detected. Then, the dynamic range DR detected by the dynamic range detection circuit 311 is output to the nT condition setting circuit 313,
Here, to determine the cumulative addition number n and the exposure time T, n,
Constraint I for T is calculated and is outputted as a condition C _I in the parameter setting circuit 314.

The maximum luminance Lh is output to the FT condition detection circuit 315, where the constraint value II for the F value and the exposure time T is calculated and output to the parameter setting circuit 314 as the condition C _II . The FT condition detection circuit 315 outputs a state signal C _FT (described in detail later) under the conditions of F and T to the parameter setting circuit 314.

To the parameter setting circuit 314, for example, a mode signal mode set as follows from the imaging mode setting circuit 316 is output. Mode 1: The imaging time is set to the shortest. Mode 2: Make the imaging time constant. Mode 3: Make the depth of field the deepest. Then, the parameter setting circuit 314 compares the mode signal mode thus set with the above-mentioned conditions C _I , C _II
And the state signal C _FT to calculate and set the most appropriate aperture value F, exposure time T, and cumulative addition number n.

FIG. 3 shows the details of the luminance detector 33 shown in FIG. 1. The incident light of the subject led out through the half mirror 15 and the total reflection mirror 32 is applied to a line driven by a drive circuit 331. Non-destructive sensor 3 composed of sensors
4 is incident. Then, the image signal SO electronically read by the non-destructive sensor 34 is amplified by the preamplifier 332, digitally encoded by the A / D converter 333, and input to the luminance calculator 334. Further, the peak value signal PE is output from the non-destructive sensor 34 to the luminance calculator 334.
Is input to The output of the luminance calculator 334 is supplied to the counter 335 together with the drive circuit. Further, the brightness calculator 334 outputs the output from the A / D converter 333,
The maximum luminance Lh and the minimum luminance Ll are calculated from the peak value signal PE and the count number Cnt from the counter 335.

FIG. 4 shows the structure of the non-destructive sensor 34 shown in FIG.
_1, ..., it has a 341 _n. These photosensors 341 _1, ..., the 341 _n, the read switch 342, respectively _1, ..., the scanning circuit 343 through 342 _n are connected. The driving of the scanning circuit 343 causes the read image signal to be output as an image signal SO from the terminal 345 via the output amplifier 344. 346 is a reset switch.

[0026] In addition, the photo sensor 341 _1, ..., 341
_n is a buffer amplifier 347 ₁ ,.
_The peak detector 348 is connected via _n . The peak value is detected from the peak detector 348 and output from the terminal 349 as a peak value signal PE.

Next, the noise of the solid-state imaging device will be described.

There are various types of noise in the solid-state image sensor.
These are mainly divided into the two noises mentioned above, namely fixed pattern noise (FPN) and random noise.
Among random noise (N _R) is an image signal can be relatively reduced by cumulative addition. In addition, the random noise, dark current noise which depends on the exposure time (N _D), in which is divided into an exposure time-independent system noise (N _S), these two types of noise, shown in FIG. 5, for example To change.

Now, the cumulative addition number is n, and the exposure of the solid-state image sensor is
When the light time is T and the exposure time T is cumulatively added n times
Think about the noise. Then, at the time of total exposure in this case
Interval t _BIs represented by nT. Dark current without cumulative addition
Noise N_DIs represented as Equation 1.

[0030]

(Equation 1) Then, when the cumulative addition is performed n times, it is expressed as in Expression 2.

[0031]

(Equation 2) Further, when the system noise N _S is cumulatively added n times, it is expressed as in Equation 3.

[0032]

(Equation 3) Thus the random noise N _R can be expressed as Expression 4.

[0033]

(Equation 4)

If the maximum value of the amplitude of the signal is S, the maximum level of the signal in the case of the cumulative addition number n is nS.
It is represented as

[0035]

(Equation 5) Here, only random noise will be considered.

FIG. 6 shows the above equation 5 in a graph. In the figure, both the vertical axis and the horizontal axis are expressed by logarithms, and are expressed by the relationship shown in Expression 6.

[0037]

(Equation 6)

From FIG. 6, it is possible to know the exposure time and the number of cumulative additions for obtaining the required dynamic range.

In order to obtain a certain dynamic range, a plurality of combinations of the exposure time T and the cumulative addition number n can be considered. However, the exposure time T is determined by the brightness of the subject and the F number of the photographing optical system. That is, assuming that the maximum luminance of a subject that can be imaged without being saturated is _Lmax , it is expressed by the relational expression of Expression 7.

[0040]

(Equation 7)

Here, k is a constant determined depending on the sensitivity of the image pickup device. On the other hand, if the minimum luminance that can be imaged is L _min , it is expressed by the relational expression of Expression 8.

[0042]

(Equation 8)

Here, L _min is a noise level. The DR in the above equation 8 is the DR (n, T) in the above equation 5
That is.

Here, the luminance of the object to be imaged is changed from the minimum luminance Ll [cd / m ² ] to Lh [cd / m ² ] (where L
1 <Lh). At this time, assuming that the dynamic range of the subject is dr, Expression 9 is obtained.

[0045]

(Equation 9)

The imaging dynamic range DR required to secure snl [dB] as the S / N ratio of the minimum luminance L1 is expressed by Expression 10.

[0047]

(Equation 10)

In this case, the S / N of the object having the maximum luminance Lh
The ratio is DR [dB]. Then, as a condition for imaging without saturating the maximum luminance Lh, the relational expression of Expression 11 is required.

[0049]

[Equation 11]

From this, the exposure times T and F numbers that satisfy Expression 12 are selected by combining Expressions 11 and 7 above, and the cumulative addition number n may be obtained from Expression 5 above.

[0051]

(Equation 12) Next, the operation of the embodiment will be described.

When the image pickup is started, first, the luminance detector 33
Thus, the maximum luminance Lh and the minimum luminance Ll of the image of the subject to be imaged are obtained. That is, referring to FIG. 3, when the luminance detection is started, the non-destructive sensor 34 is reset and the counter 335 is set to zero. Next, when the exposure of the non-destructive sensor 34 is started, the counter 335 starts counting along with the exposure. Then, as shown in FIG. 7, assuming that the peak value signal PE reaches the saturation value after the time t ₀ seconds, the maximum luminance Lh is obtained from the count number Cnt _{0 at} that time.

At this time, the minimum value of the image signal gives the minimum luminance. If the minimum value is lower than the noise level determined by the S / N ratio of the non-destructive sensor 34, the exposure is further increased. Continue. Then, the signal is read out at every predetermined time (for example, time t ₁ , t ₂ ,...), And the time when the minimum luminance Ll exceeds the above noise level (time t _{3 in the} figure)
Is obtained from the count number (Cnt _{3 in} this case).

By performing such an operation, the dynamic range dr of the subject becomes smaller than the S / S of the nondestructive sensor 34.
Even when the ratio is larger than the N ratio, the maximum luminance Lh and the minimum luminance Ll can be accurately obtained.

In this way, the maximum luminance L
h and the minimum luminance Ll are obtained, these luminances L
h and Ll are supplied to the dynamic range detection circuit 311 in the condition setting circuit 31. In the dynamic range detection circuit 311, first, the dynamic range dr of the subject is calculated based on Equation 9 described above. Next, the dynamic range dr of this subject and the S / N setting circuit 3
S / N required by the subject with the minimum brightness set in 12
From the ratio snl, the dynamic range DR required for imaging
Is obtained from the above equation (10). nT condition detection circuit 313
In response to the dynamic range DR, and calculates the constraint I represented by the equation number 13 from the number 5, and outputs the condition C _I in the parameter setting circuit 314.

[0056]

(Equation 13)

On the other hand, the FT condition setting circuit 315 secures the dynamic range DR of imaging and obtains the condition II expressed by the relational expression of Expression 14 for imaging the subject having the maximum luminance Lh.
Is calculated, and the parameter setting circuit 31 is used as the condition C _II.
4 is output.

[0058]

[Equation 14]

FIGS. 8A and 8B show conditions C
_It shows examples of _I and C _II . Here, FIG.
And the hatched portion of the dynamic range DR is larger than view at (a), the portion represented by the solid line Lh In FIG (b) is a portion that satisfies the condition C _I and C _II, respectively.
Therefore, the cumulative addition number n, the aperture value F, and the exposure time T that satisfy these need only be set. A plurality of combinations of these three parameter values are possible, and it is necessary to select the most appropriate value.

Now, it is assumed that the exposure time T can be changed continuously within the range of T _{min to} T _max , and the cumulative addition number n is 1 to
Takes an integer value of n _max , and the aperture value F is F _{min to} F
_It is assumed that continuous values can be taken until _close (zero incident light quantity).

Here, as shown by (i) in FIG. 9B, when the value of the maximum luminance Lh satisfies the relationship of Lh ₁ <Lh,
The exposure time T is in the range of T _min ≦ T ≦ T _max ,
The aperture value F is in the range of F ₁ ≦ F ≦ F ₁ ′. Similarly, as shown in (ii), the value of the maximum luminance Lh is Lh ₂ ≦ L
When h ≦ Lh ₁ , the exposure time T falls within the range of T ₂ ≦ T ≦ T _max , and the aperture value F falls within the range of F _min ≦ F ≦ F ₂ ′. Furthermore, as shown in (iii), if the value of the maximum luminance Lh is Lh of <Lh _2, T satisfying the above condition C _II, F will not be present. And (i),
Each of the states (ii) and (iii) is transmitted from the FT condition detection circuit 315 to the parameter setting circuit 3 as the state signal CFT described above.
14 is output.

The condition C shown in FIG._IITo
Thus, the condition C shown in FIG. _IHorizontal axis (T)
Is determined. For example, in the case of the above (i) (T_min≤T≤T
_max), The imaging dynamic range DR is the maximum DR₁of
The exposure time T = T_maxin the case of
Is at most DR_ThreeIs possible up to. In the case of (ii) above
(T_Two≤T≤T_max), Imaging dynamic range D
R is a portion indicated by oblique lines in FIG. And
When the cumulative addition number n at this time is maximized, T = T_TwoNoto
Up to DR_TwoGet the dynamic range of imaging up to
be able to.

FIGS. 10A to 10C show the condition C
It is a conceptual diagram illustrating the dynamic range or the like in accordance with _I and C _II. FIG. 11A shows a case where both the conditions C _I and C _II are satisfied, FIG. 10B shows a case where only the condition C _II is satisfied, and FIG. 9C shows a case where the condition C _I is satisfied. If not,
It is each conceptual diagram. In each of the figures, the vertical axis corresponds to luminance, and DR ₁ shown here is:
The maximum dynamic range that can be obtained in each state.

In FIG. 10A, the dynamic range DR covers a wide range from _NR to Lh. In the case of FIG. 10B, the maximum luminance value that can be imaged does not change unless F and T are changed. In this case, D-1: S / N
Changes snl to snl ', D-2: secures snl without taking the high luminance side, D-3: D-1 and D-2 above
Between the two can be selected. In the case of the D-2, Lh 'shall be at least of the value F _min ² k / T _max. Further, in the case of FIG.
D-4: Dynamic range of imaging is shown from DR to D
R-5, D-5: S / N changes from snl to snl '.

The following mode settings are made according to the shooting mode. Mode A: The cumulative addition number n is made as small as possible. Mode B: The cumulative addition number is set to a constant value (n _C ). Mode C: The aperture value F is made as large as possible, and n is made as small as possible to shorten the imaging time.

Based on the above, the most appropriate n, F, and T are set for each state and each mode as shown in the relation diagram of FIG. Note that, here, examples of the above-described states (i) and (ii) in which three parameters of n, F, and T can be set by a plurality of combinations are shown.

According to this principle, in the present embodiment, the condition setting circuit 31 sets the most appropriate cumulative addition number n and aperture value F in accordance with the dynamic range, luminance, and desired imaging mode of the subject. , An exposure time T is set. Then, based on these parameters, the cumulative addition circuit 25 performs cumulative addition. Also, FPN storage ROM
The FPN of the CCD imaging device 18 is calculated by the
Is obtained and the signals are cumulatively added, so that the signal Sn obtained from the cumulative addition circuit 25 does not include FPN. Therefore, it is possible to obtain a signal having the dynamic range shown in the above equation (5). Further, the signal Sn is generated by the image processing circuit 29.
Processing such as luminance conversion and encoding as proposed in Japanese Patent Application Laid-Open No. 63-232591 is performed, and is written on the recording medium 30.

In this embodiment, the minimum value of the aperture value F is assumed to be F _min and cannot be made smaller than this value. May be supplemented.

In the embodiment, the subject light is directly guided to the luminance detector for image pickup using a half mirror or the like. However, the present invention is not limited to this. For example, a separate finder system is used. It is also possible.

Further, although three types of image pickup modes are set, priority is given to making the depth of field shallow,
The priority may be given to shortening the exposure time T.

The maximum luminance value Lh and the minimum luminance value Ll
May be one point in the image or an average value of a plurality of points.

Since the magnitude of the dark current noise greatly changes depending on the temperature, a temperature sensor is provided.
A more accurate dark current noise may be detected.
Further, the imaging device may be cooled to suppress dark current noise, and a wider dynamic range may be obtained.

Further, the condition setting circuit shown in FIG.
RO that inputs h, Ll, and snl and outputs n, F, and T
M can also be used.

Next, a second embodiment of the present invention will be described with reference to FIGS. In addition, the first
The same parts as those of the first embodiment are denoted by the same reference numerals, and description thereof will be omitted to avoid duplication.

FIG. 12 is a schematic block diagram showing the whole of an electronic camera to which the exposure control circuit of the image input device is applied according to the second embodiment of the present invention. , A subject brightness detector 35 is provided. FIG. 13 shows details of the subject brightness detector 35. The subject indicator 351 is composed of, for example, a finder and a button. When this button is depressed, an image of a subject on the optical axis of the photographing optical system 14 that is visible at the center of the finder is taken, and the luminance thereof is calculated by the luminance calculator 334
Is output from Here, the brightness calculator 334 outputs the maximum brightness Lh ′ and the average value Lave ′ of the signal to the subject brightness calculator 352 using the signal when the peak value is saturated. This subject brightness calculator 352
Based on the maximum luminance Lh 'and the average value Lave', the maximum luminance Lh of the image to be picked up and the average luminance Lave of the subject are detected.

Here, the subject brightness calculator 352 comprehensively determines the brightness of a plurality of subjects specified by the subject indicator 351 and determines the maximum brightness Lh and the average brightness L of the subjects.
Output ave. For example, assuming that j types of subjects are designated, Lh _i , L h _i , and L _i , L _{h i} , (i = 1 to j), Lh, L a are obtained from the relational expression expressed by Expression 15.

[0077]

(Equation 15) Next, the operation of the second embodiment will be described.

Now, consider a case where the outside of a window is photographed from inside a room as shown in FIG. 14, for example. Assume that the brightness of each subject indicated by p, q, r, and s in the drawing is as follows. Landscape outside the p window Lh ₁ , Lave ₁ q Light Lh ₂ , Lave ₂ r Bookshelf Lh ₃ , Lave ₃ s Clock Lh ₄ , Lave _4, and maximum brightness value when each subject is sequentially designated by the subject indicator 351 Lh and the average value Lave are represented as in the conceptual diagram of FIG.

The Lh and Lave calculated by the object luminance calculator 352 are output to the condition setting circuit 31. Next, processing is performed in the same manner as in the first embodiment described above, and parameters are set in place of Lave instead of Ll. Here, when the dynamic range of the imaging of DR> DR _1, as shown in FIG. 10 (b), as giving priority to the low luminance side S / N, in the figure D
As shown by -2, the dynamic range of imaging is set. In this way, by ensuring the S / N ratio of Lave, the subject (main subject) that is most desired to be photographed can be obtained.
Can be satisfactorily captured.

In the second embodiment, as shown in FIG. 15, Love is the average value Lav of the bookshelf r and the clock s.
The luminance value is larger than e ₃ and Love ₄ , and the required S / N ratio is not necessarily ensured for these two subjects. In this case, the subject indicator 351
In this case, the subject may be specified a plurality of times. For example,
Once on the scenery p outside the window, once on the light q, twice on the bookshelf r,
Specify clock s four times. Then, the maximum luminance and the average luminance become Lh 'and Lave' in FIG. 15, and the S / N ratio of the bookshelf and the timepiece is also ensured.

As described above, according to the present embodiment, by specifying the image to be captured, the parameters n, F, and T are set so that the main subject can be captured best, and the image is captured. .

In the above-described second embodiment, a line sensor is used for the subject luminance detector 35. However, if an area sensor is used, the subject can be specified without moving the photographing optical system.

Further, the luminance calculator 334 detects the maximum luminance value Lh 'and the average value Lave' of the subject. However, the present invention is not limited to this, and the minimum luminance value is calculated in the same manner as in the first embodiment. After detection, the parameters n, F, and T may be set in consideration of the minimum luminance.

In the first and second embodiments described above,
The half mirror 15 and the total reflection mirror 32 are provided to obtain the brightness of the subject. However, the use of such a member generally has a disadvantage that the optical system becomes large and the entire device becomes large. Therefore, an embodiment that does not use the above members will be described next.

In FIG. 16, reference numeral 36 denotes a pre-photometric circuit, which is a circuit that replaces the luminance detector 33 of the first embodiment and the subject luminance detector 35 of the second embodiment. It receives the output signal of the A / D converter 22 as an input and outputs the maximum value Lh and the minimum value Ll of the signal to the condition setting circuit 31.

As a different part from the first and second embodiments, an image sensor capable of high-speed reading, in this case, a CMD (Charge Modulatio) is used instead of the CCD image sensor 18.
n Device) 18a and a CMD drive circuit 19a. Further, the output of the image processing circuit 29 is input to the monitor 37. Other configurations are the same as those of the above-described first and second embodiments, and a description thereof will be omitted.

Next, the operation of the third embodiment will be described. The signal picked up by the CMD 18a is read out at a high speed, A / D converted, and
Is input to The pre-photometering circuit 36 detects the maximum value Lh and the minimum value Ll of the input signal,
Output to the condition setting circuit 31.

The condition setting circuit 31 determines whether or not the signal of the maximum value Lh is saturated. When the signal is saturated, the exposure time T is shortened or the aperture value is increased. . On the other hand, if it is not saturated, the exposure time T is lengthened or the aperture value is reduced. This operation is performed every time a signal is read from the CMD 18a, so that the CMD adjusted to the relational expression represented by Expression 16 is obtained.
Since the high-speed reading is performed from 18a, the time required for this adjustment is very short.

[0089]

(Equation 16)

At this time, the dynamic range dr [dB] of the subject is determined from the above equation 9 from the minimum value Ll of the read signal. When detecting Lh and Ll, nondestructive reading may be performed many times during one exposure, as in the luminance detector 33 of the first embodiment.

In this embodiment, the maximum value Lh,
The unit of the minimum value Ll is a value as luminance after A / D conversion, and is different from the unit [cd / m ² ] used in the above-described first and second embodiments. is there.

Then, the dynamic range DR of imaging is obtained from the above equation (10). Hereinafter, the exposure time T, the aperture value F, and the cumulative addition number n are set in the same manner as in the first and second embodiments.

As described above, the exposure time T, the aperture value F, and the cumulative addition number n are set, and the signal S of the cumulative addition number is set.
The image signal processing circuit 29 performs a luminance conversion process on n, and outputs the result to the monitor 37.

In this embodiment, since a high-luminance image pickup device is used, the time required for the cumulative addition number n can be made equal to or less than one frame time of NTSC. The image having a wide dynamic range can be observed by the monitor 37 without causing unnatural movement.

Further, in this embodiment, since a pre-photometric circuit for performing photometry from the read signal is provided, a member for separating the optical path of the optical system is not required. Therefore, it is possible to reduce the size of the entire device.

Since the CMD is also capable of random access, the time required for setting conditions can be further reduced by limiting the reading position at the time of pre-metering to a small area to be imaged.

Next, a fourth embodiment of the present invention for detecting the FPN to be subtracted for each image pickup will be described.

It is known that FPN has a high temperature dependency and its value greatly differs depending on the use environment. Also,
Even if used at the same temperature due to clock noise, etc., FP
N may change. As the cumulative addition number n increases, the FPN also increases in proportion to n. Therefore, it is very important to accurately subtract only the FPN in order to obtain a wide dynamic range. Therefore, in the fourth embodiment, FPN is stored at the time of imaging, so that accurate FPN subtraction is performed.

FIG. 17 is a block diagram showing the whole of an electronic camera to which the exposure control circuit of the image input device is applied. In the figure, different from the first embodiment described above, a mechanical shutter 38 is provided immediately before the CCD image pickup device 18, and a shutter control device 39 and an FPN storage changeover switch 40 are further provided. The shutter 38 is
It may be inserted inside the optical system 14. still,
The other parts are the same as those in the above-described embodiment, and thus the same reference numerals are given and the description will be omitted.

Next, the operation of the fourth embodiment will be described. When the imaging is started, the shutter controller 39 is controlled by a controller (not shown), and the shutter 38 is closed. At the same time that the light is blocked by the shutter 38, the FPN storage switch 40 is set to a
It is switched to the side. The signal read after exposure for one frame time is A / D converted and stored in the FPN storage ROM 24. Then, in the next frame, the shutter 38 is opened, the subject light from the optical system 14 is focused on the CCD image pickup device 18, and the FPN storage switch 40 is switched to the b side. Thus,
Imaging is performed in the same manner as in the first embodiment described above.

As described above, immediately before the imaging is performed, the FPN
Is stored, accurate FPN subtraction processing can be performed. In the embodiment,
The exposure of the FPN is set to one frame. However, since it is more accurate to use the actual exposure time T, the following may be performed.

That is, even when the shutter 38 is closed and light is shielded, the subject light enters the luminance detector 33. Therefore, the condition setting circuit 31 can be obtained from the outputs Lh and Ll.
In, the exposure time T of imaging, the aperture value F, and the cumulative addition number n are obtained. Then, based on the exposure time T, the CCD image pickup device 18 is exposed, and the read signal is stored in the FPN storage R.
Stored in the OM 24.

In the present embodiment, a signal which is imaged once in a light-shielded state is defined as FPN, but a signal obtained by imaging a plurality of times in a light-shielded state and cumulatively added thereto may be defined as an FPN.

In the above-described embodiment, the image pickup device has C
We use CD, but it is not limited to this,
For example, a CMD (Charge Modulation Device) may be used.

FIG. 18 is a block diagram showing a fifth embodiment of the present invention, and shows an example in which the FPN is detected by the cumulative addition in the third embodiment. is there.

In this embodiment, the output of the accumulator 25 is stored as FPN, and the subtraction process is performed by the multiplier 41 by multiplying the coefficient C _N at the time of imaging. Here, the coefficient C _N is a correction coefficient when the cumulative addition number at the time of storing the FPN is different from the cumulative addition number of imaging. For example, assuming that the cumulative addition number at the time of storing the FPN is N _FPN and the cumulative addition number at the time of imaging is n ′, the relational expression of Expression 17 is established.

[0107]

[Equation 17]

Since the FPN is detected based on the cumulative number, the FPN can be obtained more accurately. In addition, since an image sensor capable of high-speed reading is used, FPN can be detected in a short time.

In the above-described FPN detection in the fourth and fifth embodiments, the shutter 38 is provided so that the subject light is completely shielded. The use of a mechanical shutter increases the size of the entire apparatus. Therefore, without providing such a mechanical shutter, it is conceivable to use a signal captured by shortening the exposure time of the imaging element and increasing the aperture value F as the FPN.

Further, when the maximum value of the aperture value is infinite (∞; aperture value F _close , incident light amount is zero), it is of course possible to use this as a shutter.

Next, referring to FIG. 19, a sixth embodiment of the present invention will be described.
An embodiment will be described. This embodiment uses a solid-state imaging device capable of non-destructive readout to obtain a plurality of images with different exposure times within one exposure period.

The image processing circuit 29 in FIG. 19 is assumed to be a circuit from the video processor circuit 7 in FIG. 23 described in the conventional example to the D / A converters 13 (13b, 13g, 13r).

In the block diagram shown in FIG. 19, a CMD 18a is used as an image sensor capable of nondestructive reading, similarly to the third embodiment. A slice circuit 42 is provided between the subtracter 23 and the accumulator 25, and the slicer 42 is provided between the accumulator 25 and the image processing circuit 2.
The linear conversion circuits 43 are inserted and connected between the terminals 9.

Here, non-destructive reading by the CMD 18a will be described with reference to FIG. In the figure,
At time “0”, a reset (RST in the figure) is executed, and charge accumulation is started. Then, the signal read-out (the READ) is performed when the elapsed time t _1. Then
Signal is read when t ₂ has elapsed. At this time, the read data is a signal that has been exposed during the time t ₁ + t ₂ . In other words, unless a reset operation when a signal is read out at t _1, which indicates that the data is not lost. Signal is read after the t ₂ has elapsed, the accumulated charge reset is performed is eliminated.

As described above, when only reading is performed without performing resetting, a plurality of images having different exposure times can be read during one exposure period.

Next, the operation of this embodiment will be described. The signal from the CMD 18a is supplied to the preamplifier 20.
The signal is then amplified by a signal processing circuit 21 and subjected to processing such as clamping, and is further converted into a digital signal by an A / D converter 22. The FPN is removed from the converted data in the subtractor 23. Then, the images are clipped by the slice circuit 42, and images having different exposure times are sequentially added by the cumulative addition circuit 25. The number of times of addition is set by the condition setting circuit 31.

FIG. 21 is a diagram showing data cumulatively added by the cumulative addition circuit 25. In the figure, shows an example in which the five reading takes place during first exposure period, the longest exposure time of figure f _1, and most short exposure time the f _5, a photoelectric conversion characteristic ing. Since the exposure time is short, the saturation luminance is high.

Now, the photoelectric conversion characteristic outputs of f _{1 to} f ₅ are
It shall sliced by V ₁ at slice circuit 42. Then, the outputs of f _{1 to} f ₅ are added to the cumulative addition circuit 2
By being accumulated and added by 5, the photoelectric conversion characteristics shown in the figure F ₀ is obtained. If non-destructive readout is not performed, for example, only _one light amount represented by L1 in the drawing can be reproduced during one exposure period. However, according to the embodiment, the amount of up to L ₅ far more quantity of light than L ₁ becomes possible imaging.

Since the cumulatively added data is non-linear as indicated by F ₀ , it is converted by the linear conversion circuit 43 into a linear characteristic indicated by F ₁ in FIG. After being converted to a linear signal, the image signal is converted to a signal suitable for the monitor 37 by the image processing circuit 29 and output to the monitor 37.

In the above-described embodiment, the pre-photometering circuit 36 and the like are provided for detecting the luminance. In this embodiment, the video processor 7 of the image processing circuit 29 performs matrix conversion, The luminance signal is detected. The image processing circuit 29 includes a dynamic range gain detection circuit (DGC) 8c shown in FIG.

FIG. 22 shows a circuit configuration of the DGC 8c. Reference numeral 44 denotes a standard deviation generation circuit, which includes an adder 44a,
Square detector 44b, LPF 44c and square root circuit 44d
have. The output of the standard deviation generation circuit 44 is the output of the comparison amplifier 4 having one connected to the variable resistor VR2.
5 and is compared and amplified with a reference voltage. One of the outputs of the comparison amplifier 45 is a variable resistor VR.
4 is supplied to the other input of the changeover switch 46 connected to the switch 4, and automatic control and manual control are switched and selected and output as the dynamic range adjustment voltage β.

The LPF 47 is for calculating the average value of the luminance signal. The output of the LPF 47 is a variable resistor VR1.
Is compared with a gain reference voltage by a comparison amplifier 48 connected to the comparator. Then, by switching the gain setting voltage set by the variable resistor VR3 and the output of the comparison amplifier 48 with the changeover switch 49, automatic control and manual control are switched and selected, and the gain adjustment voltage α is output.

With the DGC 8c having such a configuration, Y
(Luminance signal), signals of α and β can be obtained. The outputs α and β correspond to the average value and the standard deviation of the image at the luminance, respectively. By inputting α and β to the condition setting circuit 31, the aperture and the exposure time are controlled respectively. The operation of the DGC 8c is described in
Since it is described in detail in Japanese Patent Application Laid-Open No. 3-232591, the description is omitted. Further, if the aperture and the exposure time are finely set, the linear processing becomes complicated. Therefore, it is desirable to control the aperture and the exposure time under some predetermined setting conditions. At the time of linear conversion, the above setting conditions are input to the linear conversion circuit 43 via the signal line S, and linear conversion is performed.

By performing the above operations, a plurality of image data can be cumulatively added at high speed, and a wide dynamic range signal can be obtained. Further, in the wide dynamic range signal, since the aperture and the exposure time are optimally set, an image having a good S / N can be obtained.

Although not shown in the embodiment, if the clamp circuit before the A / D converter 22 is unstable, it may be A / D converted and then clamped by the digital section.

As described above, by reading out many times during one exposure period, it is possible to capture an image of a subject having a wider luminance. Further, non-destructive reading may be performed after several exposure periods, not during one exposure period, and reset may be performed after reading this several times.

The color image pickup device used in the present invention is disclosed in Japanese Patent Application Laid-Open No. 63-232591, and Japanese Patent Application No. Hei.
Since it is described in -334508, details are omitted.

[0128]

As described above, according to the present invention, the dynamic range and luminance of a subject to be imaged
It is possible to provide an exposure control circuit of an image input device that can set the most appropriate exposure time, aperture value, and cumulative number according to the photographer's intention.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram showing an entire electronic camera to which an exposure control circuit of an image input apparatus according to the present invention is applied.

FIG. 2 is a block diagram showing details of a condition setting circuit of FIG. 1;

FIG. 3 is a block diagram showing details of a luminance detector of FIG. 1;

FIG. 4 is a circuit configuration diagram showing details of the non-destructive sensor of FIG. 3;

FIG. 5 is a diagram showing a temporal change of random noise.

FIG. 6 is a diagram showing the relationship between the cumulative addition number and the exposure time.

FIG. 7 is a diagram showing a change with time of the accumulated charge amount of the nondestructive sensor.

8 (a) showed a condition C _I corresponding to constraints I calculated in nT condition detection circuit Figure, (b) conditions corresponding to constraints II calculated by FT condition setting circuit C It is the figure which showed _II .

9A and 9B are diagrams showing combinations of parameters of an accumulated addition number, an aperture value, and an exposure time corresponding to the conditions C _I and C _II of FIGS. 8A and 8B, respectively. It is.

[10] (a) ~ (c) is a conceptual diagram illustrating the dynamic range or the like in accordance with the conditions C _I and C _II.

FIG. 11 is a diagram showing the most appropriate parameter relationship between each state in FIG. 9B and the shooting mode.

FIG. 12 is a schematic block diagram showing the entirety of an electronic camera to which an exposure control circuit of an image input device is applied according to a second embodiment of the present invention.

FIG. 13 is a block diagram showing details of a subject luminance detector of FIG. 12;

FIG. 14 is a diagram showing a subject viewed from a finder.

FIG. 15 is a conceptual diagram illustrating a maximum luminance value and an average value of the subject in FIG. 14;

FIG. 16 is a schematic block diagram showing the entirety of an electronic camera to which an exposure control circuit of an image input device is applied according to a third embodiment of the present invention.

FIG. 17 is a schematic block diagram showing the entirety of an electronic camera to which an exposure control circuit of an image input device is applied according to a fourth embodiment of the present invention.

FIG. 18 is a schematic block diagram showing the entirety of an electronic camera to which an exposure control circuit of an image input device is applied according to a fifth embodiment of the present invention.

FIG. 19 is a schematic block diagram showing the entirety of an electronic camera to which an exposure control circuit of an image input device is applied according to a sixth embodiment of the present invention.

20 is a diagram showing the relationship between the amount of charge stored and the exposure time by the electronic camera of FIG.

21 is a diagram illustrating a relationship between an output voltage and a light amount of the electronic camera in FIG.

FIG. 22 is a block diagram illustrating a configuration of a dynamic range gain detection circuit in the image processing circuit.

FIG. 23 is a schematic configuration diagram of a main part of a conventional electronic camera.

[Explanation of symbols]

 Reference Signs List 14 optical system, 15 half mirror, 16 aperture, 17 F value control circuit, 18 CCD image sensor, 19 CCD drive circuit, 20, 332 preamplifier, 21 signal processing circuit, 22, 333 A / D converter, 23 subtractor, 24 Fixed pattern noise (FPN) storage ROM, 25 cumulative addition circuit, 26 adder, 27 frame memory, 28 cumulative addition number control circuit, 29 image processing circuit, 30 recording medium, 31 condition setting circuit, 32 total reflection mirror, 33 Luminance detector, 34 non-destructive sensor, 311 dynamic range detection circuit, 312 S / N setting circuit, 313 nT condition setting circuit, 314 parameter setting circuit, 315 FT condition setting circuit, 316 imaging mode setting circuit, 331 drive circuit, 334 Luminance calculator, 335 counter.

Claims (9)

[Claims] A solid-state imaging device for imaging an object and converting the image signal into an electric image signal; a unit for reading an image signal of the imaged object from the solid-state imaging device; In an exposure control circuit of an image input device including an accumulative addition means for accumulatively adding an image signal, a light amount adjusting means for adjusting an incident light amount incident on the solid-state imaging device from the subject; and Solid-state imaging device control means for controlling the time during which the subject is exposed on the solid-state imaging device; cumulative addition number control means for controlling the cumulative addition number of image signals in the cumulative addition means; An object luminance detecting means for detecting an upper limit value and a lower limit value of the luminance and outputting a corresponding signal as a luminance upper limit signal and a luminance lower limit value signal, and is determined from the luminance upper limit signal and the luminance lower limit signal. Based on the dynamic range of the subject, set an optimal numerical value for the incident light amount, the exposure time and the cumulative addition number, and use each numerical value as a control signal, a corresponding light amount adjusting means, a solid-state image sensor control means, and An exposure control circuit for an image input apparatus, comprising: condition setting means for outputting to a cumulative addition number control means. 2. The photographing mode setting unit, wherein the condition setting means prepares a plurality of conditions for setting the cumulative addition number, and outputs an arbitrary setting condition from the plurality of setting conditions as a mode signal. 2. The image input device according to claim 1, further comprising a parameter setting unit configured to set an optimum numerical value for the incident light amount, the exposure time, and the cumulative addition number based on the dynamic range and the mode signal. Exposure control circuit of the device. 3. The apparatus according to claim 1, wherein said subject luminance detecting means comprises: a solid-state image pickup device capable of nondestructive reading; and peak detecting means for detecting a maximum value of accumulated charges. Exposure control circuit of the image input device according to 1. 4. An object designating means for designating a subject for which the upper and lower limit values of the brightness are to be detected, wherein the subject brightness detecting means sets the upper and lower limits of the brightness of the designated subject. 2. The exposure control circuit according to claim 1, wherein the exposure control circuit calculates and outputs corresponding signals as a luminance upper limit signal and a luminance lower limit signal. 5. The object luminance detecting means includes an area sensor, and based on an output from an area corresponding to the position of the object designated by the object designating means, an upper limit and a lower limit of the luminance of the designated object. 5. The exposure control circuit according to claim 4, wherein the value is calculated and corresponding signals are output as a luminance upper limit signal and a luminance lower limit signal. 6. The subject luminance detecting means detects an upper limit value and a lower limit value of the luminance of the subject based on the image signal read from the solid-state imaging device, and outputs a corresponding signal to a luminance upper limit signal and a luminance value. 2. The exposure control circuit according to claim 1, wherein the signal is output as a lower limit signal. 7. The image input apparatus according to claim 1, wherein the upper limit of the brightness is a maximum brightness of the subject, and the lower limit of the brightness is a minimum brightness or an average brightness of the subject. Exposure control circuit. 8. A solid-state imaging device for imaging a subject and converting the image signal into an electric image signal, means for reading an image signal of the captured subject from the solid-state imaging device, and a device for reading the image signal from the solid-state imaging device. In an exposure control circuit of an image input device including an accumulative addition means for accumulatively adding an image signal, a light amount adjusting means for adjusting an incident light amount incident on the solid-state imaging device from the subject; and Solid-state image sensor control means for controlling the time during which the subject is exposed on the solid-state image sensor; cumulative addition number control means for controlling the cumulative number of image signals in the cumulative addition means; Storage means for storing the fixed pattern noise of the element; and before converting the image signal into a format compatible with an external device,
Subtraction means for subtracting the fixed pattern noise stored in the storage means from the image signal; detecting an upper limit value and a lower limit value of the luminance of the subject; and using corresponding signals as a luminance upper limit signal and a luminance lower limit signal. Based on the subject brightness detection means to be output, and the dynamic range of the subject determined from the brightness upper limit signal and the brightness lower limit signal, optimal values are set for the incident light amount, the exposure time, and the cumulative addition number. ,
An exposure control circuit for an image input device, comprising: a condition setting unit that outputs each numerical value as a control signal to a corresponding light amount adjusting unit, a solid-state imaging device control unit, and a cumulative addition number control unit. 9. The image input apparatus according to claim 4, wherein said subtraction means subtracts the fixed pattern noise stored in said storage means from an image signal output from said image signal reading means. Exposure control circuit.