JP2008219803A - Image signal correction method and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily and surely correct an image signal so as to eliminate an image step caused by dividing an image region even in a case where there is the effect of shading, etc., by using a contrast evaluation value. <P>SOLUTION: Offset of an image signal is corrected for performing black level adjustment of the image signal for each imaging region and a gain of the image signal is then corrected for adjusting an output value of the image signal for each imaging region, thereby removing the image step caused by an output difference of the image signal for each imaging region. The gain correction is herein performed by correcting the gain of at least one of image signals read out separately for each imaging region such that a contrast evaluation value calculated from an image signal in a measuring region of the contrast evaluation value set to be spread over divided imaging regions becomes equal to or lower than a predetermined threshold, when an object without contrast is photographed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image signal correction method and an image pickup apparatus, and more particularly to an image signal correction method and an image pickup apparatus for correcting a signal level difference when a multi-line reading CCD is used.

  With the increase in the number of pixels of an image sensor such as a CCD (Charge Coupled Device), it takes a long time to read pixel data acquired by the image sensor from the image sensor. For this reason, there is a problem in that the time lag at the time of shooting increases, and the operability as a camera deteriorates.

  As a countermeasure, a method of shortening the readout time by increasing the number of clocks for reading out the image signal from the CCD is taken, but problems such as an increase in noise occur. Has reached.

  For this reason, attempts have been made to branch the CCD readout into two and simultaneously read out to speed up the readout time. However, in the case of reading the image signal by dividing the image sensor into two regions, an analog gain amplifier or the like is used. Due to the variation in characteristics, a step is generated in the divided portion of the area of the image sensor.

  In order to cope with this, Japanese Patent Laid-Open No. 2004-228561 discloses that each of the imaging pixels is based on the average value of the output of the dummy pixels that are arranged in each imaging area and output an image signal indicating black. There has been proposed an image signal correction method for correcting a density difference for each imaging region due to a difference in characteristics of an amplifier or the like by correcting a signal output of the region.

  Further, in Patent Document 2, a monitoring area adjacent to each other between the left and right imaging areas is provided, a signal level difference between the left and right monitoring areas is detected, and a correction value for the level difference is calculated. An imaging apparatus has been proposed in which an image signal is multiplied by a correction value so that there are no steps in the images of the left and right imaging areas.

In Patent Document 3, the signal level of each imaging region is matched to the same brightness by correcting and converting the signal level of each imaging region to a predetermined linearity based on the result of reading the white plate and the gray reference plate. Thus, there has been proposed an imaging apparatus that corrects a signal level difference.
JP 2003-250092 A JP 2003-259224 A Japanese Patent Laid-Open No. 2002-218186

  However, in the image signal correction methods described in Patent Documents 1 to 3, the signal level (integrated value) output for each image region is compared to correct the gain and the like, but based on only the integrated value. When the image signal is corrected, there is a problem that a step is generated in the image due to the influence of shading of a lens or the like. Hereinafter, the reason why a step is generated at the boundary between the left and right image areas due to the influence of shading or the like will be described with reference to FIG.

  As shown in FIG. 10A, a line L that crosses the imaging area divided into two imaging areas of the left imaging area and the right imaging area by the dividing line set at the center of the imaging area. When set, the signal level on the line L is as shown in FIG.

  The position indicating the maximum value of the signal level on the line L is on the right side of the position of the dividing line due to the influence of the shading of the lens. When the areas Al and Ar are set in the left imaging area and the right imaging area so as to be line-symmetric with respect to the dividing line, the position indicating the maximum value of the signal level in the line L is in the area Ar. The integrated value of the image signal in the area Ar becomes higher than the integrated value of the image signal in the area Al.

  For this reason, when the image signal is corrected so that the integrated value of the image signal in the region Al and the integrated value of the image signal in the region Ar coincide with each other, the image signal in the left imaging area becomes higher than the image signal in the right imaging area. There is a step in the image at the position of the dividing line between the area and the right imaging area.

  The present invention has been made in view of such circumstances. By using a contrast evaluation value, an image signal is eliminated so as to eliminate a step in an image due to the division of an image region even when there is an influence of shading or the like. An object of the present invention is to provide an image signal correction method and an image pickup apparatus that can easily and reliably correct the image.

  The image signal correction method according to claim 1 is an image signal that is read out separately for each imaging region from an imaging device having an imaging region divided into left and right or up and down to achieve the object, In the image signal correction method for correcting the output of the image signal for each imaging region so as to remove the image step due to the output difference of the image signal for each imaging region, the black level adjustment of the image signal for each imaging region is performed. For this purpose, the method includes: correcting the offset of the image signal; and correcting the gain of the image signal in order to correct the output value of the image signal for each imaging region, The step of performing the gain correction is to measure a contrast evaluation value measurement region that is set so as to photograph a subject without contrast and straddle the divided imaging region at the time of the photographing. An image signal is extracted from the extracted image signal, and a contrast evaluation value corresponding to the level difference of the image signal at the boundary of the divided imaging region is calculated from the extracted image signal, and the calculated contrast evaluation value is equal to or less than a predetermined threshold value. As described above, the gain of at least one of the image signals read out separately from the divided imaging regions is corrected.

  According to the image signal correction method of the first aspect, the offset of the image signal is corrected in order to adjust the black level of the image signal for each imaging region, and then the output value of the image signal for each imaging region is corrected. By correcting the gain of the image signal for adjustment, the output of the image signal for each imaging region is corrected, and the level difference of the image due to the output difference of the image signal for each imaging region is removed. Note that the gain correction is performed by calculating a contrast evaluation value using an image signal extracted from the measurement area of the contrast evaluation value that is set so as to straddle the divided imaging areas when a subject without contrast is photographed. Then, it is performed by correcting the gain of at least one of the image signals read out separately from the imaging regions divided so that the contrast evaluation value is equal to or less than a predetermined threshold.

  As a result, the step due to the division of the image area can be reliably eliminated (not visible). That is, since the image signal is corrected using the contrast evaluation value of the subject (plant in which the high frequency component is detected), the image signal can be corrected without being conscious of shading or the like. In addition, since the image signal is corrected so that the contrast evaluation value is equal to or less than a predetermined threshold value, a step due to the division of the image region can be surely eliminated (not visible).

  The image signal correction method according to claim 2 is the image signal correction method according to claim 1, wherein the step of correcting the offset of the image signal is performed for each of the divided imaging regions of the imaging element. An offset of at least one of the image signals read out separately from the divided imaging areas so that the signals are read out separately from the provided OB areas and the integrated values of the separately read out signals match. It is characterized by correcting.

  According to the image signal correcting method of the second aspect, signals are read out separately from the OB area provided for each of the divided imaging areas of the imaging element. Then, the image signal for each imaging region is corrected by correcting the offset of at least one of the image signals separately read out from the divided imaging regions so that the integrated values of the signals read out separately match. Adjust the black level.

  Thereby, the black level can be easily adjusted.

  The image signal correction method according to claim 3 is the image signal correction method according to claim 1, wherein the step of correcting the offset of the image signal is performed in a state where the image sensor is shielded from light. A signal is separately read from a predetermined effective pixel area provided for each of the divided imaging areas of the imaging element, and separately from the divided imaging areas so that the integrated values of the separately read signals match. The offset of at least one of the read image signals is corrected.

  According to the method for correcting an image signal according to claim 3, shooting is performed in a state where the image sensor is shielded from light, and signals are separately read out from predetermined effective pixel areas provided for each of the divided image areas of the image sensor. . Then, the image signal for each imaging region is corrected by correcting the offset of at least one of the image signals separately read out from the divided imaging regions so that the integrated values of the signals read out separately match. Adjust the black level.

  As a result, the black level can be adjusted with higher accuracy by using the image signal of the effective pixel region that is used when an image is actually created.

  The image signal correction method according to claim 4 is the image signal correction method according to any one of claims 1 to 3, wherein the image sensor outputs R, G, and B image signals. The offset correction and the gain correction are performed for each of the R, G, and B image signals.

  The image signal correction method according to claim 5 is the image signal correction method according to claim 4, wherein the step of correcting the offset of the image signal is a predetermined one of R, G, and B. The offset of the R, G, B analog image signal is corrected based on the analog image signal of R, and the corrected R, G, B analog image signal is converted into the R, G, B digital image signal. Converting, separately correcting the offset of the digital image signals of two colors other than the predetermined one of the converted R, G, B digital image signals, and correcting the gain of the image signal The performing step corrects the gain of the analog image signal of R, G, B based on the analog image signal of a predetermined color of R, G, B, and the corrected R, G, B Analog image signal R, G, B digital It converted into the image signal, the converted R, characterized in that G, corrected separately the gain of the two colors of the digital image signal of other than the predetermined one color of the digital image signal of B.

  According to the image signal correcting method of claim 5, the offset of the R, G, B analog image signal is corrected based on the analog image signal of a predetermined color of R, G, B. The corrected R, G, and B analog image signals are converted into R, G, and B digital image signals, and the predetermined one of the converted R, G, and B digital image signals The offset of the image signal is corrected by separately correcting the offsets of the digital image signals of the other two colors. Thereafter, the gain of the R, G, B analog image signal is corrected based on the analog image signal of a predetermined color of R, G, B, and the corrected R, G, B analog image is corrected. The signals are converted into R, G, B digital image signals, and the gains of the digital image signals of two colors other than the predetermined one of the converted R, G, B digital image signals are separately obtained. Thus, the gain of the image signal is corrected. That is, offset correction and gain correction are performed on all R, G, and B image signals in the analog signal before A / D conversion, and for each R, G, and B image signal in the analog signal after A / D conversion. Perform offset correction and gain correction.

  Thereby, offset correction and gain correction can be performed with high accuracy.

  The imaging device according to claim 6 has an imaging area divided into left and right or upper and lower sides, an image sensor capable of reading out an image signal for each imaging area, and each image sensing area of the image sensor. Gain correction means for separately correcting the gain of the image signal, offset correction means for separately correcting the offset of the image signal corrected by the gain correction means, and the image signal corrected by the offset correction means. Control means for controlling the offset correction means and the gain correction means so as to remove a step at the boundary of the divided imaging area, and the control means is configured to divide the divided imaging area at the time of photographing an object having no contrast. Extracting means for extracting an image signal from a measurement region of a contrast evaluation value set so as to straddle, and whether the extracted image signal A calculation unit that calculates a contrast evaluation value according to a step of the image signal at the boundary between the divided imaging regions, and a gain of each image signal is separately set so that the calculated contrast evaluation value is equal to or less than a predetermined threshold value. And a gain level adjusting means for adjusting the gain level of at least one of the gain correcting means for correcting the gain.

  According to the imaging device according to claim 6, an imaging device capable of reading an image signal for each imaging region divided into left and right or top and bottom, and a gain of the image signal read from each imaging region of the imaging device. A gain correction unit that separately corrects the offset, an offset correction unit that separately corrects the offset of the gain-corrected image signal, and a step at the boundary between the divided imaging regions of each of the offset-corrected image signals. Control means for controlling the offset correction means and the gain correction means. In addition, the control unit includes an extraction unit that extracts an image signal from a measurement region of a contrast evaluation value that is set so as to straddle an imaging region that is divided at the time of shooting an object with no contrast, and a division from the extracted image signal Calculating means for calculating a contrast evaluation value corresponding to the step of the image signal at the boundary of the imaged area, and separately correcting the gain of each image signal so that the calculated contrast evaluation value is equal to or less than a predetermined threshold value Gain level adjusting means for adjusting the gain level of at least one of the gain correcting means.

  As a result, the step due to the division of the image area can be reliably eliminated (not visible). That is, since the image signal is corrected using the contrast evaluation value of the subject (plant in which the high frequency component is detected), the image signal can be corrected without being conscious of shading or the like. In addition, since the image signal is corrected so that the contrast evaluation value is equal to or less than a predetermined threshold value, a step due to the division of the image region can be surely eliminated (not visible).

  The image pickup apparatus according to claim 7 is the image pickup apparatus according to claim 6, wherein the control means separately reads signals from an OB area provided for each of the divided image pickup areas of the image pickup device. , At least one of the integration unit that integrates the separately read signals and the offset correction unit that separately corrects the offset of each image signal so that the integration values respectively integrated by the integration unit match. And an offset level adjusting means for adjusting the offset level of the offset correcting means.

  According to the imaging device according to claim 7, means for separately reading a signal from the OB area provided for each of the divided imaging areas of the imaging element, an integrating means for respectively integrating the separately read signals, An offset level adjusting means for adjusting an offset level of at least one of the offset correcting means for separately correcting the offset of each image signal so that the integrated values respectively integrated by the integrating means match, The control means offset-corrects the image signal that has been gain-corrected so as to remove a step at the boundary of the imaging region.

  Thereby, the black level can be easily adjusted.

  An imaging apparatus according to an eighth aspect of the present invention is the imaging apparatus according to the sixth aspect, further comprising light shielding means for shielding light incident on the imaging element, wherein the control means shields the imaging element by the light shielding means. Means for taking a picture in a state and reading the signals separately from a predetermined effective pixel area provided for each of the divided imaging areas of the imaging device, integrating means for integrating the separately read signals, and the integration Offset level adjusting means for adjusting the offset level of at least one of the offset correction means for separately correcting the offset of each image signal so that the integrated values respectively integrated by the means match. It is characterized by that.

  According to the image pickup apparatus of the eighth aspect, the image pickup device is provided for each of the divided image pickup regions of the image pickup device after the image pickup is performed in a state where the image pickup device is blocked by the light blocking unit that blocks light incident on the image pickup device. Means for reading out signals separately from the predetermined effective pixel area, integration means for integrating the separately read signals, and offsets of the respective image signals so that the integrated values respectively integrated by the integration means match. The offset level adjusting means for adjusting the offset level of at least one of the offset correcting means for separately correcting the image, and the control means gain-corrected image so as to remove the step at the boundary of the imaging region Offset correction of the signal.

  As a result, the black level can be adjusted with higher accuracy by using the image signal of the effective pixel region that is used when an image is actually created.

  The image pickup apparatus according to claim 9 is the image pickup apparatus according to any one of claims 6 to 8, wherein the image pickup element is a color image pickup element that outputs R, G, and B image signals, and the offset correction is performed. The means performs offset correction for each of the R, G, and B image signals, and the gain correction means performs gain correction for each of the R, G, and B image signals.

  An imaging apparatus according to a tenth aspect is the imaging apparatus according to the ninth aspect, wherein the offset correction unit includes a first offset correction unit that corrects an offset of an analog image signal of R, G, and B; , G and B digital image signals, and second offset correction means for separately correcting the offsets of the digital image signals of two predetermined colors, and the gain correction means includes the first offset A first gain correction unit that corrects the gain of the R, G, and B analog image signals corrected by the correction unit, and an R, G, and B digital image signal that is corrected by the first offset correction unit. Second gain correction means for separately correcting the gains of the digital image signals of the two predetermined colors, and the control means other than the predetermined two colors of R, G, and B of R, G, B images corrected by the first offset correction means and the first gain correction means by controlling the first offset correction means and the first gain correction means based on the color image signal. The second offset correction unit and the second gain correction unit are controlled based on the predetermined two color image signals of the signals.

  According to the imaging device of claim 10, first, in the first offset correction unit, R, G, and R based on an image signal of one color other than the predetermined two colors of R, G, and B. The offset of the B analog image signal is corrected, and then, in the second offset correction unit, the predetermined two colors of the R, G, B digital image signals corrected by the first offset correction unit are corrected. The control means corrects the offset of the image signal by separately correcting the offset of the digital image signal. The first gain correction unit corrects the gain of the R, G, and B analog image signals corrected by the first offset correction unit, and then the second gain correction unit performs the first offset. The control unit corrects the gain of the image signal by separately correcting the gains of the digital image signals of two predetermined colors among the R, G, and B digital image signals corrected by the correction unit.

  Thereby, offset correction and gain correction can be performed with high accuracy.

  An imaging apparatus according to an eleventh aspect is the imaging apparatus according to any one of the sixth to tenth aspects, wherein a contrast evaluation value calculating unit calculates a contrast evaluation value based on an image signal of an AF area obtained from the imaging element. And contrast AF means for controlling the focus lens so that the contrast evaluation value is maximized, and the contrast evaluation value calculation means also serves as the calculation means.

  According to the imaging apparatus of claim 11, the calculating unit that calculates the contrast evaluation value according to the level difference of the image signal at the boundary of the imaging region divided from the image signal extracted from the measurement region of the contrast evaluation value. The contrast evaluation value calculating means for calculating a contrast evaluation value serving as a reference for performing contrast AF is also used.

  As a result, it is possible to calculate a contrast evaluation value corresponding to the step of the image signal at the boundary of the imaging region divided by the same method as in contrast AF. As a result, the step due to the division of the image region can be easily performed. Can be lost (not visible).

  According to the present invention, by using the contrast evaluation value, even when there is an influence such as shading, the image signal is easily and reliably corrected so as to eliminate the image step due to the division of the image area. be able to.

  The best mode for carrying out a method of correcting an image signal and an imaging apparatus according to the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing an electrical configuration of an imaging apparatus according to the present invention. This imaging apparatus is a digital camera that converts a captured image into a digital signal, records the image on a recording medium, and reproduces the image recorded on the recording medium.

  The digital camera 1 mainly includes an image sensor (CCD) 10, an AFE 11, a zoom lens 12, an aperture 13, a focusing lens 14, a mechanical shutter 15, a flash control circuit 16, a flash 17, a DSP 20 (central processing unit (CPU) 21, AF Detection circuit 22, AE / AWB detection circuit 23, memory (SDRAM) 24, media controller 25, FROM 26, image input controller 27, image signal processing circuit 28, compression processing circuit 29, LCD controller 30), LCD 31, recording medium 32, The camera / playback switch 37, a mode dial 38, a shutter button 39, and the like are included.

  The CCD 10 is composed of, for example, a color CCD having a predetermined color filter array, and electronically captures an image of a subject formed by the zoom lens 12 and the focusing lens 14. The CCD 10 is driven based on a timing signal output from a timing generator (TG) in response to a command from the CPU 21.

  FIG. 2 is a schematic plan view showing a schematic configuration of the CCD 10.

  The CCD 10 is a two-dimensional imaging device (image sensor) in which a large number of photodiodes (light receiving cells) are arranged in a horizontal array (row direction) and a vertical direction (column direction) with a constant arrangement period. An effective pixel region that is not shielded, an optical black region (OB (optical black) area) in which a light receiving cell disposed at the lower end of the effective pixel region is shielded, a horizontal transfer path (horizontal CCD), an output unit, It consists of

  A vertical transfer path (vertical CCD) is provided at the side of each light-receiving cell in the effective pixel area and the OB area, and the charge accumulated in each light-receiving cell is transferred to the vertical CCD when the CCD is driven, and further the vertical CCD. The upper charges are sequentially transferred downward in FIG. A horizontal transfer path (horizontal CCD) is provided below the effective pixel area and the OB area, and charges on the horizontal CCD are sequentially transferred in the horizontal direction by being driven in two phases.

  The effective pixel area, the OB area, and the horizontal CCD are divided into left and right at the center. That is, the effective pixel area is divided into a left imaging area and a right imaging area, and the OB area is divided into a left OB area and a right OB area. The horizontal CCD receives a signal charge for one line sequentially transferred from the left imaging area and the left OB area, and a signal for one line sequentially transferred from the right imaging area and the right OB area. It is divided into a right horizontal CCD that receives electric charges. The final stages of the left horizontal CCD and the right horizontal CCD are connected to output units (left output unit and right output unit) each including an output amplifier.

  The left output unit and the right output unit detect the charge of the input signal charge and output it as a signal voltage, thereby outputting a signal photoelectrically converted by each light receiving cell as a dot-sequential signal string. The output signal is input to the AFE 11.

  The AFE 11 is mainly composed of a CDS circuit, an analog amplifier, and an A / D conversion circuit. The image signal output from the image sensor 10 is subjected to sampling hold (correlated double sampling processing) for each pixel in the CDS circuit, and then amplified by an analog amplifier (AGC) for A / Output to D conversion circuit. The A / D conversion circuit converts the analog R, G, B signals output from the AFE 11 into digital R, G, B signals, and outputs them to the image input controller 27 in the DSP 20.

  The DSP 20 includes a central processing unit (CPU) 21, an AF detection circuit 22, an AE / AWB detection circuit 23, a memory (SDRAM) 24, a media controller 25, a FROM 26, an image input controller 27, an image signal processing circuit 28, and a compression processing circuit 29. , An LCD controller 30 and an LCD 31.

  The CPU 21 performs overall control of each circuit in the digital camera 1 when an operation signal is input from the shooting / playback changeover switch 37, the mode dial 38, and the like, and executes processing according to the camera control program. The CPU 21 is connected to the bus and exchanges necessary data with the SDRAM 24 and the FROM 26.

  The AF detection circuit 22 includes a high-pass filter that passes only high-frequency components of the G signal, an absolute value processing unit, an AF area detection unit that extracts a signal within a predetermined focus area (for example, the center of the screen), and an absolute value within the AF area. It consists of an integration unit that integrates value data.

  The AE / AWB detection circuit 23 calculates a physical quantity necessary for AE control and AWB control from the input image signal in accordance with a command from the CPU 21. For example, as a physical quantity required for AE control, one screen is divided into a plurality of areas (for example, 16 × 16), and an integrated value of R, G, and B image signals is calculated for each divided area.

  The SDRAM 24 is used as a calculation work area for the CPU 21 and also as a temporary storage area for image data and the like.

  The media controller 25 controls reading / writing of data with respect to the recording medium 32 loaded in the digital camera 1 in accordance with a command from the CPU 21.

  The FROM 26 stores various parameters relating to camera control such as a camera control program and defect information of the solid-state imaging device. The CPU 21 develops the camera control program stored in the FROM 26 in the SDRAM 24, and executes various processes while using the SDRAM 24 as a work memory.

  The image input controller 27 outputs digital R, G, B signals output from the AFE 11 to the SDRAM 24.

  The image signal processing circuit 28 includes a synchronization circuit (a processing circuit that converts a color signal into a simultaneous expression by interpolating a spatial shift of the color signal associated with the color filter array of a single CCD), a white balance correction circuit, and a gamma correction. A circuit, a contour correction circuit, a luminance / color difference signal generation circuit, etc., and according to a command from the CPU 21, the SDRAM 24 is used to perform necessary signal processing on the input image signal to obtain luminance data (Y data) and color difference Image data (YUV data) composed of data (Cr, Cb data) is generated.

  The compression processing circuit 29 performs compression processing of a predetermined format on the input image data in accordance with a command from the CPU 21 to generate compressed image data. Further, in accordance with a command from the CPU 21, the input compressed image data is subjected to a decompression process in a predetermined format to generate non-compressed image data.

  The LCD controller 30 controls display on the LCD 31 in accordance with a command from the CPU 21. That is, in accordance with a command from the CPU 21, the input image signal is converted into a video signal (for example, NTSC signal, PAL signal, SCAM signal) for display on the LCD 31 and output to the LCD 31, and predetermined character and graphic information is also displayed. Is output to the LCD 31.

  The LCD 31 is a liquid crystal display capable of color display. The LCD 31 is used as an image display panel for displaying a photographed image in the playback mode, and is also used as a user interface (GUI) display panel for performing various setting operations. In the photographing mode, a through image is displayed as necessary, and is used as an electronic viewfinder for checking the angle of view.

  The shooting / playback switch 37 is used to instruct switching to the playback mode. That is, the digital camera 1 is switched to the playback mode when the shooting / playback switch 37 is pressed during shooting. When the photographing / playback switching switch 37 is pressed with the power off, the digital camera 1 is activated in the playback mode.

  The mode dial 38 functions as shooting mode setting means for setting the shooting mode of the digital camera 1, and the shooting mode of the digital camera 1 is set to various modes depending on the setting position of the mode dial. For example, an “auto shooting mode” in which an aperture, a shutter speed, and the like are automatically set by the digital camera 1, a “movie shooting mode” in which a movie is shot, and a “face extraction shooting mode” in which a person's face is extracted and shot. `` Sports shooting mode '' suitable for moving body shooting, `` Scenery shooting mode '' suitable for landscape shooting, `` Night scene shooting mode '' suitable for shooting sunset and night scenes, shutter scale set by the photographer, shutter speed "Aperture priority shooting mode" in which the digital camera 1 is automatically set, the shutter speed is set by the photographer, and "Shutter speed priority shooting mode" in which the digital camera 1 automatically sets the aperture scale, the aperture and shutter “Manual shooting mode” or the like in which the photographer sets the speed or the like.

  The shutter button 39 is composed of a two-stroke switch composed of so-called “half press” and “full press”. When the shutter release button 39 is pressed halfway, the digital camera 1 performs shooting preparation processing, that is, each of AE (Automatic Exposure), AF (Auto Focus), and AWB (Automatic White Balance). When the image is processed and fully pressed, the image is captured and recorded.

  The zoom lens 12 is driven by a motor driver 33 controlled by the CPU 21, and performs focus control, zoom control, and the like.

  The diaphragm 13 is composed of a plurality of diaphragm blades. The diaphragm 13 is driven by a motor driver 34 controlled by the CPU 21 and adjusts the amount of incident image light from the subject.

  The focusing lens 14 is driven by a motor driver 35 controlled by the CPU 21 and is displaced in the optical axis direction to focus on the imaging surface of the CCD 10.

  The mechanical shutter 15 is driven by a motor driver 36 controlled by the CPU 21 and physically blocks light incident on the light receiving surface of the solid-state imaging device.

  When the amount of light received by the light control sensor (not shown) reaches a predetermined amount, the flash control circuit 16 cuts off the power supply to the flash 17 and stops the flash 17 from emitting light.

  The flash 17 is configured with, for example, a xenon tube as a light source, and is formed so that the amount of light emission can be adjusted. In addition to a xenon tube, a flash using a high-luminance LED as a light source can also be used.

  Next, photographing, recording operation, and reproduction operation of the digital camera 1 of the present embodiment configured as described above will be described.

  In this digital camera 1, when a power button (not shown) is turned on, the CPU 21 detects this, turns on the power in the camera, and enters a shooting standby state in the shooting mode.

  In this photographing standby state, the CPU 21 normally displays a moving image (through image) on the LCD 31 as follows.

  When the mechanical shutter 15 is opened and the zoom lens 12 and the focusing lens 14 are extended to predetermined positions, the through image is taken by the CCD 10 and the through image is displayed on the LCD 31. That is, images are continuously picked up by the CCD 10, and the image signals are continuously processed to generate image data for through images. The generated image data is sequentially added to the LCD controller 30, converted into a display signal format, and output to the LCD 31. As a result, the image captured by the CCD 10 is displayed through on the LCD 31.

  The photographer performs framing while viewing the through image displayed on the LCD 31, confirms the subject to be photographed, confirms the image after photographing, and sets photographing conditions.

  When the shutter button 39 is half-pressed in the shooting standby state, an S1 ON signal is input to the CPU 21. The CPU 21 detects this and performs AE metering and AF control. At the time of AE photometry, the brightness of the subject is measured based on the integrated value of the image signal taken in via the CCD 10 or the like. This photometric value (photometric value) is used to determine the aperture value of the aperture 13 and the shutter speed during actual photographing. At the same time, it is determined from the detected subject brightness whether the flash 17 needs to emit light. If it is determined that the flash 17 needs to emit light, the flash 17 is pre-lighted, and the light emission amount of the flash 17 at the time of actual photographing is determined based on the reflected light.

  When the shutter button 39 is fully pressed, an S2 ON signal is input to the CPU 21. The CPU 21 executes photographing and recording processing in response to the S2ON signal.

  First, the CPU 21 drives the aperture 13 via the motor driver 44 based on the aperture value determined based on the photometric value, and accumulates charges in the CCD 10 so that the shutter speed determined based on the photometric value is obtained. Control time (so-called electronic shutter).

  In addition, the CPU 21 sequentially moves the focus lens to a lens position corresponding to the distance from the nearest to infinity during the AF control, and the high frequency component of the image signal based on the image signal of the AF area captured via the CCD 10 for each lens position. An integrated evaluation value (AF evaluation value) is acquired, a lens position where the evaluation value reaches a peak (that is, the contrast becomes maximum) is obtained, and contrast AF is performed to move the focus lens to the lens position.

  The subject light is incident on the light receiving surface of the CCD 10 via the photographing lens including the focusing lens 14, the zoom lens 12, and the like, the diaphragm 13, the mechanical shutter 15, and the like.

  The CCD 10 is composed of a color CCD provided with R, G, B color filters in a predetermined color filter array (for example, honeycomb array, Bayer array), and the light incident on the light receiving surface of the CCD 10 Each photodiode arranged on the surface is converted into a signal charge in an amount corresponding to the amount of incident light. The signal charges accumulated in each photodiode are read according to the timing signal output from the timing generator (TG) in response to a command from the CPU 21, sequentially output from the CCD 10 as a voltage signal (image signal), and input to the AFE 11. Is done. In the present embodiment, since the image signal acquired in the left imaging area and the image signal acquired in the right imaging area are output from different output units, each image signal is input to the AFE 11 separately.

  The AFE 11 mainly includes a CDS circuit, an analog amplifier, and an A / D conversion circuit. The CDS circuit performs correlated double sampling processing on the CCD output signal based on the CDS pulse, and the analog amplifier is added from the CPU 21. The image signal output from the CDS circuit is amplified by the imaging sensitivity setting gain.

  The analog image signal output from the analog amplifier is converted into a digital image signal by an A / D conversion circuit, and the converted image signal (R, G, B RAW data) is converted into SDRAM 24 via a bus. To be stored once.

  The R, G, and B image signals read from the SDRAM 24 are input to the image signal processing circuit 28. In the image signal processing circuit 28, white balance adjustment is performed by applying digital gain to each of the R, G, and B image signals by the white balance adjustment circuit, and gradation conversion processing corresponding to the gamma characteristic is performed by the gamma correction circuit. In addition, a synchronization process is performed in which a color signal is converted into a simultaneous expression by interpolating a spatial shift of the color signal associated with the color filter array of the single CCD by the synchronization circuit. The synchronized R, G, B image signals are further converted into a luminance signal Y and color difference signals Cr, Cb (YC signal) by a luminance / color difference data generation circuit, and the Y signal is subjected to contour enhancement processing by a contour correction circuit. Is done. The YC signal processed by the image signal processing circuit 28 is stored in the SDRAM 24 again.

  The YC signal stored in the SDRAM 24 as described above is compressed by the compression processing circuit 29 and recorded on the recording medium 32 through the media controller 25 as an image file of a predetermined format. In the case of the digital camera 1 of this example, still image data is stored in the recording medium 32 as an image file according to the Exif standard. As the recording medium 32, an xD picture card (registered trademark) detachably attached to the digital camera 1, a semiconductor memory card represented by smart media (registered trademark), a portable small hard disk, a magnetic disk, an optical disk, a magneto-optical disk, etc. Various recording media can be used.

  The image data recorded on the recording medium 32 in this manner is reproduced and displayed on the LCD 31 by setting the mode of the digital camera 1 to the reproduction mode. Transition to the reproduction mode is performed by switching the photographing / reproduction switching switch 37.

  When the playback mode is selected, the image file of the last frame recorded on the recording medium 32 is read out via the media controller 25. The compressed data of the read image file is expanded into an uncompressed YC signal via the compression processing circuit 29.

  The decompressed YC signal is held in the SDRAM 24 (or a VRAM (not shown)), converted into a signal format for display by the LCD controller 30, and output to the LCD 31. As a result, the last frame image recorded on the recording medium 32 is displayed on the LCD 31. The image displayed on the LCD 31 is forwarded in the forward direction when a right key (not shown) is pressed, and forwarded in the reverse direction when the left key of the cross key is pressed. Then, the image file at the frame position where the frame is advanced is read from the recording medium 32, and the image is reproduced on the LCD 31 in the same manner as described above.

  In the image captured, recorded, and reproduced in this way, the left imaging area and the right imaging area are used because the left imaging area and the right imaging area use separate horizontal CCDs and image signals output from the output unit. Are different horizontal CCDs, and the image signal output from the output unit is used, the same conditions may occur due to differences in transfer efficiency between the left horizontal CCD and right horizontal CCD, differences in the amplifier characteristics of the output unit, etc. Even in the case of shooting at the position, a difference occurs in the image signals output from the left imaging area and the right imaging area. Therefore, there is a problem that a step is generated in an image obtained by synthesizing image signals obtained in the respective imaging areas.

  In order to solve such a problem, a contrast evaluation value (AF evaluation value) measurement area is set so as to straddle the left imaging area and the right imaging area, and each AF evaluation value in the contrast evaluation value measurement area is reduced. By correcting the image signal in the imaging area, the level difference of the image is eliminated, that is, the level difference of the image cannot be visually recognized. Hereinafter, a method for correcting an image signal using an AF evaluation value will be described.

<First Embodiment for Correcting Image Signal Using AF Evaluation Value>
In the first embodiment in which the image signal is corrected using the AF evaluation value, the gain is corrected using the AF evaluation value after the offset correction is performed using the integrated value of the image signal in the OB area. Is.

  FIG. 3 is a flowchart showing the flow of processing of the first embodiment for correcting an image signal using AF evaluation values. FIG. 4 is a block diagram showing the electrical configuration, and shows the flow of processing shown in FIG. The following processing is executed by the CPU 21.

  First, using the integrated value of the image signals in the OB area, offset correction is performed so that the left and right image signals have the same level (steps S1 to S19).

  An OB area for calculating the integrated value is set (step S1). As shown in FIG. 5, all of the left OB area and the right OB area arranged in the lower part of the imaging area may be used for the calculation of the integrated value, or a part of each of the left OB area and the right OB area is integrated. You may use for calculation of a value.

  When the OB area is set, offset correction using the G pixel is performed (steps S2 to S7). The reason why the offset correction using the G pixel is performed first is that the G pixel is closest to the luminance component. The offset correction at the G pixel is performed by the AFE 11, that is, performed on the analog signal.

  Shooting is performed with a target brightness level 64, which is an appropriate level of AE, and the image data is stored in the SDRAM 24 (step S2). Using the data stored in the SDRAM 24, the integrated value of G pixels in the OB area set in step S1 is calculated (step S3).

  It is determined whether the integrated value of the G pixel in the left OB area (left G pixel OB integrated value) is larger than the integrated value of the G pixel in the right OB area (right G pixel OB integrated value) (step S4).

  When the left G pixel OB integrated value is larger than the right G pixel OB integrated value (YES in step S4), correction for increasing the offset level on the right side of the AFE 11 is performed (step S5), and photographing at the luminance level 64 is performed again. (Step S2) is performed.

  If the left G pixel OB integrated value is not larger than the right G pixel OB integrated value (NO in step S4), it is determined whether the left G pixel OB integrated value is smaller than the right G pixel OB integrated value (step S6). ).

  When the left G pixel OB integrated value is smaller than the right G pixel OB integrated value (YES in step S6), correction is performed to reduce the offset level on the right side of the AFE 11 (step S7), and photographing at the luminance level 64 is again performed (step S7). Step S2) is performed.

  If the left G pixel OB integrated value is not smaller than the right G pixel OB integrated value (NO in step S6), the left G pixel OB integrated value and the right G pixel OB integrated value are equal to each other. The offset correction using is terminated.

  Thereby, the correction of the offset using the G pixel is completed.

  When the offset correction using the G pixel (steps S2 to S7) is completed, the offset correction using the R pixel (steps S8 to S13) and the offset correction using the B pixel (steps S14 to S19). Is done. Since the offset of the G pixel is corrected in the analog image signal, the offset of the R pixel and the B pixel other than the G pixel is corrected by the DSP 20, that is, the digital signal after A / D conversion.

  Shooting is performed with a target brightness level 64, which is an appropriate level of AE, and the image data is stored in the SDRAM 24 (step S8). Using the data stored in the SDRAM 24, the integrated value of R pixels in the OB area set in step S1 is calculated (step S9).

  It is determined whether the integrated value of the R pixel in the left OB area (left R pixel OB integrated value) is larger than the integrated value of the R pixel in the right OB area (right R pixel OB integrated value) (step S10).

  When the left R pixel OB integrated value is larger than the right R pixel OB integrated value (YES in step S10), correction is performed to increase the right offset level of the DSP 20 (step S11), and imaging at the luminance level 64 is performed again. (Step S8) is performed.

  If the left R pixel OB integrated value is not greater than the right R pixel OB integrated value (NO in step S10), it is determined whether the left R pixel OB integrated value is smaller than the right R pixel OB integrated value (step S12). ).

  When the left R pixel OB integrated value is smaller than the right R pixel OB integrated value (YES in step S12), correction is performed to decrease the right offset level of the DSP 20 (step S13), and photographing at the luminance level 64 is performed again (step S13). Step S8) is performed.

  If the left R pixel OB integrated value is not smaller than the right R pixel OB integrated value (NO in step S12), the left R pixel OB integrated value and the right R pixel OB integrated value are equal to each other. The correction of the offset is completed using, and the offset of the B pixel is corrected.

  Shooting is performed with the brightness level 64, which is an appropriate level of AE, as a target, and the image data is stored in the SDRAM 24 (step S14). Using the data stored in the SDRAM 24, the integrated value of B pixels in the OB area set in step S1 is calculated (step S15).

  It is determined whether or not the B pixel integrated value (left B pixel OB integrated value) in the left OB area is larger than the B pixel integrated value (right B pixel OB integrated value) in the right OB area (step S16).

  When the left B pixel OB integrated value is larger than the right B pixel OB integrated value (YES in step S16), correction is performed to increase the right offset level of the DSP 20 (step S17), and photographing at the luminance level 64 is performed again. (Step S14) is performed.

  If the left B pixel OB integrated value is not greater than the right B pixel OB integrated value (NO in step S16), it is determined whether the left B pixel OB integrated value is smaller than the right B pixel OB integrated value (step S18). ).

  When the left B pixel OB integrated value is smaller than the right B pixel OB integrated value (YES in step S18), correction is performed to reduce the right offset level of the DSP 20 (step S19), and the image is taken again at the luminance level 64 (step S19). Step S14) is performed.

  If the left B pixel OB integrated value is not smaller than the right B pixel OB integrated value (NO in step S18), the left B pixel OB integrated value and the right B pixel OB integrated value are equal to each other. The correction of the offset is completed using, and the offset of the B pixel is corrected.

  Thereby, the offset correction using the R pixel (steps S8 to S13) and the offset correction using the B pixel (steps S14 to S19) are completed. Since the offset correction is roughly performed by the offset correction using the analog signal using the G pixel, the offset fine adjustment may be performed on the digital signal of the R pixel and the B pixel.

  Thus, the offset correction (steps S1 to S19) is completed, and the black level adjustment is completed accordingly.

  Thereafter, the gain is corrected using the AF evaluation value (steps S20 to S50).

  The step of the image that occurs when the image signal is read out by dividing into the left imaging area and the right imaging area (left and right two-line reading) appears in the image as a step response. Therefore, the AF evaluation value increases as the step increases. growing. Conversely, if the step becomes smaller, the AF evaluation value becomes smaller. By paying attention to this AF evaluation value and correcting the left and right gains, it is possible to correct the left and right steps of the image.

  First, a contrast evaluation value measurement area for calculating an AF evaluation value is set (step S20). As shown in FIG. 5, the contrast evaluation value measurement area is set so as to straddle the left imaging area and the right imaging area, that is, to include a portion where an image level difference occurs. Note that any number of contrast evaluation value measurement areas may be set as long as the number is one or more.

  When the contrast evaluation value measurement area setting (step S20) is completed, the gain is corrected using the G pixel (steps S21 to S30). The reason why the gain is corrected first using the G pixel is that the G pixel is closest to the luminance component. The gain correction at the G pixel is performed by the AFE 11, that is, is performed on the analog signal.

  Shooting is performed with the brightness level 64, which is an appropriate level of AE, as a target, and the image data is stored in the SDRAM 24 (step S21). Using the data stored in the SDRAM 24, the AF evaluation value of the G pixel in the contrast evaluation value measurement area set in step S20 is calculated (step S22). The AF evaluation value is calculated using an IIR filter (high-pass filter) as shown in FIG. That is, when the G signal for each pixel is sequentially input to the AF detection circuit 22, a high frequency signal having a predetermined cutoff frequency or more is extracted by the IIR filter. The extracted high-frequency signal is digitally integrated, and the integrated value is output as an AF evaluation value.

  It is determined whether the AF evaluation value of the G pixel is smaller than a predetermined threshold (step S23). Here, the predetermined threshold is a value as close as possible to 0. If the AF evaluation value is equal to or lower than the predetermined threshold, it is considered that there is no level difference in the image, that is, the level difference in the image cannot be visually recognized. .

  If the AF evaluation value of the G pixel is not smaller than the predetermined threshold (NO in step S23), correction is performed to increase the gain level on the right side of the AFE 11 (step S24), and shooting at the luminance level 64 is performed. (Step S25). If the AF evaluation value of the G pixel is smaller than the predetermined threshold value (YES in step S23), the correction of the gain using the G pixel is ended.

  After shooting at the luminance level 64 and storing the image data in the SDRAM 24 (step S25), the AF evaluation value of the G pixel is calculated by the same method as in step S22 (step S26). It is determined whether the evaluation value is smaller than a predetermined threshold (step S27).

  If the AF evaluation value of the G pixel is not smaller than the predetermined threshold (NO in step S27), it is determined whether or not the AF evaluation value calculated in step S22 is larger than the AF evaluation value calculated in step S26. (Step S28).

  When the AF evaluation value calculated in step S22 is larger than the AF evaluation value calculated in step S26 (YES in step S28), correction for increasing the right gain level of the AFE 11 is performed (step S29). Then, photographing at the luminance level 64 is performed again (step S25). When the AF evaluation value calculated in step S22 is not larger than the AF evaluation value calculated in step S26 (NO in step S28), correction is performed to decrease the gain level on the right side of the AFE 11 (step S30). ) The image is taken again at the luminance level 64 (step S25).

  If the AF evaluation value of the G pixel is smaller than the predetermined threshold (YES in step S27), the correction of the gain using the pixel is ended.

  Thereby, the correction of the gain using the G pixel is completed.

  When the correction of the gain using the G pixel (steps S21 to S30) is completed, the correction of the gain using the R pixel (steps S31 to S40) and the correction of the gain using the B pixel (steps S41 to S50). Is done. Since the gain of the G pixel is corrected in the analog image signal, the gain of the R pixel and the B pixel other than the G pixel is corrected by the DSP 20, that is, the digital signal after A / D conversion.

  Shooting is performed with a target brightness level 64, which is an appropriate level of AE, and the image data is stored in the SDRAM 24 (step S31). Using the data stored in the SDRAM 24, the AF evaluation value of the R pixel in the contrast evaluation value measurement area set in step S20 is calculated (step S32). The AF evaluation value can be calculated by the same method as in step S22.

  It is determined whether or not the AF evaluation value of the R pixel is smaller than a predetermined threshold value (step S33). Here, the predetermined threshold is a value as close as possible to 0. If the AF evaluation value is equal to or lower than the predetermined threshold, it is considered that there is no level difference in the image, that is, the level difference in the image cannot be visually recognized. .

  When the AF evaluation value of the R pixel is not smaller than the predetermined threshold value (NO in step S33), correction is performed to increase the gain level on the right side of the DSP 20 (step S34), and shooting at the luminance level 64 is performed. (Step S35). If the AF evaluation value of the R pixel is smaller than the predetermined threshold (YES in step S33), the gain correction using the R pixel is ended.

  After shooting at the luminance level 64 and storing the image data in the SDRAM 24 (step S35), the AF evaluation value of the R pixel is calculated by the same method as in step S32 (step S36). It is determined whether the evaluation value is smaller than a predetermined threshold (step S37).

  If the AF evaluation value of the R pixel is not smaller than the predetermined threshold (NO in step S37), it is determined whether or not the AF evaluation value calculated in step S32 is larger than the AF evaluation value calculated in step S36. (Step S38).

  If the AF evaluation value calculated in step S32 is greater than the AF evaluation value calculated in step S36 (YES in step S38), correction is performed to increase the gain level on the right side of the DSP 20 (step S39). Then, photographing at the luminance level 64 is performed again (step S35). When the AF evaluation value calculated in step S32 is not larger than the AF evaluation value calculated in step S36 (NO in step S38), correction is performed to decrease the gain level on the right side of the DSP 20 (step S40). ) The image is taken again at the luminance level 64 (step S35).

  If the AF evaluation value of the R pixel is smaller than the predetermined threshold (YES in step S37), the gain correction using the R pixel is ended.

  When the correction of the gain using the R pixel (steps S31 to S40) is completed, shooting is performed targeting the luminance level 64, which is an appropriate level of AE, and the image data is stored in the SDRAM 24 (step S41). . The AF evaluation value of the B pixel in the contrast evaluation value measurement area set in step S20 is calculated using the data stored in the SDRAM 24 (step S42). The AF evaluation value can be calculated by the same method as in step S22.

  It is determined whether or not the AF evaluation value of the B pixel is smaller than a predetermined threshold (step S43). Here, the predetermined threshold is a value as close as possible to 0. If the AF evaluation value is equal to or lower than the predetermined threshold, it is considered that there is no level difference in the image, that is, the level difference in the image cannot be visually recognized. .

  If the AF evaluation value of the B pixel is not smaller than the predetermined threshold (NO in step S43), correction is performed to increase the gain level on the right side of the DSP 20 (step S44), and shooting at the luminance level 64 is performed. (Step S45). If the AF evaluation value of the B pixel is smaller than the predetermined threshold (YES in step S43), the gain correction using the B pixel is ended.

  After shooting at the luminance level 64 and storing the image data in the SDRAM 24 (step S45), the AF evaluation value of the B pixel is calculated by the same method as in step S42 (step S46). It is determined whether the evaluation value is smaller than a predetermined threshold (step S47).

  If the AF evaluation value of the B pixel is not smaller than the predetermined threshold (NO in step S47), it is determined whether or not the AF evaluation value calculated in step S42 is larger than the AF evaluation value calculated in step S46. (Step S48).

  If the AF evaluation value calculated in step S42 is larger than the AF evaluation value calculated in step S46 (YES in step S48), correction is performed to increase the gain level on the right side of the DSP 20 (step S49). Then, photographing at the luminance level 64 is performed again (step S45). When the AF evaluation value calculated in step S42 is not larger than the AF evaluation value calculated in step S46 (NO in step S48), correction is performed to decrease the gain level on the right side of the DSP 20 (step S50). ) The image is taken again at the luminance level 64 (step S45).

  When the AF evaluation value of the B pixel is smaller than the predetermined threshold (YES in step S47), the gain correction using the B pixel is ended. Since the gain is roughly corrected by correcting the gain with the analog signal using the G pixel, the gain fine adjustment may be performed on the digital signal of the R pixel and the B pixel.

  Thus, the gain correction (steps S20 to S50) is completed.

<Second Embodiment for Correcting Image Signal Using AF Evaluation Value>
In the second embodiment in which the image signal is corrected using the AF evaluation value, the AF evaluation value is corrected after the offset correction is performed using the integrated value of the image signal in the integrated value measurement area set in the imaging region. Is used to correct the gain.

  When correcting the offset so that the left and right integrated values are equal using the integrated value acquired in the imaging area when the light is blocked, the offset correction is performed using the integrated value of the OB area. However, since the image signal of the effective pixel region used when actually creating an image is used, there is an advantage that the black level can be adjusted with higher accuracy.

  FIG. 7 is a flowchart showing the flow of processing in the first embodiment for correcting an image signal using an AF evaluation value. FIG. 8 is a block diagram showing the electrical configuration, and shows the processing flow shown in FIG. The following processing is executed by the CPU 21. Note that the same portions as those in the first embodiment in which the image signal is corrected using the AF evaluation value are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 9, integrated value measurement areas are set in the left imaging area and the right imaging area, respectively, so as to be line-symmetric with respect to the dividing line set in the center of the imaging area (step S51). One or more integrated value measurement areas may be set in each imaging area of the left imaging area and the right imaging area. The integrated value measurement area is set so as not to cross the dividing line. Although FIG. 9 shows only the left imaging area and the right imaging area, an OB area may be provided below the imaging area.

  When the integrated value measurement area is set, offset correction using G pixels is performed (steps S52 to S57). The reason why the offset correction using the G pixel is performed first is that the G pixel is closest to the luminance component. The offset correction at the G pixel is performed by the AFE 11, that is, performed on the analog signal.

  Photographing is performed in a light-shielded state, and the image data is stored in the SDRAM 24 (step S2). Using the data stored in the SDRAM 24, the integrated value of G pixels for each integrated value measurement area set in step S51 is calculated (step S53).

  The integrated value of the G pixel in the integrated value measurement area set in the left imaging area (left G pixel integrated value) is the integrated value of the G pixel in the integrated value measurement area set in the right imaging area (right G pixel It is determined whether or not it is greater than (integrated value) (step S54).

  If the left G pixel integrated value is greater than the right G pixel integrated value (YES in step S54), correction is performed to increase the offset level on the right side of the AFE 11 (step S55), and imaging in the light-shielded state is performed again (step S52). ) Is performed.

  If the left G pixel integrated value is not larger than the right G pixel integrated value (NO in step S54), it is determined whether the left G pixel integrated value is smaller than the right G pixel integrated value (step S56).

  If the left G pixel integrated value is smaller than the right G pixel integrated value (YES in step S56), correction is performed to reduce the offset level on the right side of the AFE 11 (step S57), and imaging is performed again in a light-shielded state (step S52). Is done.

  If the left G pixel integrated value is not smaller than the right G pixel integrated value (NO in step S56), the left G pixel integrated value and the right G pixel integrated value are equal to each other. Offset correction is completed.

  Thereby, the correction of the offset using the G pixel is completed.

  When the offset correction using the G pixel (steps S52 to S57) is completed, the offset correction using the R pixel (steps S58 to S63) and the offset correction using the B pixel (steps S64 to S69). Is done. Since the offset of the G pixel is corrected in the analog image signal, the offset of the R pixel and the B pixel other than the G pixel is corrected by the DSP 20, that is, the digital signal after A / D conversion.

  Photographing is performed in a light-shielded state, and the image data is stored in the SDRAM 24 (step S58). Using the data stored in the SDRAM 24, the integrated value of R pixels for each integrated value measurement area set in step S51 is calculated (step S59).

  The R pixel integrated value (left R pixel integrated value) in the integrated value measurement area set in the left imaging area is the R pixel integrated value (right R pixel in the integrated value measurement area set in the right imaging area. It is determined whether or not it is greater than (integrated value) (step S60).

  If the left R pixel integrated value is larger than the right R pixel integrated value (YES in step S60), correction is performed to increase the offset level on the right side of the DSP 20 (step S61), and imaging in the light-shielded state is performed again (step S58). ) Is performed.

  If the left R pixel integrated value is not larger than the right R pixel integrated value (NO in step S60), it is determined whether the left R pixel integrated value is smaller than the right R pixel integrated value (step S62).

  When the left R pixel integrated value is smaller than the right R pixel integrated value (YES in step S62), correction is performed to reduce the right offset level of the DSP 20 (step S63), and the image is taken again in the light-shielded state (step S58). Is done.

  If the left R pixel integrated value is not smaller than the right R pixel integrated value (NO in step S62), the left R pixel integrated value and the right R pixel integrated value are equal to each other. Is completed, and the offset of the B pixel is corrected.

  Photographing is performed in a light-shielded state, and the image data is stored in the SDRAM 24 (step S64). Using the data stored in the SDRAM 24, the integrated value of the B pixel for each integrated value measurement area set in step S51 is calculated (step S65).

  The integrated value of B pixels (left B pixel integrated value) in the integrated value measurement area set in the left imaging area is the integrated value of B pixels (right B pixel in the integrated value measurement area set in the right imaging area) It is determined whether it is greater than (integrated value) (step S66).

  When the left B pixel integrated value is larger than the right B pixel integrated value (YES in step S66), correction is performed to increase the right offset level of the DSP 20 (step S67), and photographing in the light-shielded state is performed again (step S64). ) Is performed.

  If the left B pixel integrated value is not larger than the right B pixel integrated value (NO in step S66), it is determined whether the left B pixel integrated value is smaller than the right B pixel integrated value (step S68).

  If the left B pixel integrated value is smaller than the right B pixel integrated value (YES in step S68), correction is performed to decrease the right offset level of the DSP 20 (step S69), and the image is taken again in the light-shielded state (step S64). Is done.

  If the left B pixel integrated value is not smaller than the right B pixel integrated value (NO in step S68), the left B pixel integrated value and the right B pixel integrated value are equal to each other. Is completed, and the offset of the B pixel is corrected.

  Thus, the offset correction using the R pixel (steps S58 to S63) and the offset correction using the B pixel (steps S64 to S69) are completed. Since the offset correction is roughly performed by the offset correction using the analog signal using the G pixel, the offset fine adjustment may be performed on the digital signal of the R pixel and the B pixel.

  Thus, the offset correction (steps S51 to S69) is completed, and the black level adjustment is completed accordingly.

  Thereafter, the gain is corrected using the AF evaluation value (steps S20 to S50). The gain correction is the same as that in the first embodiment in which the image signal is corrected using the AF evaluation value, and thus detailed description thereof is omitted.

  As a result, variations in offset and gain for each of R, G, and B can be absorbed.

  According to the present embodiment, since the image signal is corrected using the contrast evaluation value corresponding to the level difference of the image signal at the boundary of the divided imaging region, that is, the AF evaluation value, without being conscious of shading or the like. The step of the image due to the division of the image area can be eliminated. Further, since the AF evaluation value can be calculated by the same method as that in contrast AF, the step of the image can be easily eliminated without using a new mechanism. Further, since the image signal is corrected so that the AF evaluation value is equal to or less than a predetermined threshold value, the level difference of the image can be reliably corrected (cannot be visually recognized).

  In this embodiment, a CCD having an OB area in which a large number of light receiving cells are arranged in a horizontal array (row direction) and a vertical direction (column direction) with a constant arrangement period is used. A CCD having an OB area that is not used may be used. As a result, the black level can be adjusted without being affected by light leakage from the light shielding film.

  In the present embodiment, the imaging region is divided into left and right, but it may be divided up and down, or may be divided into two or more.

1 is a block diagram illustrating an electrical configuration of an imaging apparatus (digital camera) to which the present invention is applied. It is a plane schematic diagram which shows schematic structure of CCD10 of the said digital camera. It is a flowchart which shows the flow of a process of 1st Embodiment which correct | amends an image signal using AF evaluation value of the said digital camera. It is a flowchart which shows the flow of a process of 1st Embodiment which correct | amends an image signal using AF evaluation value of the said digital camera. It is explanatory drawing which shows the flow of a process of 1st Embodiment which correct | amends an image signal using AF evaluation value of the said digital camera. It is explanatory drawing of the setting method of the contrast evaluation value measurement area of 1st Embodiment which correct | amends an image signal using AF evaluation value of the said digital camera. It is an example of the high pass filter which calculates AF evaluation value of 1st Embodiment which correct | amends an image signal using AF evaluation value of the said digital camera. It is a flowchart which shows the flow of a process of 2nd Embodiment which correct | amends an image signal using AF evaluation value of the said digital camera. It is a flowchart which shows the flow of a process of 2nd Embodiment which correct | amends an image signal using AF evaluation value of the said digital camera. It is explanatory drawing which shows the flow of a process of 1st Embodiment which correct | amends an image signal using AF evaluation value of the said digital camera. It is explanatory drawing of the setting method of the integrated value measurement area and contrast evaluation value measurement area of 1st Embodiment which correct | amends an image signal using AF evaluation value of the said digital camera. It is explanatory drawing explaining the reason why a level | step difference arises in the boundary of the image area of right and left which is a problem of the prior art.

Explanation of symbols

10: Image sensor (CCD), 11: AFE, 12: Zoom lens, 13: Aperture, 14: Focusing lens, 15: Mechanical shutter, 16: Flash control circuit, 17: Flash, 20: DSP, 21: Central processing unit (CPU), 22: AF detection circuit, 23: AE / AWB detection circuit, 24: Memory (SDRAM), 25: Media controller, 26: FROM, 27: Image input controller, 28: Image signal processing circuit, 29: Compression Processing circuit, 30: LCD controller, 31: LCD, 32: recording medium, 37: shooting / playback switch, 38: mode dial, 39: shutter button

Claims (11)

An image signal that is read out separately for each imaging region from an imaging device having an imaging region that is divided into left and right or up and down, so that a step of the image due to an output difference of the image signal for each imaging region is removed. In the image signal correction method for correcting the output of each image signal,
Correcting the offset of the image signal in order to adjust the black level of the image signal for each imaging region;
Correcting the image signal gain to correct the output value of the image signal for each imaging region;
With
The step of correcting the gain of the image signal includes:
Shoot a subject without contrast,
An image signal is extracted from the measurement area of the contrast evaluation value set so as to straddle the divided imaging area at the time of shooting,
Calculating a contrast evaluation value according to a step of the image signal at the boundary of the divided imaging region from the extracted image signal;
A gain of at least one of the image signals read out separately from the divided imaging regions is corrected so that the calculated contrast evaluation value is equal to or less than a predetermined threshold. Correction method. The step of correcting the offset of the image signal includes:
Read signals separately from the OB area provided for each of the divided imaging areas of the imaging element,
The offset of at least one of the image signals read out separately from the divided imaging regions is corrected so that the integrated values of the signals read out separately match. The correction method of the image signal of description. The step of correcting the offset of the image signal includes:
Taking a picture in a state where the image sensor is shielded from light, separately reading out signals from a predetermined effective pixel area provided for each of the divided imaging areas of the image sensor
The offset of at least one of the image signals read out separately from the divided imaging regions is corrected so that the integrated values of the signals read out separately match. The correction method of the image signal of description. The image sensor is a color image sensor that outputs R, G, and B image signals,
The image signal correction method according to claim 1, wherein the offset correction and the gain correction are performed for each of R, G, and B image signals. The step of correcting the offset of the image signal includes:
Correcting the offset of the analog image signal of R, G, B based on the analog image signal of a predetermined color of R, G, B;
Converting the corrected R, G, B analog image signals into R, G, B digital image signals;
Separately correcting offsets of digital image signals of two colors other than the predetermined one of the converted R, G, and B digital image signals;
The step of correcting the gain of the image signal includes:
Correcting the gain of the analog image signal of R, G, B based on the analog image signal of a predetermined color of R, G, B;
Converting the corrected R, G, B analog image signals into R, G, B digital image signals;
5. The image according to claim 4, wherein gains of digital image signals of two colors other than the predetermined one of the converted R, G, and B digital image signals are separately corrected. Signal correction method. An imaging device having an imaging region divided into left and right or up and down, and capable of reading image signals for each imaging region;
Gain correction means for separately correcting the gain of the image signal read from each imaging region of the image sensor;
Offset correction means for separately correcting the offset of the image signal corrected by the gain correction means;
Control means for controlling the offset correction means and the gain correction means so as to remove a step at the boundary of the divided imaging area of each image signal corrected by the offset correction means,
The control means includes
Extraction means for extracting an image signal from a measurement region of a contrast evaluation value set so as to straddle the divided imaging region when photographing a subject without contrast;
Calculating means for calculating a contrast evaluation value according to a step of the image signal at the boundary of the divided imaging region from the extracted image signal;
A gain level adjusting means for adjusting the gain level of at least one of the gain correcting means for separately correcting the gain of each image signal so that the calculated contrast evaluation value is equal to or less than a predetermined threshold;
An imaging apparatus comprising: The control means includes
Means for separately reading signals from an OB area provided for each of the divided imaging areas of the imaging element;
Integrating means for integrating the separately read signals;
An offset level adjusting means for adjusting the offset level of at least one of the offset correcting means for separately correcting the offset of each image signal so that the integrated values respectively integrated by the integrating means match;
The imaging apparatus according to claim 6, further comprising: A light shielding means for shielding light incident on the image sensor;
The control means includes
Means for taking a picture in a state where the image sensor is shielded from light by the light shielding means, and separately reading out signals from predetermined effective pixel areas provided for each of the divided imaging areas of the image sensor;
Integrating means for integrating the separately read signals;
An offset level adjusting means for adjusting the offset level of at least one of the offset correcting means for separately correcting the offset of each image signal so that the integrated values respectively integrated by the integrating means match;
The imaging apparatus according to claim 6, further comprising: The image sensor is a color image sensor that outputs R, G, and B image signals,
The offset correction means performs offset correction for each of the R, G, and B image signals,
The imaging apparatus according to claim 6, wherein the gain correction unit performs gain correction for each of the R, G, and B image signals. The offset correction unit includes a first offset correction unit that corrects an offset of an analog image signal of R, G, and B, and a digital image of two predetermined colors among the digital image signals of R, G, and B Second offset correction means for separately correcting the offset of the signal,
The gain correction means is corrected by the first gain correction means for correcting the gain of the R, G, and B analog image signals corrected by the first offset correction means, and the first offset correction means. Second gain correction means for separately correcting the gains of the digital image signals of the two predetermined colors among the R, G, and B digital image signals;
The control means controls the first offset correction means and the first gain correction means based on an image signal of one color other than the predetermined two colors of R, G, and B, and the first The second offset correction means and the second gain correction means based on the image signals of the two predetermined colors among the R, G, and B image signals corrected by the offset correction means and the first gain correction means. The imaging device according to claim 9, wherein the imaging device is controlled. Contrast evaluation value calculating means for calculating a contrast evaluation value based on an image signal of an AF area obtained from the image sensor;
Contrast AF means for controlling the focus lens so that the contrast evaluation value is maximized,
The imaging apparatus according to claim 6, wherein the contrast evaluation value calculation unit also serves as the calculation unit.

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