JP2006109046A - Imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging device which is high in pixel density capable of correct color unevenness resulting from a variation in transfer characteristics due to an increase in a pixel signal driving speed, and reproducing images of high quality. <P>SOLUTION: The imaging device is equipped with an imaging means which photoelectrically converts the optical image of an object into image signals, a drive control signal generating means which generates control signals of controlling the drive of the imaging means, a reference signal generating means which generates reference signals that are used by the drive control signal generating means, an image signal processing means which applies a prescribed processing to image signals, and a detection means which detects the output state of images formed on the basis of the image signals. The image signal processing means controls and varies the frequency of reference signals generated by the reference signal generating means on the basis of the detection result of the detection means. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an imaging apparatus such as a digital camera, and more particularly to an imaging apparatus capable of correcting color unevenness caused by transfer characteristics generated by an imaging element having a high pixel density.

  In an imaging device such as an electronic camera, a scanner, or a digital video camera, an optical image is converted into a digital image signal by a semiconductor integrated circuit represented by a CCD (Charge Coupled Device).

  In these imaging apparatuses, color unevenness may occur in the image signal output from the imaging device due to aberrations of the optical system such as spherical aberration of the lens and dark current generated in the imaging device. Color unevenness greatly affects image reproducibility and image quality, and hinders high-quality image formation. Therefore, the influence must be removed by operations such as correction. Various techniques for correcting color unevenness have been studied.

  Here, a general method for correcting color unevenness will be described. First, the pixel group provided in the image sensor is blocked in the horizontal direction (H direction) and the vertical direction (V direction). Each block includes a predetermined number of pixels. The average value of the color unevenness for each block is measured, the color unevenness correction coefficient for each block is calculated according to the amount of color unevenness, and this coefficient is stored in the storage unit of the imaging apparatus. Then, the color unevenness correction coefficient is read from the storage unit at the time of imaging, and the color unevenness is corrected by performing arithmetic processing using the color unevenness correction coefficient on the captured image signal.

In addition, there is a method of performing color unevenness correction by obtaining a color unevenness correction coefficient by simulation, and in order to perform color unevenness correction due to aberration of the optical system, a gain function for color unevenness correction is set by simulation. There are disclosed a method for performing correction, and a method for performing color unevenness correction by setting an offset function for color unevenness correction by simulation in order to perform color unevenness correction due to dark current of an image sensor. (For example, see Patent Document 1)
Japanese Patent Laid-Open No. 2002-185971 (see paragraph 0012, etc.)

  By the way, as the performance of digital cameras has improved, the performance of image sensors has been demanded to be high resolution and high definition. For example, the image pickup device when the electronic camera was first commercialized was mainly VGA (Video Graphics Array; number of pixels = 640 × 480 pixels), but recently, SXGA (Super Extended Graphics Array; pixels). Number = 1280 × 960 pixels) and 5 million pixel class image sensors.

  An image sensor with such a high pixel density can handle high-speed driving by increasing the frequency of the drive signal, but when the drive signal is increased in speed, a sufficient potential is not applied within the image sensor. As a result, the pixel signal is transferred. As a result, the transfer characteristics vary between the pixel signals, and the transfer characteristic variations generated between the pixel signals cause color unevenness. Color unevenness due to variations in transfer characteristics between image sensors occurs randomly on the imaging surface, so it is used to correct color unevenness caused by aberrations in the optical system and dark current in the image sensor. It was extremely difficult to correct color unevenness by simulation.

  In addition, for color unevenness caused by variations in transfer characteristics, color unevenness correction coefficients (gain and offset) are stored in advance for each pixel, and the color unevenness correction coefficient stored at the time of imaging is read to correct the image signal. However, it is troublesome to obtain a color unevenness correction coefficient including a gain and an offset for each pixel with respect to an image pickup device having a huge number of pixels exceeding 1 million pixels. For this purpose, an enormous storage capacity is required, which leads to a complicated and expensive imaging apparatus.

  In addition, since the above-described Patent Document 1 does not describe an image sensor with a high pixel of the SXGA class or higher, there is a problem of color unevenness caused by variation in transfer characteristics of an image signal generated by the image sensor with a high pixel. There was no suggestion. As described above, there is no established technology for solving the problem of uneven color caused by variations in pixel signal transfer characteristics due to an increase in drive signal speed in an image sensor having a high pixel count exceeding 1 million pixels. .

  The present invention has been made in view of the above problems, and is an image pickup apparatus using an image pickup device having a high pixel size exceeding 1 million pixels, and without causing the image pickup apparatus to be complicated and expensive. It is an object of the present invention to provide an imaging apparatus capable of correcting color unevenness caused by variations in transfer characteristics of pixel signals generated due to high-speed driving.

  The object is achieved by the invention described in any one of claims 1 to 5 below.

(Claim 1)
Imaging means for photoelectrically converting a subject light image into an image signal and capturing the image;
Drive control signal generating means for generating a control signal for controlling driving of the imaging means;
Reference signal generating means for generating a reference signal used in the drive control signal generating means;
Image signal processing means for performing predetermined processing on the image signal;
Detecting means for detecting an output state of an image formed based on the image signal,
The image signal processing means includes
Based on the detection result of the detection means,
An image pickup apparatus that controls the operation of the reference signal generation means so that the frequency of the reference signal generated by the reference signal generation means varies.

(Claim 2)
The imaging apparatus according to claim 1, wherein the image signal processing unit controls the operation of the reference signal generation unit so that the frequency of the reference signal is reduced.

(Claim 3)
The imaging apparatus according to claim 1, wherein the detection unit detects color unevenness generated in the image signal.

(Claim 4)
The imaging apparatus includes a CDS circuit that samples an image signal captured by the imaging unit,
The sampling signal used in the CDS circuit is generated and supplied by the drive control signal generating means,
The imaging apparatus according to claim 1, wherein the drive control signal generation unit supplies a sampling signal whose phase is changed based on a detection result of the detection unit to the CDS circuit.

(Claim 5)
Conversion means for converting the image signal captured by the imaging means into a luminance signal and a color difference signal;
5. The image signal processing unit according to claim 1, wherein the image signal processing unit corrects a conversion condition used by the conversion unit based on a set photographing sensitivity to form a color difference signal. The imaging device described.

(Claim 6)
The imaging device according to claim 1, wherein the detection by the detection unit is performed when the imaging device is adjusted.

  According to the first to third aspects of the present invention, the frequency of the reference signal formed by the reference signal generating means varies, for example, even if a problem such as color unevenness occurs in the image signal captured by the imaging means. By doing so, the frequency of the drive control signal is controlled, and image correction can be performed to eliminate problems caused in the image signal. In particular, for image pickup devices having a high pixel density exceeding 1 million pixels, it is possible to effectively correct and eliminate the color unevenness that has been a concern due to the increase in the CCD drive signal frequency, thereby achieving high-quality image reproduction. It was possible to provide a possible imaging device.

  According to the fourth aspect of the invention, in addition to the effect expressed in the first aspect, the sampling signal of the CDS circuit that samples the image signal captured by the imaging means is optimized by varying the phase. As a result, the above-described color unevenness correction is performed more effectively, and the problem of color unevenness caused by the transfer characteristics of the image sensor can be solved more reliably.

  According to the fifth aspect of the present invention, in addition to the effects found in the first and third aspects, color unevenness is generated in the image signal when shooting is performed under a high sensitivity condition such as ISO 400 or higher. Even if it occurs, the correction can be made when converting the image signal to the color difference signal, so that the generated color unevenness can be made inconspicuous.

  Furthermore, according to the invention described in claim 6, the color unevenness of the image signal generated according to the transfer characteristic of the image pickup means can be detected and adjusted by the detection means at the time of image pickup apparatus adjustment. Highly efficient color unevenness detection is now possible.

  As a specific embodiment of the imaging apparatus according to the present invention, a digital camera is typical, but a mobile phone with a camera, a scanner, a digital video camera, and the like are also included.

  The appearance of a digital camera, which is one of the representative embodiments of the imaging apparatus according to the present invention, will be described with reference to FIGS. FIG. 1A is a front view of a digital camera 1 according to the present invention, and FIG. 2A is a top view of the digital camera 1, and FIG. 2B is a side view. As shown in the figure, the digital camera 1 includes an imaging unit 2 and a camera body unit 3.

  The imaging unit 2 includes an imaging unit including a photographing lens including a macro zoom and a photoelectric conversion element such as a CCD, and an optical image of the subject (subject light image) is converted into an image signal (a charge signal obtained by photoelectric conversion at each pixel of the CCD). Image signal).

  A macro zoom lens 201 (to be described later) is provided inside the imaging unit 2, and an imaging circuit (not shown) including a CCD area sensor 202 (to be described later) is provided behind the location where the macro zoom lens 201 is provided. It has been.

  In the imaging unit 2, a light control circuit (not shown) including a light control sensor that receives reflected light from the subject of flash light is provided at an appropriate position.

  The camera body unit 3 includes an LCD display unit 6 including an LCD (Liquid Crystal Display), an EVF (Electronic View Finder) 7, and an external connection terminal 12 for connecting the digital camera 1 to a personal computer (not shown). The image signal captured by the imaging unit 2 is subjected to predetermined signal processing, image display on the LCD display unit 6 and EVF 7, image recording on a recording medium such as a memory card 13 described later, or personal Processing such as image transfer to a computer is performed.

  As shown in FIG. 1A, a flash 4 is provided at an appropriate position on the front surface of the camera body 3. As shown in FIG. 1B, an LCD display unit 6 and an EVF 7 are provided on the back of the camera body unit 3 to display a photographed image or reproduce and display a recorded image at the center.

  On the upper surface of the camera body 3, as shown in FIG. 2A, a shutter button 5 that captures a captured image and records it on the memory card 13, and a “recording mode” (REC in the figure) near the shutter button 5. ) And “playback mode” (PLAY in the figure) are provided. The recording mode is a mode for taking a picture, and the reproduction mode is a mode for reproducing and displaying a photographed image recorded on the memory card 13 on the LCD display unit 6 or the EVF 7.

  Further, as shown in FIG. 2A, a photographing sensitivity changeover switch 10 for switching photographing sensitivity is provided on the upper surface of the camera body 3. The photographing sensitivity changeover switch 10 can switch the photographing sensitivity cyclically from ISO100 to ISO800 each time the switch is pressed, for example, and select a sensitivity suitable for the situation at the time of photographing.

  As shown in FIG. 1B, a playback frame advance switch / zoom switch 9 is provided on the rear surface of the camera body 3 for performing frame advance of a playback image during playback and zooming during shooting. Yes. The frame advance of the playback image by the playback frame advance switch / zoom switch 9 is a mode in which the camera is set to the playback mode and the images recorded on the memory card 13 are sequentially displayed on the LCD display unit 6 together with the frame number. . Note that it is possible to instruct to change the image display on the LCD display unit 6 in the ascending order direction (direction of photographing order) or the descending order direction (direction opposite to the photographing order). The zoom operation at the time of shooting is to zoom the macro zoom lens 201 in the tele direction or the wide direction by operating the playback frame advance switch / zoom switch 9.

  Further, an EVF changeover switch 8 for selecting an LCD display unit 6 and an EVF 7 which are display means for displaying an image is provided on the back surface of the camera body unit 3.

  Next, the control system of the digital camera 1 will be described with reference to FIG. FIG. 3 is a block diagram of the control system of the digital camera 1. In FIG. 3, the same members as those shown in FIGS. 1 and 2 are given the same numbers.

  The macro zoom lens 201 in the imaging unit 2 is provided with a diaphragm member (fixed diaphragm) having a fixed aperture. A CCD area sensor 202 (hereinafter abbreviated as CCD 202) is a color area image pickup in which R (red), G (green), and B (blue) primary color transmission filters are arranged in a checkered pattern in pixel units (pixel units). This is a type in which all pixels are read out by a sensor, and a light image of a subject formed by the macro zoom lens 201 is received as an image signal of R (red), G (green), and B (blue) color components (received by each pixel). Signal that is a signal sequence of pixel signals that has been subjected to photoelectric conversion and output. That is, the CCD 202 functions as an imaging unit in the imaging apparatus according to the present invention.

  The exposure control in the imaging standby state in the imaging unit 2 is performed by adjusting the exposure amount of the CCD 202, that is, the charge accumulation time of the CCD 202 corresponding to the shutter speed, because the aperture is an open fixed aperture by the aperture driver 208. . To adjust the charge accumulation time, first, the exposure control data is calculated by the camera control CPU 311 based on the photometric area selected from the light quantity data photometrically measured by the CCD 202. Then, based on the calculated exposure control data and a preset program diagram, the timing generator 209 feeds back the exposure time for the CCD 202 to be appropriate, and exposure control is performed.

  If an appropriate shutter speed cannot be set when the subject brightness is low, an inappropriate exposure due to insufficient exposure is corrected by adjusting the level of the image signal output from the CCD 202. That is, when the brightness is low, exposure control is performed by combining the shutter speed and gain adjustment. The level adjustment of the image signal is performed in the gain adjustment of the AGC circuit 205 in the signal processing circuit 203 described later.

  At the time of shooting, the exposure amount to the CCD 202 is controlled by the aperture driver 208 and the timing generator 209 according to a preset program diagram based on the exposure control data.

  The timing generator 209 generates a drive control signal for the CCD 202 based on a reference clock transmitted from a reference clock generator 308 described later. The timing generator 209 generates, for example, a clock signal such as an integration start / end (exposure start / end) timing signal, a light reception signal readout control signal (horizontal synchronization signal, vertical synchronization signal, transfer signal, etc.) of each pixel, By outputting to the CCD 202, the driving of the CCD 202 is controlled.

  Further, the timing generator 209 can convert and supply the phase of the sampling signal used in the CDS circuit 204 in the signal processing circuit 203 described later based on the reference clock supplied from the reference clock generation unit 308. It is. As described above, the timing generator 209 functions as a drive control signal generation unit and a sampling signal phase control unit in the imaging apparatus according to the present invention.

  When the charge accumulation is completed, the photoelectrically converted signal is shifted to a light-shielded transfer path in the CCD 202, and is read out from this through a buffer.

  The signal processing circuit 203 performs predetermined analog signal processing on the image signal (analog signal) output from the CCD 202. The signal processing circuit 203 includes a CDS (correlated double sampling) circuit 204 and an AGC (auto gain control) circuit 205. The CDS circuit 204 reduces the noise of the image signal, and the gain adjustment of the AGC circuit 205 adjusts the image signal. Adjust the level. The AGC circuit 205 controls the photographing sensitivity by performing gain adjustment based on the photographing sensitivity selected by the photographing sensitivity changeover switch 10 described above. That is, the photographing sensitivity changeover switch 10 functions as photographing sensitivity selection means in the image pickup apparatus according to the present invention, and the AGC circuit 205 functions as photographing sensitivity control means in the image pickup apparatus according to the present invention.

  The A / D converter 206 converts each pixel signal of the image signal input from the imaging unit 2 into a 12-bit digital signal. The A / D converter 206 converts each pixel signal, which is an analog signal, into a 12-bit digital signal based on the A / D conversion clock input from the reference clock generation unit 308.

  The image signal digitized in this way is then taken into the image processing CPU 301 and subjected to predetermined processing. The image processing CPU 301 functions as image processing means in the imaging apparatus according to the present invention. The image processing CPU 301 is composed of a microcomputer, and controls the photographing operation of the digital camera 1 by organically controlling the driving of each member in the imaging unit 2 and the camera body unit 3 described above.

  Hereinafter, a predetermined process for an image signal performed by the image processing CPU 301 will be described.

  First, the image signal captured by the image processing CPU 301 is written in the image memory 313 as a storage unit in synchronization with the reading of the image signal output from the CCD 202. In the processing of the image signal performed by the image processing CPU 301, data written in the image memory 313 is accessed, and processing in each block is performed using the data recorded in the image memory 313.

  The pixel interpolation unit 302 performs average interpolation (also referred to as pixel interpolation) after masking the image data recorded in the image memory 313 with the filter pattern of each RGB pixel. Among these, G having pixels up to a high band is replaced with an average value of intermediate binary values of four surrounding pixels by a median (intermediate value) filter, and average interpolation is performed. Average interpolation.

  The resolution conversion unit 303 performs a reduction process in the horizontal direction and the vertical direction or a thinning process on the image signal subjected to the pixel interpolation in the pixel interpolation unit 302, and can handle the set number of recorded image pixels. It is to convert to. At the same time, the horizontal pixel thinning process is also performed on the monitor display image signal to convert it to a low resolution image signal that can be displayed on the LCD display unit 6 and the EVF 7.

  The white balance control unit 304 performs level conversion of R, G, and B color component image signals that have undergone resolution conversion processing. In the white balance processing, a part that is supposed to be white is estimated from the image data read from the image memory 313 at the time of shooting standby based on luminance, saturation data, etc., and the average value of each of R, G, and B, G / The R ratio and G / B ratio are obtained, and correction control is performed as R and B correction gains.

  In the present invention, the white balance control unit 304 can also detect color unevenness. Specifically, image data of a preset region is read from the image memory 313, and a predetermined calculation process is performed on the read image data to detect the amount of color unevenness. It functions as unevenness detection means.

  Here, a method for detecting color unevenness is described. FIG. 4 is a schematic diagram showing a region where color unevenness is detected.

  In an imaging apparatus having an imaging element with a high-density pixel of 1 million pixels or more, as described above, when the drive speed of the image signal is increased, the transfer characteristics vary among the pixels, and as a result, color unevenness occurs. May occur. Color unevenness can be confirmed from the occurrence of an area where the color varies from the left to the right on the screen (LCD display unit 6 or EVF 7). When detecting color unevenness, first, areas for detecting color unevenness are set. As shown in FIG. 4, the detection areas are arranged at the left end center portion and the right end center portion of the screen, respectively. Here, the reason why the detection area is arranged at the center with respect to the vertical direction of the screen is to reduce the measurement error due to the luminance unevenness as much as possible. The detection area provided at the center of the left end is C1, and the detection area provided at the center of the right end is C2.

  The amount of color unevenness is obtained by measuring the luminance and saturation of R, G, and B light in the detection region. Specifically, the R / G ratio and the B / G ratio in the detection area 1 and the detection area 2 are calculated by comparison.

Also, the R, G, and B light intensities obtained in the detection area are coordinate-converted into uniform color-difference color space coordinates (L ^* , a ^* , b ^* ), and the amount of color unevenness is calculated from the a ^* and b ^* colors. It is also possible to determine the amount of unevenness. That is, the R, G, B light intensities (R ₁ , G ₁ , B ₁ ) in the detection area 1 are (L ₁ ^* , a ₁ ^* , b ₁ ^* ), and the R, G, B light intensities in the detection area 2 (R ₂ , G ₂ , B ₂ ) is converted to (L ₂ ^* , a ₂ ^* , b ₂ ^* ), and a ₁ ^* , a ₂ ^* and b calculating the color unevenness quantity by comparison operation ₁ ^* and b ₂ ^*. In this way, the white balance control unit 304 can detect color unevenness.

  In the imaging apparatus according to the present invention, when the white balance control unit 304 serving as color unevenness detection means detects color unevenness, the image processing CPU 301 can control the reference clock generation unit 308 to perform color unevenness correction. .

  The reference clock generation unit 308 is a circuit that forms a reference clock used for driving control of the digital camera 1 and supplies the reference clock to each circuit. Specific examples of the reference clock in the present invention include a reference clock used for the timing generator 209, an A / D conversion clock used for the A / D converter 206, and the like. Generate a clock. Thus, the reference clock generation unit 308 functions as a reference signal generation unit in the imaging apparatus according to the present invention.

  Here, a method of correcting the color unevenness performed in the imaging apparatus according to the present invention will be described with reference to a schematic diagram of the drive signal frequency switching in FIG. FIG. 5A shows waveforms of the pixel clock based on the normal reference clock, the output signal of the CCD 202, and the sampling signal (base part; SHP, data part; SHD), and FIG. 5B shows the reference. The waveforms of a pixel clock, a CCD output signal, and a sampling signal that are generated when the clock is slowed down are shown.

  The present inventor has noted that the cause of color unevenness occurring in an image pickup apparatus using a high-pixel image pickup element exceeding 1 million pixels is due to the increase in the drive signal frequency of the CCD 202. That is, in FIG. 5A, when the frequency of the pixel clock becomes very high, the rising waveform and falling waveform of the pixel clock are lost. As a result, the ON / OFF time is shortened and the charge of the CCD 202 is transferred. The necessary potential (potential) cannot be obtained. As a result, color unevenness occurs.

  Therefore, the present inventor controls the formation of the reference clock formed by the reference clock generation unit 308 by the image processing CPU 301 when the occurrence of color unevenness is detected, and the pixel clock as shown in FIG. The inventors of the present invention have found the present invention as a result of studying that it is possible to suppress the occurrence of color unevenness by intentionally reducing the drive signal frequency (pixel clock) of the CCD 202 by reducing the frequency.

  Further, the present inventor also paid attention to the frequency of the sampling signal (SHP, SHD) in the CDS circuit 204 when the pixel clock of the CCD 202 is slowed down, and the sampling signal is automatically slowed down as the pixel clock is slowed down. However, we realized that the optimal timing for sampling is still in a very narrow range. Therefore, the present inventor has studied a method that can obtain an optimal timing for sampling with respect to a sampling signal whose frequency is reduced, and that the optimal timing for sampling can be obtained by changing the phase of the sampling signal. I found it. Then, it was found that the color unevenness can be corrected more effectively when the phase of the sampling signal is changed in this way, and the invention according to claim 3 has been reached.

  As described above, the present invention corrects the color unevenness caused by the variation in the transfer characteristic of the pixel signal generated in the image pickup apparatus using the image pickup device having a high pixel density, and transfers the CCD 202 by reducing the pixel clock. This is an invention that is achieved by improving the characteristics, and further, by varying the phase of the sampling signal that has been slowed down, to prevent the occurrence of color unevenness with higher accuracy.

  In the present invention, with the above configuration, the image sensor can sufficiently stabilize the potential potential after the charge is transferred and before the next charge is transferred, and each pixel signal is transferred after obtaining a sufficient potential potential. Thus, there is no variation in the transfer performance between pixel signals. Therefore, it was confirmed that uneven density due to variations in transfer characteristics between pixel signals was eliminated. Furthermore, if the operation of changing the phase of the sampling signal supplied to the CDS circuit 204 that has been slowed down as the frequency of the pixel clock formed by the timing generator 209 is slowed down, the problem of color unevenness is more reliably solved. I found out that

  Further, in the present invention, in addition to the above-described color unevenness correction method, it has also been found that color unevenness can be made inconspicuous by correcting the matrix coefficient used in the matrix calculation unit 306 in the image processing CPU 301.

  This color unevenness correction method is effective under photographing conditions with a certain degree of high sensitivity, such as when the photographing sensitivity is ISO 400 or higher. Hereinafter, this method will be described.

  The matrix calculation unit 306 converts an image signal represented by R, G, and B light that has been subjected to gamma correction processing by the gamma correction unit 305 of the image processing CPU 301 into a Y signal (luminance) using a coordinate conversion formula represented by the following Equation 1. Signal) and color difference signals (Cr (R−Y) signal and Cb (B−Y) signal), and values obtained by the conversion are stored in the image memory 313.

  The gamma correction unit 305 corrects the γ characteristic of the image signal and converts the image signal into, for example, an 8-bit image signal suitable for the characteristics of the output device.

  In the formula, a, b, c, d, e, f, g, h, and i are matrix coefficients for coordinate transformation.

  The matrix calculation unit 306 has a property of suppressing the reproduced color of the low-saturation image signal and functions as a so-called low-saturation color signal suppression unit.

  In the present invention, paying attention to the fact that the matrix calculation unit 306 has the property of suppressing the reproduced color of the low-saturation image signal, the color coefficient is adjusted by adjusting the matrix coefficient value described above according to the shooting situation. This is intended to correct unevenness.

  Specifically, when the values of the color difference signals (Cr and Cb) calculated by the coordinate conversion formula of Formula 1 are smaller than any preset value, the saturation of the captured image is low. In such a case, color unevenness can be reduced by correcting the color difference component by multiplying the matrix coefficients d, e, f, g, h, i by a correction coefficient value of 0 or more and less than 1. I found.

  Note that color unevenness is not noticeable in a chromatic color photographed image, so the color difference signal is corrected only when the color difference signal is smaller than a predetermined value.

  As described above, in the present invention, when photographing with high sensitivity, the matrix coefficient for the color difference signal of the matrix calculation unit 306 functioning as a low-saturation color signal suppressing unit in the imaging apparatus is corrected, thereby achieving high sensitivity. It was found that correction can be made so as to make the color unevenness generated under the shooting conditions inconspicuous.

  Further, the image processing CPU 301 includes an image compression unit 307 that generates a compressed image for image recording when a captured image is recorded. The image compression unit 307 generates compressed image data of a selected compression rate K by performing a predetermined compression process on a captured image by a JPEG (Joint Photographic Coding Experts Group) method such as two-dimensional DCT conversion and Huffman coding, The compressed image data is recorded on the memory card 13.

  Next, signal processing in the image processing CPU 301 under each state of the digital camera 1 will be described. In the photographing standby state, for example, image signals are taken into the image processing CPU 301 from the imaging unit 2 at predetermined intervals such as every 1/30 seconds. The captured image signal is subjected to predetermined signal processing from the pixel interpolation unit 302 to the matrix calculation unit 306, and the image signal subjected to the signal processing is recorded in the image memory 313.

  Then, the image signal recorded in the image memory 313 is read out, the read image signal is encoded into NTSC / PAL by the video encoder 309, and this is displayed on the LCD display unit 6 and the EVF 7 as a field image.

  At the time of image recording, after the compression processing is performed by the image compression unit 307 in order to obtain an image of the set recording resolution, the compressed image is recorded on the memory card 13 by the memory card driver 310.

  In the playback mode for playing back recorded images, the image signal read from the memory card 13 is subjected to predetermined signal processing by the image processing CPU 301 and then applied to the LCD display unit 6 and the EVF 7 via the video encoder 309. indicate.

  A switch group 312 in FIG. 3 corresponds to the shutter button 5, EVF change switch 8, playback frame advance switch / zoom switch 9, shooting sensitivity change switch 10, and shooting mode change switch 11 in FIGS. 1 and 2. Switch.

  Next, the adjustment process of the drive signal frequency control and sampling phase control of the digital camera 1 will be described with reference to the flowchart shown in FIG. In the adjustment step, adjustment is performed by imaging a white chart with uniform reflectance.

  First, the digital camera 1 is set to the adjustment mode (step S1). Here, the adjustment mode means that a personal computer storing an adjustment program is connected to the digital camera 1, and AE (Automatic Exposure adjustment), AWB (Auto White Balance), AF (automatic white balance adjustment), AF (automatic exposure adjustment) This is a mode for setting various parameters as a reference when controlling adjustment such as Auto focus (automatic focus adjustment). In the digital camera 1, a parameter for controlling the frequency of the control signal generated by the drive control signal generation unit and a parameter for controlling the phase of the sampling signal supplied to the CDS circuit are set at the stage of the adjustment mode.

  When the digital camera 1 is set to the adjustment mode, the camera enters a shooting standby state, and an image in the shooting standby state is displayed. (Step S2).

  Next, the gain of the AGC circuit 205 is set by selecting the photographing sensitivity. The photographing sensitivity is selected from four types of sensitivity, for example, ISO 100, 200, 400, and 800, by a photographing sensitivity changeover switch provided on the upper surface of the camera body 3. In the initial adjustment process, ISO 100 is set. (Step S3).

  Next, the white balance control unit 304 reads image data of a preset region from the image memory 313, performs a predetermined calculation based on the read image data, and detects the amount of color unevenness. (Step S4).

  When the amount of color unevenness is detected, it is determined whether or not the detected amount of color unevenness is greater than a preset reference value (step S5). If the amount of color unevenness is greater than or equal to the reference value (step S5). ; Yes), the image processing CPU 301 controls the driving of the reference clock generator 308 to change the frequency of the reference clock for the timing generator 209 in the low speed direction. (Step S6).

  Then, the reference clock generation unit 308 changes the phase of the sampling signal of the CDS circuit 204 based on the frequency of the reference clock changed in the low-speed direction in step S6 described above. (Step S7). By performing the processing of step S6 and step S7, the amount of color unevenness is reduced, and then the process returns to step S4 again, and these operations are repeated until the amount of uneven color becomes equal to or less than the reference value.

  When it is confirmed that the amount of color unevenness does not satisfy the reference value (step S5; No), it is confirmed whether or not the setting of the photographing sensitivity has been completed. (Step S8). If the photographing sensitivity setting has not been completed (step S8; No), the photographing sensitivity is set again (step S3), and the above operation is repeated. If it has been completed (step S8; Yes), the set photographing sensitivity value and the frequency of the reference clock changed in step S6 are stored in the memory (step S9), and further changed in step S7. The phase of the sampling signal of the CDS circuit 204 is stored in the memory. (Step S10).

  Thus, the adjustment process is completed, and at the time of shooting, based on the shooting sensitivity selected by the shooting sensitivity switch 10, the frequency of the reference clock stored in the memory and the phase of the sampling signal of the CDS circuit 204 are read out. The processing CPU 301 corrects the amount of color unevenness by controlling the frequency of the reference clock of the reference clock generation unit 308 and the phase of the sampling signal based on the read photographing sensitivity setting value and sampling phase setting value.

  Next, a method for correcting color unevenness performed under high-sensitivity shooting conditions so as to be inconspicuous will be described with reference to the flowchart of FIG.

  First, the digital camera 1 is set to a recording mode and is set in a shooting standby state. (Step S21). In the shooting standby state, a shooting standby image is displayed on the LCD display unit 6 of the digital camera 1. (Step S22).

  Next, the photographing sensitivity set by the photographing sensitivity changeover switch 10 is confirmed (step S23), and this value is stored in the memory. Here, the case where color unevenness correction is necessary is assumed to be a case where the photographing sensitivity is ISO 400 or higher. Then, it is determined whether or not the photographing sensitivity is ISO400 or higher. (Step S24). When the shooting sensitivity is set automatically, the automatically set shooting sensitivity is confirmed (step S23), and this value is stored in the memory.

  If the photographing sensitivity is less than ISO400 (step S24; Yes), it is determined that the color unevenness is not conspicuous and it is not necessary to perform correction to the matrix calculation unit 306, and matrix matrix conversion is performed as it is (step S25). The conversion of the R, G, and B signals into the luminance signal and the color difference signal is completed without performing it. (Step S28).

  On the other hand, when the photographing sensitivity is ISO400 or higher (step S24; No), it is determined that correction of color unevenness is necessary, and the matrix coefficient for color difference signal conversion in the conversion formula used in the matrix calculation unit 306 is corrected. The correction value k to be set is set in advance. (Step S26). The correction value k is a value in the range of 0 <k <1, and a correction value corresponding to the photographing sensitivity is set in advance.

  Next, matrix conversion is performed as in the case where the photographing sensitivity is less than ISO 400 (step S25), and it is determined whether or not the obtained color difference signals Cr and Cb are larger than the reference value. (Step S27). Here, when the value of the color difference signal is larger than the reference value, the conversion operation of the R, G, and B signals is completed without correcting color unevenness (step S28), but when the value is smaller than the reference value (step S27). No), the obtained color difference signals Cr and Cb are multiplied by the correction value k described above to correct the color difference signal. (Step S29). This will be described in detail below.

  In this operation, when the photographing sensitivity is high, correction is performed by multiplying the matrix coefficient for color difference signal conversion by the correction value k. In the present invention, when the shooting sensitivity is ISO 400 or higher, the sensitivity is high. However, when the shooting sensitivity is high, it is determined that the color unevenness is conspicuous, and the color difference signal conversion in the above-described coordinate conversion formula (Formula 1) is performed. A correction value k for correcting the matrix coefficient to be used is set in advance. Then, it is determined that the values of the color difference signals Cr and Cb obtained by the matrix conversion do not satisfy the reference value (No in step S27), and the matrix coefficients d, e, f, g, h, used for the color difference signal conversion are determined. Correction is performed by multiplying i by a correction coefficient k. In the present invention, the value of the correction coefficient k is set in advance, for example, set to 0.8 in the case of ISO400, and set to 0.5 in the case of ISO800. In this way, when performing low saturation color signal suppression control, the correction coefficient k to be applied to the matrix coefficient is set in consideration of the tendency that the color unevenness becomes more conspicuous as the imaging sensitivity increases.

  As described above, according to the present invention, when the photographing sensitivity is higher than the predetermined sensitivity, the matrix processing unit 306 corrects the matrix coefficient used for the color difference signal conversion so as to make the color unevenness inconspicuous. Is possible.

  As described above, according to the present invention, since the color unevenness caused by the transfer characteristics of the image sensor can be reduced according to the shooting conditions, high-quality can be achieved by correcting the color unevenness according to the shooting conditions. It has become possible to obtain captured images. In particular, the present invention is effective in correcting color unevenness caused by variations in transfer characteristics that have occurred due to high-speed pixel signal driving in an imaging device having a high pixel density exceeding 1 million pixels. As a result, it was possible to express high-quality image reproducibility.

  In the embodiment described above, the drive signal frequency control and sampling phase control operation of the digital camera 1 in the adjustment process has been described. However, the present invention stores the adjustment program in the digital camera 1 without using a personal computer, It is also possible to adopt a configuration that allows the photographer to make adjustments.

  The drive signal frequency control, sampling phase control, and low-saturation color signal suppression control are corrected using the shooting sensitivity as a parameter. However, the correction operation is switched according to the shooting scene. Good. For example, when shooting a fast-moving subject such as a sports scene, even if the shooting sensitivity is set to high sensitivity, the frame rate is maintained at high speed without driving at low speed by drive signal frequency control, and subject tracking is performed. Operates with emphasis on sex. On the other hand, when shooting subjects that require static and high-definition rendering performance such as landscapes and portraits, even if the shooting sensitivity is set to low sensitivity, drive signal frequency control, sampling phase control, In addition, it is possible to perform an operation that emphasizes high-quality image reproducibility by correcting color unevenness by low saturation color signal suppression control.

It is the front view and back view of the digital camera which concern on this invention. It is the top view and side view of the digital camera which concern on this invention. It is a block block diagram in the digital camera which concerns on this invention. It is a schematic diagram which shows the area | region which detects color unevenness. It is a schematic diagram of drive signal frequency switching. It is a flowchart of color unevenness correction by drive signal frequency control and sampling phase control. It is a flowchart of color unevenness correction by matrix coefficient correction for image signal conversion.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Digital camera 2 Imaging part 201 Macro zoom lens 202 CCD area sensor 203 Signal processing circuit 204 CDS circuit 205 AGC circuit 206 A / D converter 207 Focus motor driver 208 Aperture driver 209 Timing generator 3 Camera main body 301 Image processing CPU
302 Pixel Interpolation Unit 303 Resolution Conversion Unit 304 White Balance Control Unit 305 Gamma Correction Unit 306 Matrix Operation Unit 307 Image Compression Unit 308 Reference Clock Generation Unit 309 Video Encoder 310 Memory Card Driver 311 Camera Control CPU
312 Switch group 313 Image memory 4 Flash 5 Shutter button 6 LCD display 7 EVF
8 EVF switch 9 Playback frame advance switch / zoom switch 10 Shooting sensitivity switch 11 Shooting mode switch 12 External connection terminal 13 Memory card C1, C2 Color unevenness detection area

Claims (6)

Imaging means for photoelectrically converting a subject light image into an image signal and capturing the image;
Drive control signal generating means for generating a control signal for controlling driving of the imaging means;
Reference signal generating means for generating a reference signal used in the drive control signal generating means;
Image signal processing means for performing predetermined processing on the image signal;
Detecting means for detecting an output state of an image formed based on the image signal,
The image signal processing means includes
Based on the detection result of the detection means,
An image pickup apparatus that controls the operation of the reference signal generation means so that the frequency of the reference signal generated by the reference signal generation means varies. The imaging apparatus according to claim 1, wherein the image signal processing unit controls the operation of the reference signal generation unit so that the frequency of the reference signal is reduced. The imaging apparatus according to claim 1, wherein the detection unit detects color unevenness generated in the image signal. The imaging apparatus includes a CDS circuit that samples an image signal captured by the imaging unit,
The sampling signal used in the CDS circuit is generated and supplied by the drive control signal generating means,
The imaging apparatus according to claim 1, wherein the drive control signal generation unit supplies a sampling signal whose phase is changed based on a detection result of the detection unit to the CDS circuit. Conversion means for converting the image signal captured by the imaging means into a luminance signal and a color difference signal;
5. The image signal processing unit according to claim 1, wherein the image signal processing unit corrects a conversion condition used by the conversion unit based on a set photographing sensitivity to form a color difference signal. The imaging device described. The imaging device according to claim 1, wherein the detection by the detection unit is performed when the imaging device is adjusted.

Images