JP3274692B2 - Exposure control circuit of image input device - Google Patents

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 can speed 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.

Incidentally, the dynamic range of a subject to be imaged by the solid-state imaging device often reaches about 80 dB. Generally, the imaging capability (dynamic range) of a solid-state imaging device is about 50 dB,
It was 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 logarithmically converted into log Y by a log amplifier 8a in the dynamic range control circuit 8 and is taken in. And 2
The signal from which the uneven illuminance component is removed via the 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 are respectively supplied to a log amplifier 9r,
After being logarithmically converted as log R, log G, and log B via 9g and 9b, an adder 1 is provided via delay circuits 10r, 10g and 10b.
1r, 11g, 11b. Then, the compression coefficients are added by these adders 11r, 11g, 11b, and further subjected to inverse logarithmic conversion by the inverse log amplifiers 12r, 12g, 12b, and then passed through the D / A converters 13r, 13g, 13b. Thus, 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. The dynamic range of imaging is n ^1/2 Can be doubled. 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.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and is 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.

[0011]

That is, the present invention provides a solid-state imaging device for imaging a subject and converting it into an electric image signal, a means for reading out the image signal of the captured subject from the solid-state imaging device, An exposure control circuit for an image input device, comprising: an accumulating means for accumulating the image signals read from the solid-state imaging device; a light amount for adjusting an incident light amount incident on the solid-state imaging device from the subject; Adjusting means, for imaging, a solid-state image sensor control means for controlling the time the subject is exposed on the solid-state image sensor,
Cumulative addition number control means for controlling the cumulative addition number of image signals in the cumulative addition means; storage means for storing fixed pattern noise of the solid-state imaging device; and conversion of the image signal into a format compatible with an external device Before performing the subtraction means for subtracting the fixed pattern noise stored in the storage means from the image signal output from the accumulative addition means, detecting an upper limit value and a lower limit value of the luminance of the subject, and detecting a corresponding signal. A luminance upper limit signal and a luminance lower limit signal, and outputs the incident light amount based on a dynamic range of the subject determined from a ratio between the luminance upper limit signal and the luminance lower limit signal. Optimum numerical values are set for the exposure time and the cumulative addition number, and the respective numerical values are used as control signals, and the corresponding light amount adjusting means, solid-state image sensor control means, and cumulative addition A condition setting means for outputting to the control means, characterized by including the. The present invention also provides a solid-state imaging device for imaging a subject and converting the image signal into an electric image signal, a unit for reading an image signal of the captured subject from the solid-state imaging device, In an exposure control circuit of an image input device including a cumulative addition unit that cumulatively adds an image signal, the solid-state imaging device includes:
A solid-state imaging device capable of non-destructively reading the image signal at different times during a period in which the subject is exposed for imaging, and an incident light amount incident on the solid-state imaging device from the subject. A solid-state imaging device control unit for controlling a time during which the subject is exposed for imaging during the exposure period; and a control unit for controlling the cumulative addition number of the image signal in the cumulative addition unit. Means for controlling the cumulative addition number, and converting the cumulatively added data into a linear signal.
A conversion means, and an upper limit value and a lower limit value of the luminance of the subject are determined.
And subject brightness detecting means for outputting a that signal, the subject bright
The upper limit value of the brightness of the subject output from the degree detection means;
Above the brightness of the subject generated from the signal that defines the lower limit
The optimum value for the incident light amount, the exposure time, and the cumulative addition number is determined according to the dynamic range width of the subject determined from the ratio between the limit value and the lower limit value or a condition corresponding to the dynamic range width. A condition setting means for setting and outputting each numerical value as a control signal to a corresponding light quantity adjusting means, a solid-state image sensor control means, and a cumulative addition number control means.

[0012]

In an exposure control circuit of an image input apparatus according to the present invention, a subject is electronically imaged and input by a CCD image sensor through a diaphragm for adjusting the amount of incident light, and the image signals read by the CCD image sensor are cumulatively added. It is added multiple times in the circuit. The brightness of the subject is detected by a brightness detector, and the amount of incident light, the exposure time, and the number of additions are set in a condition setting circuit according to the detected brightness. Accordingly, the amount of light by the aperture, the exposure time of the CCD image pickup device, and the cumulative number of addition of the cumulative addition circuit are controlled, and the subject is imaged in the most appropriate state.

[0013]

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, and the amount of incident light from the optical system 14 via a 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 passing through the aperture 16 is electronically picked up by a CCD image pick-up element 18 having random noise of the nature described below. The reading and exposure time T of the CCD image pickup device 18 is controlled by a CCD drive circuit 19. The image signal output from the CCD image pickup device 18 is amplified to a predetermined signal level via a preamplifier 20, and a signal processing circuit 21 performs a clipping process or the like. Thereafter, the image signal digitally encoded by the A / D converter 22 is output to a subtractor 23, where the CCD signal stored in a fixed pattern noise (FPN) storage ROM 24 in advance is stored.
The FPN of the image sensor 18 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. 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 is controlled by a cumulative addition number control circuit 28. This accumulation circuit
The signal Sn that has been cumulatively added at 25 is subjected to processing such as luminance conversion and encoding by an image processing circuit 29, and then written to a recording medium 30.

The F value control circuit 17, the CCD drive circuit 19, 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 detects the maximum luminance L of the subject when a part of the subject light is detected by the brightness detector 32 derived through the half mirror 15 and the total reflection mirror 32 to be imaged.
Based on h and the minimum luminance Ll, the F value of 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 are controlled.

FIG. 2 shows 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 input to a dynamic range detection circuit 311. You. The dynamic range detection circuit 311 includes an S / N ratio snl (dB) of the subject having the minimum luminance Ll set in the S / N setting circuit 312,
The dynamic range DR of imaging is detected from the maximum luminance Lh and the minimum luminance Ll. The dynamic range DR detected by the dynamic range detection circuit 311
Is output to the nT condition setting circuit 313, where n in order to determine the cumulative addition number n and the exposure time T, constraints I to T is calculated, the parameter setting circuit condition C _I
Output to 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
Then, the state signal C _FT (the details of which will be described later) under the above conditions of F and T is output 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. The parameter setting circuit 314 uses the mode signal mode thus set, the conditions C _I , C _II and the state signal C _FT to determine the most appropriate aperture value F, exposure time T,
The cumulative addition number n is calculated and set.

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

[0022] FIG. 4 shows the configuration of a non-destructive sensor 34 of FIG. 3, a plurality of non-destructive readout photosensors 341 _1,
…, 341 _n . These photo sensors 34
1 ₁ , ..., 341 _n have readout switches 34
2 _1, ..., the scanning circuit 343 through 342 _n are connected. The driving of the scanning circuit 343 causes the read image signal to pass through the output amplifier 344 and from the terminal 345 to the image signal SO.
Is output as Incidentally, reference numeral 346 denotes a reset switch.

Further, the photo sensor 341 _1, ..., the 341 _n, the buffer amplifier 347 _1, respectively, ..., a peak detector 348 via a 347 _n are connected. The peak value is detected from the peak detector 348 and output from the terminal 349 as a peak value signal PE. Next, noise of the above-described solid-state imaging device will be described.

There are various types of noise in the solid-state image pickup device.
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, assuming that the cumulative addition number is n and the exposure time of the solid-state imaging device is T, the noise when the cumulative addition is performed n times with the exposure time T is considered. Then, the total exposure time t _B in this case is represented by nT. Dark current noise N _D when there is no cumulative addition is expressed by the number 1.

[0026]

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

[0027]

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

[0028]

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

[0029]

(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

[0031]

(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.

[0032]

(Equation 6) From FIG. 6, it is possible to know the exposure time and the cumulative addition number 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.

[0034]

(Equation 7) Here, k is a constant determined depending on the sensitivity of the image sensor and the like. 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.

[0035]

(Equation 8) Here, L _min is a noise level. DR of Equation 8 above
Is DR (n, T) in Equation 5 described above.

Here, the luminance of the subject to be imaged is the minimum luminance L1 [cd / m ² ] To Lh [cd / m ² ] (However, Ll <L
h). At this time, assuming that the dynamic range of the subject is dr, Expression 9 is obtained.

[0037]

(Equation 9) Then, as the S / N ratio of the minimum luminance Ll, snl [d
The dynamic range DR of imaging required to secure [B] is expressed as in Expression 10.

[0038]

(Equation 10) In this case, the S / N ratio of the subject having the maximum luminance Lh is DR [d
B]. Then, as a condition for imaging without saturating the maximum luminance Lh, the relational expression of Expression 11 is required.

[0039]

[Equation 11] From this, the above Expression 11 and Expression 7 are combined to obtain Expression 12
May be selected, and the cumulative addition number n may be obtained from the above equation (5).

[0040]

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

When the imaging is started, first, the luminance detector 33 obtains the maximum luminance Lh and the minimum luminance Ll of the image of the subject to be imaged. 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, after the time t ₀ seconds, the peak value signal PE
Has reached the saturation value, the count number Cn at that time
From t ₀ , the maximum luminance Lh is obtained.

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

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

Thus, the maximum luminance Lh is detected by the luminance detector 33.
And the minimum luminance Ll are obtained, these luminances Lh,
Ll is 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 the subject and the S / N ratio sn required by the subject having the minimum luminance set by the S / N setting circuit 312 are set.
From l, the dynamic range DR required for imaging is obtained from the above equation (10). The nT condition detection circuit 313 receives the dynamic range DR, and
Calculating a constraint I represented by the relational expression, and outputs as the condition C _I in the parameter setting circuit 314.

[0045]

(Equation 13)

Meanwhile, the FT condition setting circuit 315, to ensure the dynamic range DR of the imaging, and calculates the condition II represented by the equation number 14 for imaging an object of the maximum luminance Lh, condition C _II Output to the parameter setting circuit 314.

[0047]

[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.

[0049] Now, the exposure time T is T _min through T continuously varies from _max is to be possible, 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),
The states (ii) and (iii) are output from the FT condition detection circuit 315 to the parameter setting circuit 314 as the above-mentioned state signal _CFT .

[0051] Through these conditions indicated C _II in FIG. 9 (b), the horizontal axis of the indicated condition C _I in FIG. 9 (a) (T) is determined. For example, in the case of the above (i) (T _min ≦ T ≦ T
_max), the dynamic range DR of the imaging is possible up to a value of up to DR _1, made possible by up to DR ₃ For these exposure time T = T _max. In the case of the above (ii) (T ₂ ≦ T ≦ T _max ), the dynamic range D of the imaging
R is a portion indicated by oblique lines in FIG. And
If the cumulative addition number n at this time is maximized, a dynamic range of imaging up to DR ₂ can be obtained when T = T ₂ .

FIGS. 10A to 10C show the conditions 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 _II 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 is s
nl changes to snl ', D-2: s without taking high brightness side
nl, D-3: intermediate between the above D-1 and D-2. Here, in the case of D-2, Lh ′ is F _min ² It is assumed that the value is not less than k / _Tmax . Further, in the case of FIG. 10C, D-4: the dynamic range of the imaging is increased from the illustrated DR to DR '.
N can select either snl or 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 such a principle, in the present embodiment, the condition setting circuit 31 sets the most appropriate cumulative addition number n, aperture value F, and aperture value in accordance with each of the dynamic range, luminance, and imaging desired mode of the subject. The exposure time T is set. Then, based on these parameters, the cumulative addition circuit 25 performs cumulative addition. FPN storage ROM 24 and subtractor
23, the signal obtained by subtracting the FPN of the CCD image pickup device 18 is obtained and cumulatively added. Therefore, the signal Sn obtained from the cumulative adding circuit 25 does not include the FPN. Therefore, it is possible to obtain a signal having the dynamic range shown in the above equation (5). Further, the signal S
n is determined by the image processing circuit 29 according to
Processing such as luminance conversion and encoding as proposed in No. 1 is performed, and the data is written to 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. However, appropriate illumination light is turned on to reduce the insufficient light amount. You may make up for it.

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

Further, although three types of setting are set as the imaging mode, priority is given to making the depth of field shallow,
The priority may be given to shortening the exposure time T. Note that 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.
It is also possible to use a ROM in which 1 is an input and n, F, and T are outputs.

Next, a second embodiment of the present invention will be described with reference to FIGS. The same parts as those in the first embodiment are denoted by the same reference numerals, and the 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 apparatus is applied in the second embodiment of the present invention. Instead, a subject brightness detector 35 is provided. FIG.
3 shows the details of the object brightness detector 35.
The subject pointing device 351 includes, for example, a finder and a button. When this button is pressed, an image of a subject on the optical axis of the photographing optical system 14 seen in the center of the finder is taken, and the luminance is output from the luminance calculator 334. Here, the luminance calculator 334 uses the signal at the time when the peak value is saturated, and uses the maximum luminance Lh ′ of the signal.
And the average value Lave 'are output to the subject luminance calculator 352.
The subject luminance calculator 352 calculates the maximum luminance Lh of an image to be captured based on the maximum luminance Lh ′ and the average value Lave ′.
And the average luminance Lave of the subject.

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 Lave of the subjects.
Is output. 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.

[0064]

(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 luminance value when each subject is sequentially designated by 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 brightness 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, the dynamic range of imaging is DR>
For DR _1, as shown in FIG. 10 (b), as to give priority to low-luminance side of the S / N, as shown in the same figure D-2, the dynamic range of imaging is set.
In this way, by ensuring the S / N ratio of Lave, it is possible to satisfactorily photograph the subject (main subject) that is most desired to be photographed.

Incidentally, in this second embodiment, as shown in FIG. 15, Lave is the average Lave of the bookshelf q and the clock r.
_The luminance value is larger than that of ₃ and Love ₄ , and the required S / N ratio is not necessarily ensured for these two subjects. In this case, the subject may be designated a plurality of times by the subject indicator 351. For example, the scenery p outside the window is designated once, the light q is designated once, the bookshelf r is designated twice, and the clock s is designated 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.

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

In the above-described first and second embodiments, 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 member will be described next.

In FIG. 16, reference numeral 36 denotes a pre-photometering 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 and outputs the maximum value Lh and the minimum value Ll of the signal to the condition setting circuit 31.

Further, as a part different from the first and second embodiments, instead of the CCD image sensor 18, an image sensor capable of high-speed reading, here a CMD (Charge Modulation Device) is used.
ce) 18a and the CMD drive circuit 19a are used. 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 captured by the CMD 18a is read at a high speed, A / D converted, and then input to the pre-photometering circuit 36. Then, the pre-photometering circuit 36 detects the maximum value Lh and the minimum value Ll of the input signal and outputs them to the condition setting circuit 31.

The condition setting circuit 31 determines whether or not the signal of the maximum value Lh is saturated. If 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
Or increase the aperture value. This operation is performed every time a signal is read from the CMD 18a, so that CMD 1 is adjusted to the relational expression represented by Expression 16.
Since high-speed reading is performed from 8a, the time required for this adjustment is very short.

[0076]

(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. In detecting Lh and Ll, non-destructive reading may be performed many times during one exposure, similarly to the luminance detector 33 of the first embodiment.

In this embodiment, the units of the maximum value Lh and the minimum value Ll are values as luminance after A / D conversion, and are used in the first and second embodiments. Unit [cd / m ² ].

Then, the dynamic range DR of imaging is obtained from the above equation (10). Thereafter, 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 the 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. With the monitor 37, an image having a wide dynamic range can be observed without 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 description will be given of a fourth embodiment of the present invention in which the FPN to be subtracted is detected for each imaging.

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. Thus, in the fourth embodiment, the 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, unlike the first embodiment described above,
A mechanical shutter 38 is provided immediately before the CCD image pickup device 18, and further includes a shutter control device 39 and an FPN storage changeover switch 40. The shutter 38 may be inserted into the optical system 14. 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 controller (not shown) controls the shutter control device 39 to control the shutter 38.
Is closed. At the same time as the light is blocked by the shutter 38, the FPN storage changeover switch 40 is switched to the a 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 imaged on the CCD image pickup device 18, and the FPN storage changeover switch 40 is switched to the b side. Thus, imaging is performed in the same manner as in the first embodiment.

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

That is, even when the shutter 38 is closed and light is blocked, the subject light is incident on the luminance detector 33. Therefore, from the outputs Lh and Ll, the condition setting circuit 31 uses the exposure time T, The aperture value F and the cumulative addition number n are obtained. Then, based on the exposure time T, the CCD image sensor 18
Is exposed, and the read signal is stored in the FPN storage ROM 24.
Is stored.

Further, in the present embodiment, the signal once photographed in the light-shielded state is defined as FPN. However, a signal obtained by imaging a plurality of times in the light-shielded state and cumulatively added may be used as the FPN. In the above-described embodiment, the CCD is used as the image sensor. However, the present invention is not limited to this.
An MD (Charge Modulation Device) may be used.

FIG. 18 is a block diagram showing a fifth embodiment of the present invention, in which an FPN is detected by accumulative addition in the third embodiment.

In this embodiment, the output of the accumulator 25 is stored as FPN, and the coefficient C
_The subtraction process is performed by multiplying _N.
Here, the number of examples 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.

[0092]

[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 blocked. Use of the dynamic shutter means 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 _Fclose , incident light amount is zero), it is needless to say that this can be used as a shutter.

Next, referring to FIG. 19, a sixth embodiment of the present invention will be described.
An example will be described. In this embodiment, a non-destructive readable solid-state imaging device is used to obtain a plurality of images having different exposure times within one exposure period.

The image processing circuit 29 shown in FIG. 19 is a D / A converter from the video processor circuit 7 shown in FIG.
It is assumed that the circuit is up to 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 described above. A slice circuit 42 is inserted between the subtractor 23 and the accumulator 25, and a linear conversion circuit 43 is inserted between the accumulator 25 and the image processing circuit 29.

Here, non-destructive reading by the CMD 18a will be described with reference to FIG. In the figure, a reset (RST in the figure) is executed at time "0", and the accumulation of electric charge is started. Then, the signal read-out (the READ) is performed when the elapsed time t _1. Then, the signal is read when t ₂ has elapsed. At this time,
The data to be read is the signal that was 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, if only reading is performed without executing reset, 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 amplified by the preamplifier 20 and subjected to processing such as clamping by the signal processing circuit 21,
Further, the data is converted into a digital signal by the A / D converter 22. The FPN is removed from the converted data in the subtractor 23. Then, the signal is clipped by the slice circuit 42 and the cumulative addition circuit
At 25, images with different exposure times are sequentially added. 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. The figure shows an example in which reading is performed five times during one exposure period.
₁ long exposure time is the most, the most exposure time is shorter same f _5, and a photoelectric conversion characteristic. Since the exposure time is short, the saturation luminance is high.

Now, it is assumed that the electrical conversion characteristic outputs of f _{1 to} f ₅ are sliced by the slice circuit 42 at V ₁ . The output of the f ₁ ~f ₅ is by being accumulated and added by the cumulative addition circuit 25, the photoelectric conversion characteristics shown in the figure F ₀ is obtained. If non-destructive reading 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 accumulated 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.
Then, after being converted to a linear signal, the image is monitored by the image processing circuit 29.
The signal is converted into a signal suitable for 37 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 luminance signal is converted by the video processor 7 of the image processing circuit 29 to perform matrix conversion. 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 generating circuit, which includes an adder 44a, a square detector 44b, an LPF 44c, and a square root circuit 44d. One of the outputs of the standard deviation generating circuit 44 is input to the other of the comparison amplifiers 45 connected to the variable resistor VR2, and is compared and amplified with the reference voltage. The output of the comparison amplifier 45 is supplied to the other input of the changeover switch 46, one of which is connected to the variable resistor VR4.
Is output as

The LPF 47 is for obtaining an average value of the luminance signal. The output of the LPF 47 is compared with a gain reference voltage by a comparison amplifier 48 connected to the variable resistor VR1. Then, by switching the gain setting voltage set by the variable resistor VR3 and the output of the comparison amplifier 48 with the 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, α and β signals can be obtained from Y (luminance signal). 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 DGC8c is described in JP-A-63-23.
No. 2591, etc., and are omitted here. Also,
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 operation, 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 in front of the A / D converter 22 is unstable, it may be clamped by the digital section after A / D conversion.

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 apparatus used in the present invention is disclosed in Japanese Patent Application Laid-Open No. Sho 63-232591, and Japanese Patent Application No. Hei.
34508, the details are omitted.

[0110]

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 in 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. 19;

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]

14 optical system, 15 half mirror, 16 aperture, 17 F-number control circuit, 18 CCD image sensor, 19 CCD drive circuit, 2
0, 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 ... brightness 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: Brightness Arithmetic unit, 335 ... counter

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Takeshi Mori 2-43-2 Hatagaya, Shibuya-ku, Tokyo Inside Olympus Optical Industry Co., Ltd. (56) References JP-A-63-246985 (JP, A) JP-A-63-246985 Hei 2-50584 (JP, A) JP-A-62-285584 (JP, A) JP-A-63-86976 (JP, A)

Claims (2)

(57) [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 A solid-state image sensor control means for controlling a time during which the subject is exposed on the solid-state image sensor; a cumulative addition number control means for controlling a cumulative number of image signals in the cumulative addition means; Storage means for storing the fixed pattern noise of the element; before converting the image signal into a format compatible with an external device, the image signal output from the accumulation means is stored in the storage means. Subtracting means for subtracting the fixed pattern noise from the object; 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 signal and a luminance lower limit signal; Based on the width of the dynamic range of the subject determined from the ratio between the upper limit signal and the lower luminance signal, optimal numerical 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 a control signal as a control signal to a corresponding light amount adjustment unit, a solid-state imaging device control unit, and a cumulative addition number control unit. 2. A solid-state imaging device for imaging a subject and converting the image signal into an electrical image signal; a unit for reading an image signal of the captured subject from the solid-state imaging device; An exposure control circuit for an image input apparatus, comprising: an accumulating means for accumulating image signals, wherein the solid-state imaging device is non-destructive at different times during a period in which the subject is exposed for imaging. A solid-state imaging device capable of reading the image signal at; and a light amount adjusting means for adjusting an incident light amount incident on the solid-state imaging device from the subject; and the subject for imaging during the exposure period. Solid-state imaging device control means for controlling the exposure time; cumulative addition number control means for controlling the cumulative addition number of the image signal in the cumulative addition means; and converting the cumulatively added data into a linear signal. You Conversion
Means and a subject brightness detecting means for outputting a signal for determining an upper limit value and the lower limit value of the brightness of the subject, of the subject output from the subject brightness detecting means luminance
The object generated from the signal defining the upper and lower limits of
Depending on the dynamic range width of the subject determined from the ratio between the upper limit value and the lower limit value of the body brightness or a condition corresponding to the dynamic range width, the incident light amount, the exposure time, and the cumulative addition number Optimum numerical values are set, and each numerical value is used as a control signal,
Exposure control circuit of the image input apparatus characterized by comprising a condition setting means for outputting to the solid-state imaging element control means and the accumulating number of control means.