JP2006352434A - Imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging device capable of securely performing proper luminance adjustment and proper color tone adjustment when a picture is taken in whatever temperature environment. <P>SOLUTION: A black level is read out of an area where no photodetection sensor is present. A temperature nearby a CCD is detected by a temperature sensor. A correction signal is generated by referring to a correction table previously stored in an EEPROM and set in an image signal processing circuit and an AE detecting circuit. Both the image signal processing circuit and the AE detecting circuit are made to accurately calculate signal quantities of a Y signal in the image signal generated by the CCD. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an imaging apparatus that generates an image signal by forming a subject image on an imaging element in which a large number of light receiving sensors are two-dimensionally arranged.

  In a digital camera, when processing an image signal output from an image sensor, a partial area including some of the many light receiving elements constituting the image sensor is shielded, and an output signal from the light shield area In many cases, a black level is used to perform image signal processing in a subsequent image signal processing unit. Thus, when the black level is correctly determined as the pedestal level, the image signal output from the image sensor is clamped to the pedestal level, and the luminance level is correctly detected. As is well known, a digital camera or the like is provided with a white balance circuit, and the white level is also detected by the white balance circuit. Therefore, the operation range from the black level to the white level, that is, the dynamic range is set to the pedestal level. Therefore, it is ensured correctly, and halftone color adjustment in the signal processing unit can be performed with high accuracy.

  By the way, although the semiconductor manufacturing technology has been improved and the yield rate of an image pickup device in which a large number of light receiving sensors are two-dimensionally arranged has been improved, some of the many light receiving sensors that still form the pixels of the image pickup device still remain. A defect may occur and a defective pixel may be formed in some pixels constituting one image sensor. When such a defective pixel is formed, a signal indicating a white level may be output without outputting a signal indicating a black level despite being shielded from light. If such defective pixels are formed in the light-shielding region, the pedestal level cannot be determined correctly, and a dynamic range from the black level to the white level cannot be secured sufficiently, so that the halftone color tone cannot be adjusted well.

  In view of this, there is also an image sensor in which the black level is stabilized by not forming a pixel in the light shielding region in order to suppress the influence of defective pixels. As described above, when the light receiving sensor is not formed in the light shielding region, the black level is stabilized.

  However, in the case of a conventional imaging device, a light shielding region is formed by applying a light shielding film to the light receiving sensor, so that the temperature characteristics of the light receiving sensor are also reflected in the pedestal level determined by the black level. However, if an image sensor that does not include a light receiving sensor as described above is used, a situation occurs in which the temperature characteristics of the light receiving sensor are not reflected on the pedestal level. In other words, when shooting with an imaging device having an image sensor having a non-existing light-shielding area, the black level that should change due to a change in the temperature of the image sensor does not change. Accordingly, there is a possibility that appropriate brightness adjustment and proper color tone adjustment cannot be performed.

Here, as a technique for correcting the black level according to a change in temperature or the like, there is a technique for creating a black level reference signal using an image signal for one frame (see, for example, Patent Document 1). The first technique is a technique for improving the response of the aperture control loop of the diaphragm to perform accurate diaphragm control. For the above-described luminance adjustment and color tone adjustment in the image signal processing unit. It's not about getting a black level to become a pedestal level.
Japanese Patent Publication No. 7-22355

  SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide an imaging apparatus capable of accurately performing appropriate luminance adjustment and appropriate color tone adjustment regardless of the temperature environment.

A first imaging device of the present invention that achieves the above object is an imaging device that generates an image signal by forming a subject image on an imaging device in which a large number of light receiving sensors are two-dimensionally arranged.
The imaging element is a region where there is no light receiving sensor and has a black level detection region that can be read from the region,
A black level detection unit that reads the black level detection region and generates a correction signal representing the black level;
An image signal processing unit that corrects a signal read from the light receiving sensor on the image sensor with a correction signal generated by the black level detection unit;
It has a temperature detector that detects the temperature,
The black level detection unit generates a correction signal corresponding to the temperature detected by the temperature detection unit.

  According to the first imaging device of the present invention, when the black level detection unit reads out the black level detection area without the light receiving sensor and generates a correction signal representing the black level, the temperature detection unit A correction signal corresponding to the detected temperature is generated.

  As a result, the black level detection area in the absence of the light receiving sensor is read and the correction signal indicating the black level is fixedly generated. Will be performed. When the black level is accurately corrected to an appropriate value in accordance with the temperature in this way, luminance adjustment and color tone adjustment considering temperature can be performed when performing signal processing in the signal processing unit.

  That is, it is possible to realize an imaging apparatus that can perform appropriate brightness adjustment and appropriate color tone adjustment with high accuracy regardless of the temperature environment.

Here, it has a sensitivity setting section to set the shooting sensitivity,
The black level detection unit preferably generates a correction signal corresponding to the temperature detected by the upper temperature detection unit and the sensitivity set by the sensitivity setting unit.

  For example, if a lookup table is prepared as a component of the black level detection unit and the correction signal is generated by referring to the lookup table in accordance with the temperature and the sensitivity, not only the temperature but also the temperature is generated. Correction according to sensitivity can be easily performed.

A second imaging device of the present invention that achieves the above object is an imaging device that generates an image signal by forming a subject image on an imaging device in which a large number of light receiving sensors are two-dimensionally arranged.
The imaging element is a region where there is no light receiving sensor and has a black level detection region that can be read from the region,
A black level detection unit that reads the black level detection region and generates a correction signal representing the black level;
An image signal correction unit that corrects a signal read from the light receiving sensor on the image sensor with a black level signal generated by the black level detection unit;
With a time measurement unit that measures the elapsed time after power on,
The black level detection unit generates a correction signal corresponding to the time measured by the time measurement unit.

  Since the use of the temperature detection unit as in the first imaging apparatus of the present invention leads to an increase in cost, the time measurement unit may be used instead of the temperature detection unit as in the second imaging apparatus. . Even if it does in this way, the effect similar to the said 1st imaging device is acquired.

As with the first photographing apparatus, a sensitivity setting unit for setting photographing sensitivity is provided.
More preferably, the black level detection unit generates a correction signal corresponding to the time set by the time setting unit and the sensitivity set by the sensitivity setting unit.

   As described above, it is possible to realize an imaging apparatus that can perform appropriate luminance adjustment and, consequently, appropriate color tone adjustment, regardless of the environment in which shooting is performed.

  Hereinafter, the configuration of an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is an external perspective view of a digital camera 10 that is an embodiment of a photographing apparatus of the present invention as viewed obliquely from above. FIG. 1A shows a view of the front of the digital camera 10 as viewed from diagonally above, and FIG. 1B shows a view of the back of the digital camera 10 as viewed from diagonally above. Yes.

  In the center of the front surface of the digital camera 10 shown in FIG. 1A, a zoom lens barrel 10_1 having a photographing lens 10_1a, which is an optical zoom lens, is provided. Above the zoom lens barrel 10_1, there is provided a flash light emission window 10_2 for irradiating flash light toward the subject when the field luminance is low. Further, an optical viewfinder objective window 10_3 that is paired with an optical viewfinder eyepiece window (described later) on the back side is provided next to the flash light emission window 10_2. A release button 10_4 is provided on the top surface of the digital camera 10.

  On the other hand, an optical viewfinder eyepiece window 10_5, a viewfinder lamp 10_6 that lights up when shooting preparation is completed or flashes during shooting, and a shooting mode and a playback are displayed on the upper back of the digital camera 10 shown in FIG. There are provided a mode switch 10_7 for switching modes, a zoom button 10_8 for zooming up to the wide-angle side (wide side) when pressed and zooming up to the telephoto side (tele side) when pressed.

  Below the zoom button 10_8, a menu / OK button 10_9, a DISP button 10_10, and a BACK button 10_11 are provided. The menu / OK button 10_9 is a button for displaying various menus at the time of shooting and reproduction and determining a selected menu. The DISP button 10_10 is a button for switching the state of the screen displayed on the LCD monitor 10_301 beside the button. For example, the display of the LCD monitor 10_301 is turned on / off during photographing, and the character display is turned on during reproduction. Or turn it off. The BACK button 10_11 is a button for returning or canceling the operation state by the MENU / OK button 10_9 or the like. The POWER button 10_12 below the button is a button for turning on the power.

  FIG. 2 is a block diagram showing a circuit configuration of the digital camera 10 shown in FIG.

  FIG. 2 also shows a photographic lens necessary for operating the circuit after the image sensor 10_41. In order to show what the photographic lens is, a zoom which is a main component of the photographic lens is shown. A lens 10_1a1 and a focus lens 10_1a2 are illustrated. The photographing lens 10_1a including these lenses causes subject light to form an image on the subsequent CCD 10_41, and the CCD 10_41 generates an image signal representing the subject light.

The digital camera 10 is centrally controlled by a CPU 10_47, and the CPU 10_47 in this example includes a program memory 10_470.
Hereinafter, it will be described how the CCD 10_41 generates an image signal and how the generated image signal is transmitted to a subsequent circuit.

  First, the flow of an image signal representing a through image displayed on the LCD monitor 10_301 when the power switch 10_12 is turned on and the mode switch 10_7 is in the shooting mode side will be described.

  In order to cause the CCD 10_41 to generate an image signal for a through image, the CCD 10_41 is caused to repeatedly supply an exposure start signal and an exposure end signal to the CCD 10_41 at a predetermined cycle by a timing generator (not shown) under the control of the CPU 10_47 described later. Generation of an image signal representing a through image is performed every predetermined period. In response to the exposure end signal from the timing generator (not shown), after the exposure at the CCD 10_41 is ended, an image signal (hereinafter referred to as RGB signal) representing a through image that has been exposed almost simultaneously is output from the CCD 10_41. ing. On the light receiving surface of the CCD 10_41, there are two-dimensionally arranged light receiving sensors for receiving subject light, and there is also a black level detecting region in the absence of the light receiving sensor provided for detecting the black level. In this embodiment, the CPU 10_47 instructs the timing generator (not shown) and the image input controller 10_43 to read out a black level signal from the black level detection area, that is, the area without pixels, thereby detecting and correcting the black level. I try to do it. Details will be described later.

  When the RGB signal for the through image is output to the A / D conversion circuit 10_42 in this way, the analog RGB signal is converted into a digital RGB signal by the A / D conversion circuit 10_42. Then, the digital RGB signal is guided to the bus line 10_100 by the image input controller 10_43 in the subsequent stage.

  The digital RGB signal for the through image guided to the bus line 10_100 by the image input controller 10_43 is supplied to the image signal processing circuit 10_44, and the image signal processing circuit 10_44 converts the digital RGB signal to the digital YC signal. Is done. The YC signal converted by the image signal processing circuit 10_44 is supplied to the VideoEncoder 10_300, and an image based on the YC signal is displayed on the monitor 10_301 of the LCD which is an image display device. Since this YC signal is generated by the CCD 10_41 every predetermined cycle, an image based on the YC signal is switched and displayed on the LCD monitor 10_301 every predetermined cycle. In this way, the subject in the direction in which the photographing lens 10_1a is directed is displayed on the LCD monitor 10_301 as it is as a through image.

  That is, even if the LCD monitor 10_301 is viewed as a viewfinder instead of looking through the optical viewfinder, shooting is performed by pressing the release button 10_4 at a photo opportunity.

  Further, since the brightness adjustment and the focus adjustment are always necessary when displaying the through image in this way, the Y signal among the YC signals obtained by the image signal processing circuit 10_44 in the digital camera 1 of the present embodiment. Is also supplied to the AE detection circuit 10_50 and the AF detection circuit (not shown). Since these detection circuits detect the brightness or the in-focus position based on the image data (through image data) representing the subject in the direction to which the photographing lens is directed, the CPU 10_47 detects the AE detection circuit 10_50. In response to the detection result from, the driver (not shown) is instructed to adjust the aperture diameter of the aperture to perform exposure control, or the detection result from the AF detection circuit is instructed to the driver 10_60 to instruct the focus lens 10_1a2. It is driven to adjust the focus.

  In the present embodiment, in order to solve the above-described problem, the CPU 10_47 instructs the image input controller 10_43 to read the black level read from the black level detection area in the absence of the CCD light receiving sensor, and the temperature sensor 10_410. A correction signal representing the black level is generated using both the signal read from the correction table in the EEPROM 10_51 in accordance with the detected temperature. In this way, a reference signal representing the black level according to the temperature is generated by the CPU 10_47, and is set so that the reference signal becomes the pedestal level in both the AE detection circuit 10_50 and the image signal processing circuit 10_44. Thus, signal processing and exposure control according to temperature can be performed accurately.

  Thus, when exposure adjustment (such as adjusting the aperture diameter of the aperture) is accurately performed based on the detection result of the AE detection circuit 10_50 and the color tone adjustment is accurately performed by the image signal processing circuit 10_44, a clear through A through image based on the image signal is displayed on the LCD monitor 150.

  Here, when the release button 10_4 is pressed at a photo opportunity while seeing the through image on the LCD monitor, the photographing process is started. The release button 10_4 of this embodiment has two operation modes of half-press and full-press, and when the release button 10_4 is in the half-pressed state, one switch 10_4A is connected and the CPU 10_47 detects the half-pressed state. When fully depressed, the CPU 10_47 detects that the other switch 10_4B is also connected and fully depressed.

  The CPU 10_47 causes the AE detection circuit 10_50 and the AF detection circuit 10_51 to perform predetermined processing when half-pressing is detected, and causes the timing generator (not shown) to perform exposure corresponding to the shutter speed when full-pressing is detected. A start signal and an exposure end signal are output to the CCD 10_41.

  The AE detection circuit 10_50 detects the luminance necessary for exposure setting, and the CPU 1_47 adjusts the aperture diameter of a diaphragm (not shown) according to the detection result of the AE detection circuit 10_50 or is not shown when fully pressed. The flash light emitting device emits flash light. Similarly to the processing for the through image signal described above, the CPU 10_47 reads the value of the signal representing the black level read from the black level detection area in the absence of the light receiving sensor prior to photographing, and further detected by the temperature sensor 10_410. A value indicating the correction amount is obtained by referring to the temperature correction table in the EERPOM 10_51 according to the temperature, and the value obtained by subtracting the value indicating the correction amount from the black level value is used as the pedestal level, and the image signal processing circuit 10_44 and the AE process. It is set in the circuit 10_50. In this way, an appropriate pedestal level is set in the AE detection circuit 10_50 and the image signal processing circuit 10_44, and exposure such as an aperture and a shutter speed is performed according to the field luminance distribution detected by the AE detection circuit 10_50. Control is performed accurately, and appropriate color tone adjustment is performed in the image signal processing circuit 10_44.

  In addition, the AF detection circuit 10_50 (not shown) is controlled by the CPU 10_47, and the motor driver 10_60 is instructed to move the focus lens 10_1a2 from the closest point to the farthest point at each of a plurality of positions on the way. Subject contrast is detected, and processing is performed such that the peak of the subject contrast detected at each position is the focal point.

  In this way, after the image signal representing the image formed on the CCD 10_41 when fully pressed is output to the CCD 10_41, the RGB signals converted into digital signals by the A / D conversion circuit 10_42 are bus lines by the image input controller 10_43. 10_100.

  All the RGB signals guided to the bus line 10_100 are temporarily stored in the memory (SDRAM) 10_52, and then read out from the memory 10_52 and supplied to the image signal processing circuit 10_44. After the RGB signal is converted into the YC signal by the image signal processing circuit 10_44 and the color tone adjustment is performed, the adjusted YC signal is supplied to the compression processing circuit 10_45 and JPEG compressed by the compression processing circuit 10_45. . Further, the JPEG compressed YC signal is supplied to the medium controller 10_53, and an image file (Exif file) in which header information such as compression information is added to the YC signal is recorded on the recording medium 10_54 by the medium controller 10_53.

  FIG. 3 is a diagram for explaining the difference in black level between the black level detection area in the absence of the light receiving sensor and the pixel effective area in the presence of the light receiving sensor of the CCD 10_41.

  It can be seen from FIG. 3 that in the pixel effective area where the light receiving sensor is present (including pixels) including the effective pixel area, the temperature level of the light receiving sensor is reflected and the black level increases as the temperature increases. This means that if signal processing is not performed in consideration of the fact that the black level is offset according to the temperature, the signal accuracy of the corner black level (although the black reference level is made almost noiseless) is increased. This suggests that the signal amount at the time of signal processing changes between when the temperature is low and when the temperature is high. In other words, if the black level in the black level detection region in the absence of the light receiving sensor (no pixel) shown in FIG. 3 is used as it is for signal processing, proper signal processing is performed without considering the temperature characteristics of the light receiving sensor. It is to disappear.

  Therefore, the present applicant tries to solve the problems listed as problems by detecting the temperature of the CCD 10_41 itself with the temperature sensor 10_410 and offsetting the black level with the above signal accuracy enhanced (level shift) according to the temperature. Yes. Here, a black level correction value according to the temperature of the CCD 10_41 is experimentally acquired in advance, and the correction value is stored in the EEPROM 10_51. The correction according to the temperature detected by the temperature sensor 10_410 during the photographing process is performed. The correction signal is generated by reading the value from the table stored in the EEPROM 10_51 and offset the black level read from the area where the light receiving sensor is not present by the read value.

  Table 1 below shows an example of the correction table in EERPOM10_51.

  Table 1 shows a 12-bit correction value used when subtracting from the Y signal. For example, in the case of -3, the value indicated by 100000000011 is set in the AE detection circuit 10_50 and the image signal processing circuit 10_44 with the MSB as a sine (sgn) bit. Then, the black level offset according to the temperature is obtained by subtracting the value from the 12-bit signal indicating the light receiving level detected by each light receiving sensor of the CCD. When this offset level is set in the image signal processing circuit 10_44 or the AE processing circuit 10_50 and subtraction is performed with the actual signal, the signal amount (luminance Y signal) of each pixel is correctly calculated. . Since the sensitivity of this digital camera can be set by operating the menu / OK button 10_9 on the back side, a correction value corresponding to the sensitivity is also shown.

  FIG. 4 is a flowchart showing a procedure of processing performed by the CPU 10_47.

  In step S401, the black level in the absence region is calculated by reading from the absence region of the light receiving sensor. In step S402, the temperature near the CCD is detected by the temperature sensor 10_410, and the black level value calculated in step S403 is corrected using the table shown in Table 1 in consideration of the temperature characteristics (and sensitivity) of the light receiving sensor. Convert to signal. After the converted correction signal is set in the AE processing circuit 10_50 and the image signal processing circuit 10_44, the AE detection circuit 10_50 and the image signal processing circuit 10_44 are caused to calculate actual signal amounts, and the processing of this flow is finished.

  As described above, it is possible to realize an imaging apparatus capable of reliably performing appropriate luminance adjustment and appropriate color tone adjustment regardless of the temperature environment.

  Although the configuration of the first embodiment may be used, the temperature sensor 10_410 used in the first embodiment is expensive and increases the cost.

  As described above, the CCD 10_41 is a semiconductor element having temperature characteristics, and the temperature characteristics are different for each manufactured CCD. Therefore, the electrical characteristics corresponding to the temperature are individually obtained by experiment by, for example, placing the CCD in a temperature chamber. Temperature compensation tables must be created individually. If temperature data is to be acquired by experiment anyway, the temperature sensor is removed by associating the temperature with the passage of time, and the elapsed time is set by a timer (such as an external timer) built in the CPU 10_47 or the like. It is better to measure and read out the correction value according to the measurement time. Then, even if the timer is externally attached, the cost is far lower than using the temperature sensor.

  Therefore, in the second embodiment, how much the temperature rises according to the operating time of the CCD, that is, the elapsed time after power-on, is acquired in advance as experimental data, and the elapsed time and the correction value are obtained. The associated correction table is changed to be stored in the EEPROM 10_51. In the second embodiment, a timer circuit is added in place of the temperature sensor to refer to the correction table.

  FIG. 5 is a diagram showing an internal configuration of an example including the timer circuit. FIG. 6 is a flowchart showing the procedure of the photographing process performed by the CPU 10_47.

  FIG. 5 has the same configuration as FIG. 2 except that the temperature sensor 10_410 is removed and a timer circuit 10_471 is added. Further, the contents of the correction table in the EEPROM 10_50 are changed to Table 2 below.

  As shown in Table 2, the configuration is exactly the same as in FIG. 3 except that elapsed time is used instead of temperature.

  In FIG. 6, the processing of FIG. 3 is changed except that the processing of step S <b> 602 is changed to the elapsed time after applying a voltage to the CCD 10_41 (that is, the elapsed time after power-on) so that Table 2 can be referred to. The same processing is performed.

  Even if it does in this way, the big merit that the effect equivalent to having provided the temperature sensor can be acquired, and also cost reduction can be aimed at.

  As described above, it is possible to realize an imaging apparatus capable of reliably performing appropriate luminance adjustment and appropriate color tone adjustment regardless of the temperature environment.

It is the external appearance perspective view which looked at the digital camera 10 which is one Embodiment of the imaging device of this invention from diagonally upward. It is a block diagram which shows the circuit structure of the digital camera 10 shown in FIG. It is a figure explaining the difference of the black level between the area | region of a CCD where a light receiving sensor does not exist, and the area | region where a light receiving sensor exists. It is a flowchart which shows the procedure of the process which CPU10_47 performs. It is a figure explaining 2nd Embodiment. It is a flowchart which shows the procedure of the process which CPU10_47 shown in FIG. 5 performs.

Explanation of symbols

10 digital camera 10_4 release button 10_4A first contact 10_4B second contact 10_41 CCD
10_42 A / D conversion circuit 10_43 Image input controller 10_44 Image signal processing circuit 10_45 Compression processing circuit 10_47 CPU
10_470 Program memory 10_50 AE detection circuit 10_51 Memory (correction table)
10_53 recording unit 10_54 recording medium

Claims (4)

In an imaging device for generating an image signal by forming a subject image on an imaging device in which a large number of light receiving sensors are two-dimensionally arranged,
The imaging device has a black level detection region in which a light receiving sensor is not present and can be read from the region,
A black level detection unit that reads the black level detection region and generates a correction signal representing the black level;
An image signal processing unit that corrects a signal read from the light receiving sensor on the image sensor with a correction signal generated by the black level detection unit;
A temperature detector for detecting the temperature,
The black level detector generates a correction signal corresponding to the temperature detected by the temperature detector. A sensitivity setting section is provided to set the shooting sensitivity.
The said black level detection part produces | generates the correction signal according to the sensitivity set by the said sensitivity setting part while responding to the temperature detected by the said temperature detection part. Shooting device. In an imaging device for generating an image signal by forming a subject image on an imaging device in which a large number of light receiving sensors are two-dimensionally arranged,
The imaging device has a black level detection region in which a light receiving sensor is not present and can be read from the region,
A black level detection unit that reads the black level detection region and generates a correction signal representing the black level;
An image signal correction unit that corrects a signal read from the light receiving sensor on the image sensor with a correction signal generated by the black level detection unit;
It has a time measurement unit that measures the elapsed time after power on,
The black level detecting unit generates a correction signal corresponding to the time measured by the time measuring unit. A sensitivity setting section is provided to set the shooting sensitivity.
The said black level detection part produces | generates the correction signal according to the sensitivity set by the said sensitivity setting part while responding to the time measured by the said time measurement part. Shooting device.

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