JP2000134544A - Electronic camera - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic camera which prevents release time lag due to the increase of integration time and read time from increasing and a consecutive photographing speed from dropping and correctly executes the elimination of fixed pattern noise from image data. SOLUTION: The light receiving plane of an image sensor 11 outputting image data is made possible to shield the light by a focal plane shutter 10. Dummy image data due to prescribed exposure time is read at the state where the focal plane shutter 10 is operated and the light receiving plane of the sensor 11 is shielded. The dummy image data and the prescribed exposure time are stored as image quality correction data in a DRAM 29 by an image data controller 25. And, the controller 25 uses the stored image quality correction data and performs image correction of the latest photographed image data in accordance with prescribed conditions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic camera which captures a subject image by an image sensor, and more particularly to an electronic camera using a solid-state image sensor in which fixed pattern noise is eliminated.

[0002]

2. Description of the Related Art Conventionally, as described in, for example, Japanese Patent Application Laid-Open No. Hei 8-51571, an electronic image pickup apparatus includes an image pickup device and an exposure control shutter for controlling transmission of subject light to the image pickup device. Have. In this electronic imaging device,
After the image data is read from the image sensor in the light transmitting state of the shutter, the fixed pattern noise (Fixed Pa
In order to measure ttern noise (FPN),
Image data is read from the image pickup device in a light-shielded state of the shutter. Then, image data that does not include fixed pattern noise is generated from the two image data.

[0003]

Since the fixed pattern noise changes depending on the exposure time and temperature of the image pickup device, the data of the fixed pattern noise must be taken in order to completely remove the fixed pattern noise from the image data. It is desirable to measure each time.

However, in order to measure the fixed pattern noise for each photographing operation, the image pickup device is required to perform two charge accumulation operations in one photographing operation. Requires twice the integration time.

In recent years, the number of pixels of an image sensor has been increasing in order to improve the image quality of digital cameras. The increase in the number of pixels leads to an increase in the time required to read image data from the image sensor. Therefore, if the data of the fixed pattern noise is measured every time, the reading time is also doubled.

[0006] The increase in the integration time or the readout time results in an increase in the release time lag or a decrease in the continuous shooting speed in the operation sequence of the camera. SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and prevents an increase in release time lag due to an increase in integration time and readout time, and prevents a reduction in continuous shooting speed, and correctly removes fixed pattern noise from image data. It is an object to provide a possible electronic camera.

[0007]

That is, the present invention provides an image pickup device for outputting image data, a light shielding means capable of shielding a light receiving surface of the image pickup device, and a light receiving surface of the image pickup device by operating the light shielding means. Means for reading dummy image data with a predetermined exposure time in a state where light is shielded, and storing the dummy image data and the predetermined exposure time as image quality correction data; and A correction unit that corrects the image quality of the latest photographed image data using the correction data.

In the electronic camera according to the present invention, the light receiving surface of the image sensor for outputting image data can be shielded from light by the light shielding means. Then, in a state where the light shielding means is operated and the light receiving surface of the image sensor is shielded from light, dummy image data is read out for a predetermined exposure time. The dummy image data and the predetermined exposure time are stored as image quality correction data by the correction data sampling means. And
According to a predetermined condition, the image quality correction of the latest photographed image data is performed by the correction unit using the stored image quality correction data.

In the electronic camera according to the present invention, when correcting the fixed pattern noise, it is determined whether or not the fixed pattern noise (FPN) data already measured exists. Then, if FPN data exists, the measurement condition when the FPN data is measured is compared with the current imaging condition. As a result of the comparison, when it is determined that the FPN data is usable, the image data is corrected based on the usable FPN data. On the other hand, if it is determined that the data cannot be used, the FPN data is measured, and the image data is corrected based on the measured data. Then, this data and the photographing conditions (measurement conditions) at this time are stored so as to prepare for the next correction operation.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of the first embodiment of the present invention, and is a block diagram of an electronic imaging camera.

In FIG. 1, a photographic light beam from a subject image (not shown) can be rotated in the direction shown by an arrow in FIG. It is led to 3. The central part of the quick return mirror 3 is a half mirror,
When the quick return mirror 3 is down, a part of the light beam is transmitted. Then, the transmitted light flux is reflected by the sub mirror 4 installed on the quick return mirror 3 and
It is led to the F sensor 5.

On the other hand, the photographing light beam reflected by the quick return mirror 3 reaches the photographer's eyes via the pentaprism 6 and the eyepiece 7. When the quick return mirror 3 is raised, the light beam from the photographing lens 1 reaches an image sensor 11 typified by a CCD or the like as an image sensor via a filter 9 and a focal plane shutter 10 as a mechanical shutter. The filter 9 has two functions, one is a function of cutting infrared rays and guiding only visible light to the image sensor 11, and the other is a function as an optical low-pass filter. The focal plane shutter 10 has a front curtain and a rear curtain, and transmits a light flux from the photographing lens 1.
This is a light shielding means for controlling the interruption.

When the quick return mirror 3 is raised, the sub mirror 4 is folded. The system controller 15 includes a CPU, and includes a control unit that controls the entire electronic imaging camera, first and second reading units, and a determination unit. The system controller 15 includes a lens drive mechanism 16 for moving the photographing lens 1 in the optical axis direction for focusing, an aperture drive mechanism 17 for driving the aperture 2, and a quick return mirror 3. A mirror driving mechanism 18 for performing up / down driving, a shutter charging mechanism 19, a shutter control circuit 20 for controlling traveling of a front curtain and a rear curtain of the focal plane shutter 10, and an image sensor 11.
, A photometric sensor 22 installed near the eyepiece 7, and an EEP in which parameters that need to be adjusted to control the system are stored.
The ROM 23 is connected.

The photometric sensor 22 is a sensor for measuring the brightness of a subject (not shown), and its output is supplied to the system controller 15. The temperature sensor 21 is a temperature measuring means for detecting the temperature of the image sensor 11. The output of the temperature sensor 21 is required when correcting fixed pattern noise generated by the image sensor 11. A typical example of the temperature sensor is a thermistor whose resistance changes according to the temperature. Ideally,
It is preferable that a temperature sensor be present on a CCD chip serving as an image sensor. Since the forward voltage generated at the PN junction changes according to the temperature, this voltage change may be detected.

The system controller 15 can form a subject image on the image sensor 11 by controlling the lens driving mechanism 16. Further, the system controller 15 controls the aperture driving mechanism 17 for driving the aperture 2 based on the set Av value, and further outputs a control signal to the shutter control circuit 20 based on the set Tv value. I do.

The front curtain and the rear curtain of the focal plane shutter 9 have a drive source constituted by a spring, and after the shutter travels, a spring charge is required for the next operation. The shutter charging mechanism 19 is provided for the spring charging.

An image data controller 25 is connected to the system controller 15. The image data controller 25 is a correction data sampling unit and a correction unit configured by a DSP (Digital Signal Processor), and controls the image sensor 11 and corrects and processes image data input from the image sensor 11. It is executed based on a command from the controller 15.

The image data controller 25 includes a timing pulse generating circuit 27 for outputting a pulse signal necessary for driving the image sensor 11, and a timing pulse generated by the timing pulse generating circuit 27 together with the image sensor 11. Receiving, image sensor 1
An A / D converter 28 for converting an analog signal corresponding to the subject image output from 1 into a digital signal;
A DRAM 29 for temporarily storing the obtained image data (digital data), a D / A converter 30 and an image compression circuit 33 are connected.

The DRAM 29 is used as storage means for temporarily storing image data before processing or data conversion into a predetermined format. Also,
An image display circuit 32 is connected to the D / A converter 30 via an encoder 31. Further, an image data recording medium 34 is connected to the image compression circuit 33.

The image display circuit 32 is a circuit for displaying image data picked up by the image sensor 11, and is generally constituted by a color liquid crystal display element.
The image data controller 25 converts the image data on the DRAM 29 into an analog signal by the D / A converter 30 and outputs the analog signal to the encoder circuit 31. Then, in the encoder circuit 31, the output of the D / A converter 30 is converted into a video signal (for example, an NTSC signal) necessary for driving the image display circuit 32.

The image compression circuit 34 compresses or converts image data stored in the DRAM 29 (for example, JPEG).
Is a circuit for performing the following. The converted image data is stored in the image data recording medium 34. As this recording medium, a hard disk, a flash memory, a floppy disk, or the like is used.

Further, the system controller 15 includes an operation display circuit 36 for displaying information on the operation mode of the camera and exposure information (shutter time, aperture value, etc.), and an electronic image pickup operation desired by the user. An operation switch (SW) 37 composed of a number of switches operated by the camera is connected.

The operation switches 37 include a release switch, a power switch, and an image display selection switch. The function of each switch will be described later. Next, FIG.
The operation of the main routine of the system controller 15 will be described with reference to the flowchart of FIG.

When a power switch, which is one of the operation switches 37, is turned on and power is supplied to the camera system, the operation of the system controller 15 is started.
Then, first, the system is initialized in step S1. This is the initialization of the I / O port of the system controller 15, the initialization of the memory, and the like. Also, an instruction for an initialization operation is issued to the image data controller 25.

Next, in step S2, the fixed pattern noise (FPN) input flag which is a control flag is cleared (← “0”). The FPN input flag is set when the measurement of the FPN data is performed and this data exists in the DRAM 29. Immediately after starting the camera system, this data does not exist, so the flag must be cleared. In step S3, the image quality counter is cleared (← “0”). Table 1 below shows the relationship between the value of the image quality counter and the compression ratio of the image data.

[0026]

[Table 1]

The image data input from the image sensor 11 needs to be compressed when stored in the image data recording medium 34 to reduce the data capacity. The image counter indicates the compression ratio at the time of this compression operation. Since the initial value of the compression ratio is １ ／, the image quality counter is cleared in step S3.

Next, in step S4, the photometric sensor 2
2, the luminance data of the subject is input. Then, in step S5, the aperture setting value and the shutter time (Ts) are calculated based on the luminance data and the sensitivity of the image sensor 11. In step S6, data indicating the operation state of the camera is output to the operation display circuit 36. This step S
Since the operation of No. 6 is periodically executed in the main routine, the display section of the operation display circuit 36 always displays the new operation state of the camera.

In step S7, the state of the image quality selection switch, one of the operation switches 37, is detected. Here, when the operation of the image quality selection switch is detected, the process proceeds to step S8, and when not detected, the process proceeds to step S11.

In step S8, the image quality counter is incremented (+1). Next, in step S9,
It is determined whether or not the image quality counter is "3". Here, if the value of the image quality counter is not "3", the process proceeds to step S4. On the other hand, if the image quality counter is "3", the process proceeds to step S10, where the counter value is cleared (← "0"), and then proceeds to step S4.

The processing in steps S9 and S10 is necessary because, as shown in Table 1, the compression ratio of image data is defined for the image quality counter "0 to 2".

In step S11, the state of the release switch, one of the operation switches 37, is detected. Here, when the operation of the release switch is detected, the process proceeds to step S14, and when not detected, the process proceeds to step S12.

In step S12, the operation switch 3
7, the state of the power switch is detected. Here, if the power switch is on, the system is operable, and the process proceeds to step S14. On the other hand, if the power switch is off, the process proceeds to step S13, and after the processing for system down is executed, the operation of the system controller 15 is stopped.

In step S14, a focus adjustment operation is performed. That is, information on the amount of focus shift is input from the AF sensor 5, and the lens driving mechanism is controlled based on this information. Then, in step S15, the aperture drive mechanism 17 is controlled based on the calculated aperture value.

Next, in step S16, the mirror drive mechanism 18 is controlled to drive the quick return mirror 3 to the up state. In step S17, a front curtain start signal of the focal plane shutter 10 is output to the shutter control circuit 20. Then, in step S18, the process stands by until the traveling of the front curtain of the shutter is completed.

Next, in step S19, the counting operation of the timer counter for counting the seconds of the focal plane shutter 10 is started. Then, in step S20, an instruction is issued to the image data controller 25 to start the integration operation of the image sensor 11.

In step S21, the process waits until the value of the timer counter reaches the calculated shutter time (Ts). Here, when the value of the timer counter reaches Ts, the flow shifts to step S22, where the focal plane shutter 1
0 is output to the shutter control circuit 20.

In step S23, the system waits for the trailing curtain to finish running. Next, in step S24,
Image sensor 1 for image data controller 25
The end of the integration of 1 is instructed, and further, the image sensor 11 instructs to take in the image data in step S25. Thus, by the image data controller 25,
Image data is taken in from the image sensor 11, and D
It is temporarily stored in the RAM 29.

In step S26, the mirror driving mechanism 18
Is controlled, and the quick return mirror 3 is moved to the down state. Next, in step S27, the aperture driving mechanism 17 is controlled to drive the aperture 2 to the open position.

Then, in step S28, the shutter charging mechanism 19 is controlled to perform a charging operation of a spring for driving the front curtain and the rear curtain of the focal plane shutter 10. In step S29, the subroutine "FPN"
In this subroutine, the fixed pattern noise is removed from the image data. When this subroutine is completed, the process proceeds to step S4 for the next photographing operation.

Next, referring to the flowchart of FIG.
The operation of the subroutine "FPN correction" of step S29 in the flowchart of FIG. 3 will be described. In step S31, the temperature sensor 21 transmits the image
Temperature data is input. Next, in step S32, two parameters (allowable temperature Δtmp and allowable second time coefficient Tk) necessary for determining whether or not the FPN data measurement operation is performed are read from the EEPROM 23.

The fixed pattern noise has a temperature of 8 ° C. to 10 ° C.
When the temperature rises by about ℃, it increases about twice. It increases almost in proportion to the integration time. In order to reliably remove FPN from image data, FPN must be performed under the same conditions as imaging conditions (temperature, integration time).
It is desirable that the image data is corrected based on the FPN data obtained by this measurement operation. However, depending on the image quality of the image data required,
Even FPN data measured under conditions different from the shooting conditions can be used for the correction operation.

The allowable temperature (Δtmp) indicates an allowable temperature difference between the temperature at the time of photographing and the temperature at the time of FPN measurement. The permissible second time coefficient (Tk) is a coefficient necessary for calculating a permissible difference between the integration time at the time of photographing (shutter time) and the integration time at the time of FPN measurement. These two parameters need to be determined in consideration of the characteristics of the image sensor 11 and the desired image quality, and it is difficult to determine them uniformly. Therefore, the data is stored in the EEPROM 23. Therefore, the parameter can be changed as needed, which is convenient.

The image data read from the image sensor 11 has a large data capacity as it is and is difficult to handle. Therefore, the data is generally compressed to reduce the capacity. In the electronic imaging camera according to this embodiment, the compression ratio of image data can be changed.

Image data deteriorates in image quality as the compression ratio increases. If the image quality deteriorates, the influence of the FPN becomes smaller. In this case, there is no problem even if the correction operation is performed using FPN data measured under conditions slightly different from the photographing conditions. Then, the values of Δtmp and Tk are
It is more convenient if it can be changed according to the compression ratio of the image data. Therefore, as shown in Table 2 below,
Δtmp and Tk are stored in the EEPROM 23 in correspondence with the respective values of the image quality counter.

[0046]

[Table 2]

In step S33, the temperature (TMPlast) and the integration time (Tslast) of the image sensor 11 when the fixed pattern noise is measured are read from the EEPROM 23. Next, in step S34, FPN
The state of the flag is determined.

Here, if the FPN flag is "0",
This indicates that the measurement of the FPN data has never been performed. Therefore, the process moves to step S41 for the operation of measuring the FPN data. On the other hand, if the FPN flag is “1”, it indicates that the FPN data exists on the DRAM 29. Therefore, in this case, the process proceeds to step S35.

In step S41, the image data controller 25 is instructed to start integration of the image sensor 11. Next, in step S42, the counting operation of the timer counter for measuring the integration time (the shutter time) is started. Further, in step S43, the process waits until the value of the timer counter reaches Ts (the shutter time calculated in step S5 in the flowchart of FIG. 2).

In step S44, the image data controller 25 is instructed to terminate the integration. Further, in step S45, an instruction is given to take in image data from the image sensor 11. The data captured here is data captured in a state where the focal plane shutter 10 is shielded from light, and is FPN data. The FPN data is stored on the DRAM 29.

In step S46, the FPN input flag is set (← “1”). Next, in step S47, the current temperature (TMPx) of the image sensor 11 is set to T
It is stored in the EEPROM 23 as MPlast.

In step S48, the shutter time (T
s) is stored in the EEPROM 23 as Tslast.
Then, the process proceeds to step S38 in order to correct the image data based on the measured FPN data.

On the other hand, in step S35, the temperature (TMPlast) of the image sensor 11 at the time of measuring the FPN data is determined.
Is compared with the current temperature (TMPx) of the image sensor 11, and a difference between these temperatures is determined as an allowable temperature (Δtmp).
It is determined whether it is smaller than. Here, if it is smaller than Δtmp, the process proceeds to step S36, but if it is larger than Δtmp, it is necessary to measure the FPN data, so that the process proceeds to step S41.

In step S36, a comparison is made between the integration time (Tslast) of the image sensor 11 when measuring the FPN data and the shutter time (Ts) during the photographing operation. That is, first, the determination value is calculated from the current shutter time. For example, assuming that Ts is 1/60 (second) and the image quality counter is “2”, Tk is 2.0. Therefore, the judgment value is (1/60) × (1/2) ² (= 1/25)
0) and (1/60) × 2 ² (= 1/15).

Therefore, in step S36, T
If slast is a value between 1/250 and 1/15, the process proceeds to step S37. On the other hand, if Tslast is not in this interval, it is necessary to measure FPN data, and thus the flow shifts to step S41.

In step S37, the image data controller 25 is instructed to perform an FPN data conversion operation. FPN already measured and stored in DRAM 29
The data is data measured during the integration time (Tslast). Therefore, the value of F adjusted to the shutter time (Ts)
Must be converted to PN data.

The size of the FPN data changes in proportion to the integration time. The FPN data shows that the temperature is 8 ° C.
When it changes by 〜１０10 ° C., it changes about twice. In consideration of the temperature of the image sensor 11 at the time of measuring the FPN data and the current temperature of the image sensor 11, it is necessary to convert the FPN data already existing in the DRAM 29. Therefore, the conversion equation is as the following equation (1).

[0058]

(Equation 1)

In step S37, the Ts, Tslast, TMPlast,
TMPx and Δt are output, and execution of the above equation (1) is instructed.

Subsequently, in step S38, the image data controller 25 is instructed to remove the FPN data from the image data. And step S
At 39, the image data controller 25 is instructed to compress the image data. Here, the compression ratio is a value determined by the value of the image quality counter.

Finally, in step S 40, the image data controller 25 is instructed to transfer the compressed image data to the image data recording medium 34. Then, the process returns to the main routine.

According to the above embodiment of the present invention,
The following configuration can be obtained. (1) an image sensor for outputting image data, a shutter capable of blocking a light receiving surface of the image sensor, first reading means for reading image data of the image sensor in a state where the shutter is not shielded under predetermined shooting conditions, Second reading means for reading out image data of the image sensor with the shutter being shielded from light under predetermined measurement conditions; storage means for storing the image data read by the second reading means and the measurement conditions; (1) After the operation of the reading means is completed, the photographing conditions are compared with the measurement conditions stored in the storage means, and based on the image data stored in the storage means, correction is performed on the read image data of the first reading means. An electronic camera, comprising: a determination unit configured to determine whether or not the electronic camera is not in use.

(2) The electronic camera according to (1), wherein the determination means makes a determination in consideration of the integration time of the image sensor when comparing the photographing condition and the measurement condition.

(3) The electronic camera according to (1), wherein the determining means makes a determination in consideration of the temperature data of the image sensor when comparing the photographing condition and the measurement condition.

[0065]

As described above, according to the present invention, an increase in the release time lag due to an increase in the integration time and the readout time and a decrease in the continuous photographing speed are prevented, and the fixed pattern noise is correctly removed from the image data. A possible electronic camera can be provided.

[Brief description of the drawings]

FIG. 1 shows a configuration of a first exemplary embodiment of the present invention, and is a block configuration diagram of an electronic imaging camera.

FIG. 2 is a flowchart illustrating an operation of a main routine of a system controller 15 of FIG. 1;

FIG. 3 is a flowchart illustrating an operation of a main routine of a system controller 15 of FIG. 1;

FIG. 4 is a step S29 in the flowchart of FIG. 3;
4 is a flowchart for explaining the operation of a subroutine "FPN correction" of FIG.

[Explanation of symbols]

 Reference Signs List 1 shooting lens, 2 aperture, 3 quick return mirror, 5 AF sensor, 7 eyepiece, 9 filter, 10 focal plane shutter, 11 image sensor, 15 system controller (CPU), 16 lens drive mechanism, 17 aperture drive mechanism, 18 Mirror drive mechanism, 19 shutter charge mechanism, 20 shutter control circuit, 21 temperature sensor, 22 photometric sensor, 23 EEPROM, 25 image data controller (DSP), 29 DRAM, 32 image display circuit, 33 image compression circuit, 34 image data recording Media, 36 operation display circuit, 37 operation switch (SW).

Claims (2)

[Claims] An image sensor for outputting image data; a light-shielding means capable of shielding a light-receiving surface of the image-acquisition element; Correction data sampling means for reading the dummy image data and storing the dummy image data and the predetermined exposure time as image quality correction data; and, according to a predetermined condition, a latest photographed image using the stored image quality correction data. An electronic camera, comprising: a correction unit that corrects image quality of data. 2. The method according to claim 1, wherein the predetermined condition is that the latest exposure time of the image sensor is compared with the stored predetermined exposure time, and that a difference between the two is within a predetermined range. The electronic camera according to claim 1, wherein: