JP2007074363A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus capable of performing black level correction stably at digital zooming etc. for reading an image signal in a partial read-out mode to form a high-definition image. <P>SOLUTION: When an image signal is displayed or recorded in a mode for reading a photoelectric converted charge at some region on an imaging device to form an image signal, the imaging apparatus controls so as to read the photoelectric converted charge at a position in front of a predetermined region to form the image signal. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an imaging apparatus, and more particularly to an imaging apparatus that performs black level correction of an imaging element.

  In an imaging apparatus such as an electronic camera, a scanner, and a video camera, an image is formed by converting a subject optical image into an image signal by an imaging device typified by a CCD (Charge Coupled Device). In these imaging apparatuses, it is necessary to stabilize the black level that is the reference of the image signal. The black level has a great influence on image reproducibility and image quality, and therefore it is necessary to stabilize the operation by operations such as correction in order to realize high-quality image formation. Various techniques for efficiently correcting the black level have been studied in the field of imaging devices.

  Here, a black level correction method generally performed will be described.

  First, the configuration of the CCD and the driving method will be described.

  Various types of imaging devices are known. For example, the configuration of a vertical overflow drain type CCD will be described with reference to FIG. FIG. 5A is a schematic diagram illustrating a pixel configuration of the CCD 50. FIG. 5B is a schematic diagram showing a CCD output signal and a clamp signal of an arbitrary horizontal line that scans the light receiving region 52. Note that the actual CCD output signal is a signal waveform that is inverted up and down with respect to the signal waveform shown in FIG. 5B.

  As shown in FIG. 5A, the CCD 50 includes a light receiving area 52 that converts an optical image of a subject into an image signal and a light shielding area 53 that forms a black level detection image signal (hereinafter, the light shielding area 53 is referred to as an OB area). ; Also referred to as an optical black region), and the light shielding region 53 has a structure arranged around the light receiving region 52.

  In the CCD 50, photodiodes 51 corresponding to photoelectric conversion units are arranged in units of pixels in the light receiving region 52 and the OB region 53. As shown in FIG. 5A, the photodiode 51 is connected to a vertical shift register (vertical CCD) 54, and the vertical shift register 54 is further provided with a horizontal shift register (horizontal CCD) 55 provided below the CCD 50. Connect with.

  The photodiode 51 provided in the OB region 53 is optically completely shielded from light, and only a charge signal resulting from dark noise caused by heat is formed. In the present invention, a charge signal caused by dark noise is also called an image signal.

  Next, a method for driving the CCD 50 having such a configuration will be described. The charge signal generated by the photodiode 51 is read to the vertical shift register 54 by the charge read pulse φTG1 or φTG3 output from the timing generator that drives the CCD 50. The read charge signal is transferred in the vertical direction by vertical transfer pulses φV1 to φV4 output from the timing generator. The timing generator outputs horizontal transfer pulses φH1 and φH2 to the horizontal shift register 55 each time a charge signal for one horizontal line is supplied from each vertical shift register 54 to the horizontal shift register 55. In response to the horizontal transfer pulses φH1 and φH2, a charge signal corresponding to one horizontal line is transferred in the horizontal direction. The horizontally transferred charge signal is output to the outside through the output unit 57. In this manner, a charge signal corresponding to one screen generated by each photodiode 51 is output from the CCD 50. As shown in FIG. 5B, the image signal output from the CCD 50 becomes a CCD output signal composed of a dummy pixel signal, a front stage OB signal, an image signal, and a rear stage OB signal from the front edge.

  Here, a black level correction method that is normally performed on the image signal read from the CCD 50 in this manner will be described.

  The black level correction is usually generated with pixels constituting the OB area at the right end of the imaging surface of the CCD 50 shown in FIG. 5A (only two pixels are shown in the horizontal direction in the figure, but corresponding to several tens of pixels). The extracted OB signal is extracted, and the image signal is corrected according to the extracted OB signal level. Specifically, the subsequent stage OB signal is extracted from the CCD output signal based on the horizontal clamp signal shown in FIG. 5B, and the black level of the image signal is set as the reference potential based on the extracted OB signal level. Set the black level reference voltage. Based on the black level reference voltage set in this way, a clamp operation is performed in a CDS (correlated double sampling) circuit, whereby black level correction is performed.

  Normally, the black level is corrected in this way. Various techniques for efficiently correcting the black level have been studied in the field of imaging devices.

For example, an analog clamp unit and a digital clamp unit are provided as black level correction means, and the operation of the digital clamp unit is selected from two operation modes of field clamp and line clamp according to the CCD drive mode, and is driven in the still image mode. There is a technique that sometimes suppresses the occurrence of V sag (step) in the still image mode by selecting a line clamp operation (see, for example, Patent Document 1).
JP 2001-313864 A (see paragraph 0033 and the like)

  By the way, in recent years, as the multi-function and high performance of the image pickup apparatus have progressed, higher zoom performance has been required. In response to this need, various imaging devices that use a digital zoom in addition to the conventional optical zoom have been studied.

  However, in the partial readout mode, the image signal of a part of the imaging surface is read out, and in the digital zoom that electrically expands the readout image signal, the image signal of the unnecessary area is vertically transferred at high speed. I try to sweep it out. In this high-speed transfer period, since the clamping operation for black level correction is stopped, black level correction cannot be performed accurately, and a step called V sag may occur in the image signal. .

  Here, the black level correction operation during digital zoom will be described with reference to FIG. FIG. 3A shows an image signal readout area on the imaging surface in the digital game. FIG. 3B shows the vertical synchronization signal (VD). FIG. 3C shows a CCD output signal. FIG. 3D shows a clamp signal (CLP). FIG. 3E shows the clamp potential and the OB level.

  At the time of digital zoom, as shown in FIG. 3A, charges on the lower and upper imaging surfaces 71 and 81 of the CCD 50 are swept out, and only the charges on the central portion 61 are read out.

  As shown in FIG. 3C, the image signal read from the CCD 50 is not output during the sweep period ta1 of the screen lower portion 71 and the sweep period tb of the screen upper portion 81, but only during the read period tr of the screen center portion 61. Is output. Then, in the sweep period ta1 and the sweep period tb, the clamping operation is stopped as shown in FIG. Accordingly, the clamp potential in the sweep period ta1 and the sweep period tb in which the clamp operation is stopped is an unstable and fluttering potential as shown in FIG.

  In such a state, after the sweeping period ta1 ends, when the period moves to the reading period tr in which the clamping operation is performed, as shown in FIG. 3D, although the clamping operation is started, depending on the size of the time constant of the clamping circuit, It is difficult to instantaneously obtain a clamp potential corresponding to the OB level Vob shown in 3 (e). Originally, as indicated by a solid line in FIG. 3E, the clamp potential must reach the clamp potential corresponding to the OB level Vob instantly after the start of the clamp operation. However, depending on the time constant of the clamp circuit, Becomes difficult to follow and gradually changes as shown by the broken line to reach the required clamp potential. The potential difference between them is generated as a V sag (step) in the image signal, which is a factor that greatly impairs the image quality.

  As described above, in the digital zoom or the like for reading an image signal in the partial reading mode, a V sag is generated in the image signal and affects the image quality. Therefore, the influence is exerted by an appropriate black level correction operation or the like. Must be reduced.

  In the above-mentioned Patent Document 1, when the CCD is driven in the still image mode, the line clamp operation is performed to suppress the occurrence of V sag (step) in the still image mode. However, in digital zoom and the like that read out image signals in partial readout mode, it is difficult to obtain an appropriate clamp potential instantly even if line clamp operation is performed because the clamp operation has a long stop period. It is thought to become.

  The present invention has been made in view of the above problems, and in a digital zoom or the like that reads an image signal of a partial area of the imaging surface in the partial readout mode without causing an increase in price or complexity of the imaging device. An object of the present invention is to provide an imaging apparatus capable of stably correcting the black level and forming a high-quality image.

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

(1) an image sensor that photoelectrically converts a subject light image to generate an image signal;
Clamping means for clamping an image signal generated by the imaging device;
A drive control signal for controlling driving of the image sensor, and a drive signal generating means for generating a clamp signal used in the clamp means;
Drive signal control means for controlling the operation of the drive signal generation means;
An imaging apparatus having at least one of display means for displaying an image captured by the imaging element based on the image signal and recording means for recording the image,
The image sensor is driven in a partial read mode in which a charge photoelectrically converted in a part of a predetermined region on the image sensor is read and an image signal is generated, and the generated image signal is displayed on the display unit, or When recording on recording means,
The drive signal control unit is configured to read the charge photoelectrically converted in a region in front of the predetermined region and generate an image signal when performing reading in the vertical direction with the image sensor. An imaging device characterized by controlling operation.

  (2) The imaging device according to (1), wherein the imaging device is a CCD area sensor capable of high-speed vertical transfer operation.

  (3) The imaging device according to (1) or (2), wherein the predetermined area is located in a central portion of the imaging element in a vertical reading direction.

  (4) The imaging apparatus according to any one of (1) to (3), wherein a front area of the predetermined area is an area including at least five horizontal lines.

(5) The image sensor has a light shielding region,
The image pickup apparatus according to item (1), wherein the image signal generated in the light shielding region is clamped by the clamping means.

  In the inventions described in (1) and (2) of the means described above, in the partial readout mode, the photoelectrically converted charge is read out in a part of a predetermined area on the image sensor to generate an image signal, and the generated image signal When displaying or recording an image captured on the basis of the image sensor, photoelectric conversion is performed in an area located in front of the predetermined area with respect to the vertical reading direction of the image sensor in addition to the predetermined area to be displayed or recorded. The generated charge is also read out to generate an image signal, and the generated image signal is clamped.

  That is, for the problem that it is difficult to instantaneously obtain an appropriate clamp potential immediately after the start of the clamp operation, the clamp potential is read before reading the image signal generated in a predetermined area on the image sensor to be displayed or recorded. Was made stable. In other words, since the clamping operation can be started from the time point when the image signal generated in the area that does not need to consider the influence of the clamping mistake is read out, the clamp potential is set when the image signal generated in the predetermined area is read out. Stable and appropriate clamp potential can be obtained.

  As a result, it is possible to suppress the occurrence of V sag (step) that is difficult to remove in the partial readout mode, and it is possible to provide an imaging apparatus capable of forming a high-quality image. Particularly, it is suitable for a CCD area sensor capable of high-speed vertical transfer operation.

  In the invention described in (3) of the above means, the image signal is generated by reading out the photoelectrically converted charge in the region located in the central portion in the vertical reading direction of the image sensor in the partial reading mode. High-quality image formation is made possible by suppressing the occurrence of V-sag during digital zoom that expands the signal.

  According to the present invention described in (4) of the above means, when the image signal is read out in the partial read mode, before reading out the image signal generated in the predetermined area to be displayed or recorded, Since the read image signal is composed of at least 5 horizontal lines, the clamping operation can be stabilized during this period.

  According to the present invention described in (5) of the above means, the clamping means clamps the image signal generated in the light shielding region which becomes the reference of the image signal output from the image sensor. Therefore, the black level can be corrected with high accuracy.

  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 digital video camera, and the like are also included.

  The appearance of a digital camera that is one of the representative embodiments of the imaging apparatus according to the present invention will be described with reference to FIG. 1A is a side view of the digital camera 1 according to the present invention, and FIG. 1B is a rear view. As shown in FIG. 1A, the digital camera 1 is composed of a camera body 2 and a lens unit 3.

  The lens unit 3 includes a photographing lens having a macro zoom (not shown), a diaphragm, a shutter, and the like.

  The camera main body 2 includes an LCD monitor 211 formed of an LCD (Liquid Crystal Display), an EVF (Electronic View Finder) 210, and external connection terminals for connecting the digital camera 1 to a personal computer (not shown). The image signal captured by the CCD area sensor 241 described later is subjected to predetermined signal processing, image display on the LCD monitor 211 and EVF 210, and image recording on a recording medium such as a memory card 277 described later, Alternatively, processing such as image transfer to a personal computer is performed.

  As shown in FIG. 1A, a built-in flash 212 that is hopped up when necessary is provided on the upper surface of the camera body 2.

  Further, as shown in FIG. 1B, an LCD for displaying a photographed image, reproducing a recorded image, or displaying a GUI such as a menu screen or various statuses is displayed at a substantially central portion on the back of the camera body 2. A monitor 211 and an EVF 210 are provided. In other words, the LCD monitor 211 and the EVF 210 function as display means in the imaging apparatus according to the present invention.

  As shown in FIG. 1B, a shutter setting button 203 for setting the operation mode of the digital camera 1 is provided near the shutter button 201 on the upper surface of the camera body 2. . The operation mode of the digital camera 1 set by the mode setting dial 203 includes “still image mode”, “moving image mode”, “reproduction mode”, and the like.

  For example, the still image mode is a mode for taking a picture from the standby state to the shooting through the exposure control process, and the reproduction mode is a reproduction display of the shot image recorded on the memory card 277 on the LCD monitor 211 or the EVF 210. It is a mode to do.

  Further, as shown in FIG. 1B, a digital switch button 209 for changing the zoom magnification of the digital zoom is provided near the main switch 202, as shown in FIG. ing.

  Further, as shown in FIG. 1B, a menu button 207 for displaying a menu on the LCD monitor 211 and an image on the LCD monitor 211 near the menu button 207 are displayed at the lower back of the camera body 2. Is provided with a quick view button 208.

  Further, a selection / determination button 206 for performing various settings is provided at a substantially central portion on the back surface of the camera body 2. The selection / determination button 206 includes a jog dial (cross key) 204 for selecting various settings and a determination button 205 for confirming the setting selected by the jog dial (cross key) 204.

  Next, the control system of the digital camera 1 will be described with reference to FIG. FIG. 2 is a block diagram of a control system of the digital camera 1 according to the present invention. In FIG. 2, the same members as those shown in FIG.

  The CCD area sensor 241 (hereinafter abbreviated as CCD 241) corresponds to the image sensor in the present invention, and each color transmission filter for R (red) light, G (green) light, and B (blue) light is set in pixel units (pixels). A color area imaging sensor arranged in a checkered pattern in unit), and subject light image formed by the lens unit 3 is photoelectrically converted to R (red) light, G (green) light, and B (blue) light. Image signals (signals composed of a signal sequence of pixel signals received in units of pixels) are generated.

  In the CCD 241, as shown in FIG. 5A, photodiodes 51 are arranged in units of pixels in each of the light receiving region 52 and the OB region 53. As shown in FIG. 5A, the photodiode 51 is connected to a vertical shift register 54, and the vertical shift register 54 is connected to a horizontal shift register 55 provided below the CCD 241 and stored in the photodiode 51. The charged signal is amplified by the output unit 57 and output to the outside through these parts.

  The image signal readout operation performed by the CCD 241 includes, for example, “live view readout mode”, “still image readout mode”, “partial readout mode”, and the like.

  The live view readout mode is a mode in which image signals are output from the CCD 241 while performing pixel thinning at regular intervals, and finally displayed on the LCD monitor 211 and the EVF 210 in order to determine the angle of view in photographing. The still image reading mode is a mode in which there is a charge discharging period due to high-speed transfer of the vertical shift register 54 when the CCD 241 is driven, and is a mode normally used when shooting a still image. The partial readout mode is a mode in which charges converted photoelectrically in a part of a predetermined area of the CCD 241 are read to generate an image signal, and charges in an unnecessary area are swept out at a high speed. In this mode, a digital zoom process or the like is performed, and finally, display on the LCD monitor 211 or EVF 210 or recording on the memory card 277 is performed. A read signal necessary for each read operation mode is generated by a timing generator 248 described later.

  The timing generator 248 generates a drive control signal for the CCD 241 based on a reference clock transmitted from a reference clock generator 271 described later. The drive control signal generated by the timing generator 248 includes, for example, an integration start / end timing signal for controlling the exposure start and end timings in the CCD 241, and a light reception signal read control signal (horizontal synchronization signal, vertical synchronization). Clock signals such as signals, transfer signals, and the like. When these clock signals are supplied to the CCD 241, the CCD 241 performs drive control corresponding to each clock signal.

  The timing generator 248 generates a clamp signal used in a CDS circuit 243 and a switch circuit 246 in a signal processing circuit 242 described later based on a reference clock transmitted from a reference clock generation unit 271 described later.

  The form of the drive control signal and clamp signal generated by the timing generator 248 is controlled by a camera control CPU 291 described later in accordance with the image signal reading operation mode described above. That is, the timing generator 248 functions as drive signal generation means in the imaging apparatus according to the present invention.

  Next, the signal processing circuit 242 includes a CDS circuit 243, an AGC circuit 244, an A / D converter 245, a switch circuit 246, and a black level reference voltage setting unit 247. Is performed. Hereinafter, a predetermined process for the image signal performed by the signal processing circuit 242 will be described.

  A CDS (correlated double sampling) circuit 243 reduces noise generated at the time of reading from an image signal read from the CCD 241, or performs OB clamping based on the black level reference voltage generated by the black level reference voltage setting unit 247. The operation is performed to correct the black level.

  An AGC (automatic gain control) circuit 244 adjusts the gain of the image signal processed by the CDS circuit 243.

  The A / D converter 245 converts each pixel signal constituting the image signal input from the AGC circuit 244 into a digital signal. The A / D converter 245 converts each pixel signal of an analog signal into, for example, a 14-bit digital signal based on the A / D conversion clock input from the reference clock generation unit 271.

  Based on the clamp signal sent from the timing generator 248, the switch circuit 246 extracts the image signal in the OB area or the dummy pixel signal included in the image signal from the image signal output from the AGC circuit 244.

  The black level reference voltage setting unit 247 generates a black level reference voltage used when black level correction is performed in the CDS circuit 243 based on the image signal extracted by the switch circuit 246 or the dummy pixel signal. It is. That is, the timing generator 248, the CDS circuit 243, the switch circuit 246, and the black level reference voltage setting unit 247 function as clamping means in the imaging apparatus according to the present invention.

  In such a configuration, when the CCD 241 is driven in the partial reading mode, the present invention corrects the black level by using the optimum reading method and the clamping method, thereby making it difficult to remove the V sag. The image signal reading operation and clamping operation performed by the digital camera 1 are controlled so as to suppress the occurrence of (step). Details of the image signal readout operation and the clamp operation control will be described later.

  In this manner, the image signal read by the CCD 241 is subjected to predetermined processing by the signal processing circuit 242 and converted into a digital image signal. The digitized image signal is captured by the image processing CPU 261 and subjected to predetermined processing.

  The image processing CPU 261 is composed of a microcomputer, and comprehensively controls image signal processing operations performed by the digital camera 1. In the following, processing for a digital image signal performed by the image processing CPU 261 will be described.

  First, the image signal captured by the image processing CPU 261 is written into the image memory 275 in synchronization with the reading of the image signal output from the CCD 241. That is, the digital image signal used for the processing performed by the image processing CPU 261 is once recorded in the image memory 275, taken out from the image memory 275, and used for processing in each block.

  As shown in FIG. 2, the image processing CPU 261 includes, for example, a black level correction unit 263, a pixel interpolation unit 264, a digital zoom control unit 265, a white balance control unit 266, a gamma correction unit 267, a matrix calculation unit 268, a shading correction unit 269, The image processing unit 262 includes an image compression unit 270 and the like, and a reference clock generation unit 271, and the image processing unit 262 performs known image signal processing on the digital image signal extracted from the image memory 275. Then, the digital image signal that has been subjected to the predetermined processing in these parts is stored in the image memory 275 again.

  Here, the digital zoom control unit 265 enlarges the image signal read from the CCD 241 according to the digital zoom magnification set by the digital zoom button 209 in the partial read mode, and generates an image signal of one image. It is.

  The reference clock generation unit 271 is a circuit that generates 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 248, an A / D conversion clock used for the A / D converter 245, and the like. Generate a clock.

  Next, the LCD monitor 211 performs display of an image signal captured by the CCD 241 and GUI display.

  The LCD drive circuit 279 includes a buffer memory (VRAM) that temporarily stores an image signal read from the image memory 275 by the image processing CPU 261, and displays the image signal on the LCD monitor 211 as a field image.

  Next, the camera control CPU 291 is composed of a microcomputer, and controls the drive of each member of the camera body 2 and the lens unit 3 sequentially based on switch signals generated by switch operations of a switch group 295 to be described later. The overall shooting operation of 1 is controlled.

  Further, the camera control CPU 291 controls the operation of the timing generator 248 in accordance with the image signal readout operation mode set by the mode setting dial 203 or the digital zoom button 209 to perform the image signal readout operation and the clamp operation. Control. That is, the camera control CPU 291 functions as a drive signal control unit in the imaging apparatus according to the present invention. Details of the image signal readout operation and the clamp operation control will be described later.

  As described above, in the digital camera 1, the image processing CPU 261 performs the signal processing as described above on the image signal captured from the CCD 241, and records the image signal subjected to these processing in the image memory 275. .

  The digital camera 1 according to the present invention records the image signal captured from the CCD 241 under the mode set by the mode setting dial 203 in the image memory 275 or displays it on the LCD monitor 211 or EVF 210.

  In a shooting standby state (for example, a state in which the mode setting dial 203 is set to “still image mode”), image signals are taken in from the CCD 241 through the signal processing circuit 242 and image processing CPU 261 at predetermined intervals such as every 1/30 seconds. ing. As described above, the captured image signal is subjected to predetermined signal processing at a portion from the black level correction unit 263 to the shading correction unit 269 of the image processing unit 262 in the image processing CPU 261, and then as a digital image signal. It is recorded in the image memory 275. Then, the image signal recorded in the image memory 275 is read out, and the read image signal is displayed on the LCD monitor 211 or EVF 210 as a field image via the LCD drive circuit 279 or EVF drive circuit 280.

  Further, at the time of image recording, the image signal is compressed by the image compression unit 270 of the image processing unit 262 in the image processing CPU 261 to obtain an image of the set recording resolution, and the obtained compressed image is a memory card driver 276. To the memory card 277. That is, the memory card 277 functions as a recording unit in the imaging apparatus according to the present invention.

In the reproduction mode (the state in which “reproduction mode” is set by the mode setting dial 203), the image signal read from the memory card 277 is subjected to predetermined signal processing by the image processing CPU 261, and is driven by the LCD drive circuit 279 or EVF drive. 2 is displayed on the LCD monitor 211 and the EVF 210 via the circuit 286. The switch group 295 in FIG. 2 includes the shutter button 201, the main switch 202, the mode setting dial 203, the selection / decision button 206, the menu button 207, Switches corresponding to the quick view button 208, the digital zoom button 209, and the like.

  Here, an image signal reading operation and a clamping operation performed when the digital zoom operation for reading an image signal in the partial reading mode will be described.

  In the conventional image signal readout operation and clamp operation in the partial readout mode, as described above, as shown in FIG. 3A, the sweep period ta1 of the screen lower portion 71 and the screen upper portion 81 are set. The clamp operation is stopped during the sweep-out period tb. Then, after the sweeping period ta1 of the screen lower portion 71 ends, when the image signal readout period tr of the screen center portion 61 starts, the clamping operation starts as shown in FIG. 3D, but the OB shown in FIG. It is difficult to instantaneously obtain a clamp potential corresponding to the level Vob because of the time constant of the clamp circuit. Originally, as shown by the solid line in FIG. 3E, the clamp potential must reach the clamp potential corresponding to the OB level Vob instantly when the clamp operation is started, but it follows according to the size of the time constant of the clamp circuit. Cannot be achieved, and gradually changes as shown by the broken line to reach the originally required clamp potential. The potential difference between them occurs as a V sag (step) in the image signal, and the image quality is greatly impaired.

  In the present invention, when the CCD 241 is driven in the partial reading mode, the black level is corrected by using the optimum reading method and the clamping method, thereby generating the V sag (step) that has been difficult to remove in the past. The image signal reading operation and clamping operation performed by the digital camera 1 are controlled so as to be suppressed.

  Here, in the digital camera 1 according to the present invention, an image signal reading operation and a clamping operation performed during a digital zoom operation for reading an image signal in the partial reading mode will be described with reference to FIG. FIG. 4A shows an image signal readout area on the imaging surface during digital zoom. FIG. 4B shows the vertical synchronization signal (VD). FIG. 4C shows a CCD output signal. FIG. 4D shows the clamp signal (CLP). FIG. 4E shows the clamp potential and the OB level.

  Conventionally, as described above, after the sweeping period ta1 of the lower portion 71 of the screen ends, the electric charge photoelectrically converted in the predetermined area to be displayed or recorded, that is, the screen center portion 61 shown in FIG. As shown in FIG. 3 (d), the clamp operation has started from the time when it has shifted to the reading period tr. However, in the digital camera 1 according to the present invention, a predetermined display or recording target is provided. In addition to the area, that is, the screen center portion 61 shown in FIG. 4A, the electric charge photoelectrically converted in the area 62 located in front of the predetermined area is also read to generate an image signal. Then, as shown in FIG. 4D, the clamping operation is started from the time when the image signal readout period trx is shifted.

  That is, as described above, immediately after the start of the clamp operation, it is difficult to instantaneously obtain an appropriate clamp potential due to the size of the time constant of the clamp circuit. Therefore, in order to stabilize the clamp potential before shifting to the period tr for reading the image signal generated at the screen center 61 (predetermined area) to be displayed or recorded, the influence of the clamping error is taken into consideration. The clamp operation is started from the time when the image signal generated in the region 62 that does not need to be read is shifted to the read period trx. Note that the region 62 includes at least 5 horizontal lines in order to stabilize the clamp potential during the period trx.

  Accordingly, at the time when the period tr when the image signal generated in the screen center portion 61 (predetermined region) is read out, the clamp potential follows the OB level Vob so that an appropriate clamp potential can be obtained. As a result, it is possible to suppress the occurrence of V sag (step) that was difficult to remove.

  As described above, in the image pickup apparatus according to the present invention, when the image pickup element is driven in the partial read mode, it is difficult to remove conventionally by correcting dark noise using the optimum read method and clamp method. Further, the occurrence of V sag (step) can be suppressed, and an imaging apparatus capable of forming a high-quality image can be provided.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be changed or improved as appropriate. For example, in the above-described embodiment, the CCD area sensor is used as the image sensor, but a CMOS area sensor may be used.

1 is a schematic external view of a digital camera according to the present invention. It is a circuit block block diagram in the digital camera which concerns on this invention. It is a timing chart which shows clamp operation at the time of partial reading in the conventional imaging device. 6 is a timing chart showing a clamping operation at the time of partial reading in the digital camera according to the present invention. It is a schematic diagram which shows the example of the correction method of the general dark noise.

Explanation of symbols

1 Digital Camera 2 Camera Body 201 Shutter Button 202 Main Switch 203 Mode Setting Dial 204 Jog Dial (Cross Key)
205 OK button 206 Select / OK button 207 Menu button 208 Quick view button 209 Digital zoom button 210 Electronic viewfinder (EVF)
211 LCD monitor 212 Built-in flash 241 CCD area sensor 242 Signal processing circuit 243 CDS circuit 244 AGC circuit 245 A / D converter 246 Switch circuit 247 Black level reference voltage setting unit 248 Timing generator 251 Aperture / shutter drive circuit 252 Focus / zoom motor Drive circuit 261 Image processing CPU
262 Image processing unit 263 Black level correction unit 264 Pixel complementing unit 265 Digital zoom control unit 266 White balance control unit 267 Gamma correction unit 268 Matrix calculation unit 269 Shading correction unit 270 Image compression unit 271 Reference clock generation unit 275 Image memory 276 Memory card driver 277 Memory card 278 External communication I / F
279 LCD drive circuit 280 EVF drive circuit 291 Camera control CPU
292 Flash control circuit 295 Switch group (shutter button, etc.)
3 Lens unit 351 Focus / zoom motor 352 Aperture 50 CCD
51 Photodiode 52 Light-receiving area 53 Light-shielding area 54 Vertical shift register (vertical CCD)
55 Horizontal shift register (horizontal CCD)
56 Dummy pixel 57 Output section

Claims (5)

An image sensor that photoelectrically converts a subject light image to generate an image signal;
Clamping means for clamping an image signal generated by the imaging device;
A drive control signal for controlling driving of the image sensor, and a drive signal generating means for generating a clamp signal used in the clamp means;
Drive signal control means for controlling the operation of the drive signal generation means;
An imaging apparatus having at least one of display means for displaying an image captured by the imaging element based on the image signal and recording means for recording the image,
The image sensor is driven in a partial read mode in which a charge photoelectrically converted in a part of a predetermined region on the image sensor is read and an image signal is generated, and the generated image signal is displayed on the display unit, or When recording on recording means,
The drive signal control unit is configured to read the charge photoelectrically converted in a region in front of the predetermined region and generate an image signal when performing reading in the vertical direction with the image sensor. An imaging device characterized by controlling operation. The imaging device according to claim 1, wherein the imaging device is a CCD area sensor capable of high-speed vertical transfer operation. The imaging apparatus according to claim 1, wherein the predetermined area is located in a central portion of the imaging element in a vertical readout direction. The imaging apparatus according to claim 1, wherein a front area of the predetermined area is an area including at least five horizontal lines. The image sensor has a light shielding region,
The imaging apparatus according to claim 1, wherein the image signal generated in the light-shielding region is clamped by the clamping unit.

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