JP2006261929A - Image pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable an image pickup device, which has a CCD color area sensor, to display a color image while maintaining a stable AF performance even when the luminance (illuminance) of an object is degraded. <P>SOLUTION: When the luminance (illuminance) of an object is low, a CCD color area sensor switches a live view reading mode and an addition reading mode for each frame, and performs the reading operation of an image signal. A display part performs image display based on a live view image signal read in the live view reading mode period, and an AF control part performs AF control based on an addition luminance image signal read in the addition reading mode period for performing a stable AF operation. Even when the luminance(illuminance) of the object is deteriorated, the display part displays an image based on the color image signal for obtaining the color information of the object. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an imaging apparatus capable of displaying a color image while maintaining stable autofocus (AF) performance even when the luminance (illuminance) of a subject is lowered.

  In recent years, in an imaging device such as an electronic camera or a digital video camera, as the performance of an imaging device represented by a charge coupled device (CCD) has been improved, the speed of autofocus (hereinafter abbreviated as AF) has been increased. And stability has been demanded.

  On the other hand, when AF control is performed by a contrast method that detects the contrast of an image based on an image signal read from the image sensor and obtains an in-focus position, the sensitivity of the image sensor is reduced due to the smaller size and higher pixels. When the brightness (illuminance) of the subject decreases, the sensitivity is insufficient in the normal operation state of the image sensor, and the signal level necessary for AF control cannot be obtained. This is difficult to do and greatly affects AF performance.

  As described above, the high pixel density and high density of the image sensor are accelerating, but on the other hand, the signal level of the image signal is lowered due to the decrease in sensitivity, greatly affecting the AF performance in the low luminance region (low illumination region). ing. Therefore, the influence must be reduced by the operation of measures to increase sensitivity. In the field of image pickup devices, various techniques for efficiently reading out image signals have been studied so far in order to increase the signal level of image signals read out from the image pickup device.

  Here, a general CCD configuration and an image signal reading method will be described.

  First, various types of imaging devices are known. For example, the configuration of an interline CCD color area sensor capable of reading out five fields will be described with reference to FIG. FIG. 6 is a schematic diagram showing a pixel configuration of an interline CCD color area sensor (CCD) 60.

  The CCD 60 includes a light receiving region 62 in which photodiodes 61 corresponding to photoelectric conversion elements that are two-dimensionally arranged in a horizontal direction and a vertical direction and convert an optical image of a subject into an image signal are arranged in units of pixels, A vertical transfer unit (vertical shift register) 63 that sequentially transfers the charge accumulated in the diode 61 via a transfer gate (not shown) and then sequentially transfers the charge in the vertical direction, and sequentially transfers the charge transferred from the vertical shift register 63 in the horizontal direction. A horizontal transfer unit (horizontal shift register) 64 that outputs the output signal of the horizontal register 64 after amplification.

  In the CCD 60 configured as described above, the charges generated by the photodiode 61 are transferred gate pulses (charge reading pulses) φTG1, φTG3, φTG5, φTG7, φTG9 output from a timing generator (not shown) that drives the CCD 60. Is read into the vertical shift register 63. The read charges are transferred in the vertical direction by vertical transfer pulses φV1, φV3, φV5, φV7, and φV9 output from the timing generator.

  In addition, the timing generator outputs horizontal transfer pulses φH1 to φH2 each time the charge for one horizontal line is applied from each vertical shift register 63 to the horizontal shift register 64. In response to the horizontal transfer pulses φH1 to φH2, charges corresponding to one horizontal line are transferred in the horizontal direction. The horizontally transferred charge is output to the outside through the output unit 66. In this way, in the frame readout mode, all charges corresponding to one screen generated by each photodiode 61 are divided into five fields and output from the CCD 60. The frame readout mode is a mode that is used, for example, when high-resolution image capture is performed during actual photographing.

  Next, a mode for reading an image signal used for general AF control will be described with reference to FIGS. 6 and 7.

  As a mode for reading an image signal used for AF control, for example, there are operation modes such as a live view readout mode and an AF readout mode.

  First, the operation in the live view readout mode will be described. The live view readout mode is a readout mode in which processing speed is more important than vertical resolution, and is a mode for reading out an image signal for viewing a shooting standby image on a display device such as EVF (Electronic ViewFinder). The image signal read in the read mode may be used for AF control.

  Image signal readout in the live view readout mode is performed by, for example, reading predetermined four pixels 61A out of 20 pixels in the vertical direction of the photodiode 61 to the vertical shift register 63 and further performing vertical shift, as shown in part A in FIG. By adding and reading out two pixels of the same color in the register 63, a low-resolution live view image signal is read out at high speed. That is, in this mode, the readout speed is increased by reading out the charge corresponding to one screen generated by the photodiode 61 as a low-resolution image signal by thinning it out in the vertical direction.

  Next, the operation in the AF readout mode will be described. The AF readout mode is a mode for reading out image signals used only for AF control, and is a readout mode in which processing speed is more important than the live view readout mode. As shown in FIG. 7, in the readout operation of the live view readout mode, the readout of the image signal in the AF readout mode sweeps out the charges on the imaging surface upper part 62A and the lower part 62C of the CCD 60 at a high speed. High-speed reading is enabled by reading only the charge. That is, by reading only a few lines of the imaging surface central portion 62B from the image signal read in the live view read mode, the read speed is further increased compared to the live view read mode.

  As described above, the mode for reading the image signal used for the normal AF control includes an operation mode such as a live view readout mode and an AF readout mode. Further, the normal AF control operation is executed by operating the shutter button, and includes two operation steps. The first step is a step of performing coarse adjustment of the focus adjustment based on the live view image signal read in the live view read mode, which is executed by “half-pressing” the shutter button. The second step is performed by changing the shutter button from “half-pressing” to “full-pressing” and performing fine adjustment of the focus adjustment, and reading set according to the luminance (illuminance) of the subject. Fine adjustment of the focus adjustment is performed based on the image signal read out under the mode. That is, generally, when the subject brightness (illuminance) is high, the AF read mode is set, and when the subject brightness (illuminance) decreases, the image signal is read by switching to the live view read mode. This is because in the AF readout mode, readout is performed at a high frame rate to speed up AF control. On the other hand, if the subject brightness (illuminance) decreases due to the high frame rate, appropriate exposure is performed. Time cannot be secured, and the signal level of the read image signal decreases, making it difficult to perform a stable AF operation. For this reason, the frame rate is lower than that in the AF readout mode, and the live view readout mode is switched to ensure a long exposure time.

However, when the luminance (illuminance) of the subject is further reduced, the signal level necessary for AF control cannot be obtained even in the image signal read out in the live view readout mode. In this case, it is difficult to perform a stable AF operation, which may greatly affect AF performance. Therefore, the influence must be reduced by the operation of measures to increase sensitivity. In the field of imaging devices, various techniques for efficiently reading out an image signal have been studied so far in order to increase the signal level of the image signal read from the image sensor when the luminance (illuminance) of the subject decreases. It was. For example, a well-known technique for increasing the signal level of an image signal to be read by further reducing the frame rate in the live view readout mode and extending the exposure time, or the CCD monochrome disclosed in Patent Document 1 In a photometric apparatus having an area sensor, there is a technique in which a technique for increasing the signal level of an image signal read by horizontal pixel addition is applied to an imaging apparatus having a CCD color area sensor.
Japanese Patent Laid-Open No. 5-118913 (see paragraph 0008)

  In this way, with the improvement in performance of imaging devices, the increase in the number of pixels and the density of imaging devices is accelerating. This greatly affects the AF performance. Therefore, the influence must be reduced by the operation of measures to increase sensitivity.

  As a countermeasure to increase sensitivity, in the known method of reading out by reducing the frame rate in the above-mentioned live view readout mode, the exposure time can be extended by reducing the frame rate, and the read image signal The signal level is increased.

  However, when the frame rate is reduced, the AF control speed is lowered, and the AF performance is greatly affected. Furthermore, when shooting a subject that moves rapidly, such as a sports scene, if the frame rate is slow, the display image cannot follow the movement of the subject, making it difficult to determine the composition and missing the photo opportunity.

  Further, in the readout method in which the horizontal pixel addition technique in the CCD monochrome area sensor disclosed in Patent Document 1 is applied to the CCD color area sensor, a large signal output can be obtained even with the same amount of light as compared with the conventional readout method. Therefore, stable AF operation can be performed. However, in order to perform pixel addition without distinguishing colors, the read image signal lacks color signal information and becomes a monochrome image signal. That is, despite the use of a color image sensor, the display image displayed on the display device is a black and white image, and color information of the subject cannot be obtained.

  The present invention has been made in view of the above problems, and in an imaging apparatus having a CCD color area sensor, even when the luminance (illuminance) of a subject is reduced without causing the apparatus to be complicated or expensive, An object of the present invention is to provide an imaging apparatus capable of displaying a color image while maintaining stable AF performance.

  The above object can be achieved by the inventions described in claims 1 to 8 below.

(Claim 1)
A CCD color area sensor that photoelectrically converts a subject light image with a plurality of photoelectric conversion elements arranged two-dimensionally to generate an image signal, and an image is displayed based on the image signal generated by the CCD color area sensor An image pickup apparatus comprising: a display unit; an autofocus control unit that performs autofocus control based on an image signal generated by the CCD color area sensor; and a detection unit that detects luminance of a subject.
When the luminance of the subject detected by the detection means is low,
The CCD color area sensor reads out charges from a plurality of photoelectric conversion elements arranged in the vertical direction for each predetermined number of photoelectric conversion elements, generates a live view image signal, and displays the live view image signal on the display unit. A first frame for displaying an image based on a view image signal;
The CCD color area sensor adds and reads out the charges generated by a plurality of continuous photoelectric conversion elements arranged in the vertical direction or a plurality of continuous photoelectric conversion elements arranged in the horizontal direction, and adds them. An image pickup apparatus comprising: a CCD color area sensor control unit that generates a luminance image signal and executes a second frame for causing the autofocus control unit to perform autofocus control based on the added luminance image signal .

(Claim 2)
The image pickup apparatus according to claim 1, wherein the CCD color area sensor control unit alternately executes the first frame and the second frame.

(Claim 3)
The frame rate of the added luminance image signal read out in the second frame is higher than the frame rate of the live view image signal read out in the first frame. The imaging device described in 1.

(Claim 4)
The CCD color area sensor has an interline element structure capable of multi-field readout of 3 fields or more,
A vertical transfer unit that sequentially transfers charges accumulated in a plurality of continuous photoelectric conversion elements arranged in the vertical direction in the vertical direction;
A plurality of continuous photoelectric conversion elements arranged in the vertical direction are used as a unit pixel group, and provided between the first unit pixel group and a second unit pixel group adjacent to the first unit pixel group. , Forbidden pixels that prohibit the reading of charges to the vertical transfer unit,
2. The CCD color area sensor control means transfers a plurality of electric charges generated in the unit pixel group to the vertical transfer unit at the same time, performs addition, and generates the added luminance image signal. The imaging device described in 1.

(Claim 5)
The imaging apparatus according to claim 4, wherein vertical transfer pulses having the same phase are applied to a plurality of electrodes that are continuous in a vertical direction of the vertical transfer unit.

(Claim 6)
The CCD color area sensor adds a plurality of horizontal charges transferred to a horizontal transfer unit in the horizontal transfer unit or output unit to generate the added luminance image signal. The imaging apparatus according to 1.

(Claim 7)
In the CCD color area sensor, the amount of charge generated in a pixel provided with a red transmission filter is R, the amount of charge generated in a pixel provided with a green transmission filter is G, and a pixel provided with a blue transmission filter is used. The following relationship is satisfied, where B is the generated charge amount, Ya is the added luminance image signal, and n is an arbitrary positive integer: 7. The imaging device described in 1.
Ya = n × (R + 2 × G + B)
(Claim 8)
Storage means for temporarily storing the live view image signal and the added luminance image signal read by the CCD color area sensor;
The live luminance image signal composed of the luminance signal and color signal temporarily stored in the storage means and the additional luminance image signal composed of the additional luminance signal are read out, and the additional luminance signal is included in the luminance signal constituting the live view image signal. Image synthesis means for adding or replacing the luminance signal constituting the live view image signal and the added luminance signal;
The imaging apparatus according to claim 1, wherein the imaging apparatus includes:

  According to the first and second aspects of the present invention, when the detection result of the detecting means for detecting the luminance (illuminance) of the subject is low luminance, the CCD color area sensor performs the live view reading mode and the addition reading. The mode is alternately switched for each frame and the image signal is read out. The display unit displays an image based on the live view image signal read out in the live view readout mode, and the AF control unit performs addition reading. AF control can be performed based on the added luminance image signal read in the mode. That is, when the luminance (illuminance) of the subject is reduced, a stable AF operation is performed by performing AF control based on the added luminance image signal that can obtain a large output even with the same light amount as compared with the normal reading operation. To be able to Even when the luminance (illuminance) of the subject decreases, the display unit can obtain color information of the subject by displaying an image based on the live view image signal.

  According to the third aspect of the present invention, the frame rate of the additional luminance image signal is increased, and the readout time of the additional luminance image signal is shortened. It is possible to suppress a decrease in the frame rate of the live view image signal caused by performing an image signal read operation by alternately switching each time.

  According to the fourth aspect of the present invention, the CCD color area sensor transfers a plurality of charges generated by a plurality of continuous pixel groups arranged in the vertical direction to the vertical transfer unit at the same time, and performs addition. An added luminance image signal can be generated. That is, between the unit pixel groups, a pixel that prohibits reading of charges to the vertical transfer unit (vertical shift register) is provided, and a plurality of charges generated in the unit pixel group are transferred to the vertical transfer unit at the same time. Since a plurality of charges are added for each group, a large output can be obtained.

  According to the fifth aspect of the present invention, since the vertical transfer pulses having the same phase are applied to the plurality of electrodes that are continuous in the vertical direction of the vertical transfer unit, the charges added in the vertical transfer unit are It becomes possible to perform vertical transfer at high speed.

  According to the sixth aspect of the present invention, the CCD color area sensor is large because a plurality of horizontal charges transferred to the horizontal transfer unit are added in the horizontal transfer unit or the output unit. Output can be obtained.

  According to the seventh aspect of the present invention, it is possible to obtain an added luminance signal that corresponds to the luminance of the subject and is close to an ideal monochrome camera output.

  According to the eighth aspect of the present invention, the image synthesizing unit reads the live view image signal and the added luminance image signal from the storage unit, and adds the added luminance signal to the luminance signal constituting the live view image signal, or Since the luminance signal composing the live view image signal and the added luminance signal are replaced, the luminance (illuminance) of the subject is lowered and the S / N (Signal / Noise) of the live view image signal is deteriorated. Below, the luminance signal constituting the live view image signal is added with the added luminance signal having a large output, or the luminance signal constituting the live view image signal is replaced with the added luminance signal having a large output. The S / N of the view image signal is improved, and a beautiful live view image can be visually recognized.

  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. FIG. 1A is a side view of a digital camera 1 that is an imaging apparatus according to the present invention, and FIG. 1B is a rear view of the digital camera 1. As shown in FIG. 1A, the digital camera 1 includes 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 body 2 includes an LCD monitor 211 formed by 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 color area sensor 251 described later is subjected to predetermined signal processing, and is displayed on the LCD monitor 211 and the EVF 210 and recorded on a recording medium such as a memory card 267 described later. Alternatively, processing such as image transfer to a personal computer is performed.

  As shown in FIG. 1A, a flash 212 that is hopped up when necessary is provided on the upper surface of the camera body 2. As shown in FIG. 1B, an LCD monitor 211 and an EVF 210 for displaying a captured image, reproducing and displaying a recorded image, and the like are provided at a substantially central portion on the back surface of the camera body 2.

A shutter button 201 is provided on the upper surface of the camera body 2 as shown in FIG. The shutter button 201 has a two-stage push stroke, and the AF control operation is executed by operating the shutter button 201. That is, as will be described later, the focus adjustment is roughly adjusted by setting the shutter button 201 to “half press”, and the focus adjustment is performed by changing the shutter button 201 from “half press” to “full press”. Is finely adjusted, and shooting (shooting for recording) is executed.
A mode setting dial 203 for setting the operation mode of the digital camera 1 is provided near the shutter button 201. The operation mode of the digital camera 1 set by the mode setting dial 203 includes “still image shooting mode”, “moving image shooting mode”, “playback mode”, and the like.

  The still image shooting mode is a mode for taking a picture from the shooting standby state to the shooting through the exposure control process, and the playback mode is for playing back and displaying the shot image recorded on the memory card 267 on the LCD monitor 211 or the EVF 210. Mode.

  Further, as shown in FIG. 1B, an electronic zoom button 209 for setting the electronic zoom zoom magnification is provided near the power switch 202 and the power switch 202 at the upper rear portion of the camera body 2. Is provided.

  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 / decision button 206 includes a jog dial key 204 for selecting various settings and a decision button 205 for confirming the setting selected with the jog dial 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 color area sensor 251 (hereinafter abbreviated as CCD 251) arranges R (red) light, G (green) light, and B (blue) light transmission filters in a checkered pattern in pixel units (pixel units). The subject light image formed by the lens unit 3 is photoelectrically converted by the color area imaging sensor thus selected, and image signals (R (red) light, G (green) light, and B (blue) light) of each color component ( For example, an interline element structure capable of reading out five fields. In addition to the conventional readout modes such as the above-described frame readout mode, live view readout mode, and AF readout mode, the CCD 251 has an addition readout mode for performing a pixel addition readout operation, which is necessary for each readout operation mode. The read signal is generated by a timing generator 256 described later.

  In the addition readout mode, when the luminance (illuminance) of the subject is lowered, the charges generated by a plurality of continuous pixels arranged in the vertical direction or a plurality of continuous pixels arranged in the horizontal direction are respectively used. This is a read mode in which vertical addition and horizontal addition are read out to generate an added luminance image signal. Then, by using the read addition luminance image signal having a large output as a signal for AF control which will be described later, a stable AF operation can be performed even when the luminance (illuminance) of the subject is lowered.

  In addition, by adding or replacing the read luminance image signal having a large output with the luminance signal constituting the live view image signal read under the live view readout mode as described later, Even when the luminance (illuminance) decreases, the S / N of the live view image signal is improved, and a beautiful live view image can be visually recognized.

  Here, the addition reading operation will be described. First, the vertical pixel addition operation will be described with reference to FIGS. FIG. 3 is a timing chart showing the vertical pixel addition operation.

  As shown in FIG. 3, in the readout period T1, transfer gate pulses (charge readout pulses) φTG3, φTG5, φTG7, and φTG9 superimposed on the vertical transfer pulses φV3, φV5, φV7, and φV9, respectively, are simultaneously output at time t1. The When the transfer gate pulses φTG3, φTG5, φTG7, and φTG9 are output, in FIG. 6, four consecutive pixels in the vertical direction to which the transfer gate pulses φTG3, φTG5, φTG7, and φTG9 are respectively applied are unit pixel groups 61B, 61C, Assuming 61D and 61E, the charges generated by the unit pixel groups 61B, 61C, 61D and 61E are simultaneously read out to the vertical shift register 63. In addition, a pixel 61F that prohibits reading of charges to the vertical shift register 63 is provided between one unit pixel group and another adjacent unit pixel group so that the charges added for each unit pixel group are not mixed. ing. The state at this time is shown in part B of FIG.

  Part B is a diagram schematically showing a vertical pixel addition operation. Here, m1 and m2 indicate column numbers of the vertical shift register 63, and n1 to n10 indicate row numbers of pixels arranged in the horizontal direction. When the transfer gate pulses φTG9, φTG7, φTG5, and φTG3 are simultaneously output, the pixel groups 61E corresponding to the n1 to n4 rows corresponding to the respective transfer gate pulses are generated by the pixel group 61D corresponding to the n6 to n9 rows. The charged charges are simultaneously read into the vertical shift registers 63 in the m1 and m2 columns. Further, n5 and n10 rows of pixels 61F that prohibit reading of charges are provided between the pixel groups 61E in the n1 to n4 rows and the pixel groups 61D in the n6 to n9 rows. The charges read out in units of four pixels in this way are added by the vertical shift register 63 and sequentially transferred to the horizontal shift register 64 in the vertical transfer period.

  In the vertical transfer period T2, as shown in FIG. 3, the charges added by the vertical shift register 63 are sequentially transferred to the horizontal shift register 64 by vertical transfer pulses φV1, φV3, φV5, φV7, and φV9 (from time t2 to time t2). t5). In order to perform vertical transfer at high speed, vertical transfer pulses having the same phase are applied to two electrodes that are continuous in the vertical direction. That is, the vertical transfer pulses φV3 and φV5 (time t2, t4) and φV7 and φV9 (time t3, t5) are set to the same phase. By performing high-speed vertical transfer in this way, the readout time of the added luminance image signal is shortened, and the live view readout mode and the addition readout mode described later are alternately switched for each frame to perform the readout operation of the image signal. This makes it possible to suppress a decrease in the frame rate of the live view image signal that occurs when it is performed.

Here, in the CCD 251, the charge amount generated in the pixel provided with the red transmission filter is R, the charge amount generated in the pixel provided with the green transmission filter is G, and the charge amount generated in the pixel provided with the blue transmission filter is generated. Assuming that the charges transferred to the horizontal shift register 64 are added by the vertical shift registers 63 of the B, m1 and m2 columns and transferred to the horizontal shift register 64, respectively, OS1 and OS2 are respectively expressed by the following (Equation 1), ( It is represented by Formula 2).
OS1 = 2 × R + 2 × G (Formula 1)
OS2 = 2 × B + 2 × G (Formula 2)
In this way, a large output image signal is obtained by vertically adding the four pixels.

  Next, the horizontal pixel addition operation will be described with reference to FIGS. FIG. 4 is a timing chart showing the horizontal pixel addition operation. FIG. 4A is a timing chart showing a method for reading out the charges transferred to the horizontal shift register 64 by conventional means. FIG. 4B is a timing chart showing a method of reading out the charges transferred to the horizontal shift register 64 by horizontal pixel addition.

  In the conventional reading method, as shown in FIG. 4A, the charges transferred from the vertical shift register 63 to the horizontal shift register 64 output the charges of each pixel for one horizontal line by the horizontal transfer pulses φH1 and φH2. The data are sequentially transferred to the unit 66. The output unit 66 is reset by a reset pulse φRS synchronized with the horizontal transfer pulses φH1 and φH2 after the charge V1 for one pixel in the horizontal direction is read by the horizontal transfer pulses φH1 and φH2 (t11), An image signal is output for each pixel.

  On the other hand, as shown in FIG. 4B, the method of reading by horizontal pixel addition divides the period of the reset pulse φRS by, for example, ½. In this way, the charges V2 for two pixels are transferred to the output unit 66 by the horizontal transfer pulses φH1 and φH2, added, and then reset (t20, t21). That is, the charges of two consecutive pixels arranged in the horizontal direction are added and read out as an image signal.

As shown in part B in FIG. 6, the charges OS1 and OS2 added by the vertical shift registers 63 in the m1 column and m2 column and transferred to the horizontal shift register 64, respectively, are subjected to horizontal pixel addition, thereby As shown in 3), the added luminance image signal Ya having a larger output can be obtained.
Ya = 2 × (R + 2 × G + B) (Formula 3)
The added luminance image signal Ya obtained in this manner is a luminance signal corresponding to the luminance of the subject and close to the output of an ideal monochrome camera.

In this embodiment, by adding 4 pixels in the vertical direction and 2 pixels in the horizontal direction, the added luminance image signal shown in (Equation 3) is generated. By selecting the number of added pixels, the following As shown in (Expression 4), it is also possible to obtain a luminance signal close to the output of an ideal black and white camera with the output level being variable.
Ya = n * (R + 2 * G + B) (Formula 4)
In the formula, n represents an arbitrary positive integer.

  Here, returning to the description of the control system of the digital camera 1, the timing generator 256 is based on a reference clock transmitted from a reference clock generator 264 described later and a read mode control signal transmitted from the read mode controller 273. Thus, a drive control signal for the CCD 251 is generated. The drive control signal generated by the timing generator 256 includes, for example, an integration start / end timing signal for controlling the exposure start and end timings in the CCD 251 and each pixel corresponding to the above-described plural types of readout operation modes. Clock signals such as readout signals (horizontal synchronization signal, vertical synchronization signal, transfer signal, etc.) for reading out charges can be cited. When these clock signals are supplied to the CCD 251, the CCD 251 performs drive control corresponding to each clock signal. Done.

  The signal processing circuit 252 includes a CDS circuit 253 and an AGC circuit 254, and predetermined processing is performed on the image signal via these components. Hereinafter, the predetermined processing for the image signal performed by the signal processing circuit 252 will be described.

  A CDS (correlated double sampling) circuit 253 performs reduction of noise generated during reading from an image signal read from the CCD 251 and correction of dark noise by an OB clamping operation.

  An AGC (automatic gain control) circuit 254 adjusts the gain of the image signal processed by the CDS circuit 253.

  The A / D converter 255 converts each pixel signal constituting the image signal input from the AGC circuit 254 into a digital signal. The A / D converter 255 converts each pixel signal of the analog signal into, for example, a 14-bit digital signal based on the A / D conversion clock input from the reference clock generation unit 264.

  In this manner, the image signal read by the CCD 251 is subjected to predetermined processing by the signal processing circuit 252 and the A / D converter 255, 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 controls the photographing operation of the digital camera 1 by controlling the operation of each member constituting the camera main body 2 and the lens unit 3 described above. 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 265 in synchronization with the reading of the image signal output from the CCD 251. That is, a digital image signal used for processing performed by the image processing CPU 261 is once recorded in the image memory 265 and taken out from the image memory 265 and used for processing in each block.

  As described above, the image memory 265 functions as a storage unit in the imaging apparatus according to the present invention.

  As shown in FIG. 2, the image processing CPU 261 includes, for example, an image processing unit 262 including a pixel interpolation unit, a resolution conversion unit, a white balance control unit, a gamma correction unit, a matrix calculation unit, an image compression unit, and an image composition unit 263. The image processing unit 262 includes a reference clock generation unit 264. The image processing unit 262 performs known image signal processing on the digital image signal extracted from the image memory 265. Then, the digital image signal that has undergone predetermined processing at these parts is stored in the image memory 265 again.

  The reference clock generation unit 264 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 in the timing generator 256, an A / D conversion clock used in the A / D converter 255, and the like. Generate a clock.

  Next, the image synthesis unit 263 functions as an image synthesis unit that synthesizes the live view image signal read from the image memory 265 and the added luminance signal. The image composition unit 263 performs addition that has a large output to the luminance signal constituting the live view image signal even under the situation where the luminance of the subject is reduced and the S / N (Signal / Noise) of the live view image signal is deteriorated. By adding or replacing the luminance signal, the S / N of the live view image signal is improved, and a beautiful live view image can be visually recognized. Details of the image composition unit 263 will be described later.

  Next, the LCD monitor 211 and the EVF 210 display the image signals read from the image memory 265 by the image processing CPU 261 as field images via the LCD driver 268 and the EVF driver 269, respectively. As described above, the LCD monitor 211 and the EVF 210 function as a display unit in the imaging apparatus according to the present invention.

  The camera control CPU 270 is composed of a microcomputer, and based on switch signals generated by switch operations of a switch group 275 to be described later, the camera body CPU 2 and the lens unit 3 are sequentially controlled to drive the digital camera 1. Centrally control the operation.

  The camera control CPU 270 also determines the luminance value of the subject calculated by the AE (Auto Exposure) control unit 271 and AE control unit 271 that perform exposure control of the digital camera 1 based on the image signal read from the CCD 251. A luminance determination unit 272 for determining, a read mode control unit 273 for controlling a read signal generated by the timing generator 256 based on the determination result determined by the luminance determination unit 272, and AF (Auto Focus) control of the digital camera 1 It is composed of an AF control unit 274 that performs the function, and functions as a CCD color area sensor control means. Hereinafter, operations performed in each part will be described.

  The AE control unit 271 performs exposure control of the digital camera 1 based on the image signal read from the CCD 251. The exposure control is performed as follows.

  First, image data relating to a preset photometric area on the imaging surface is read from the image data captured by the CCD 251 and written into the image memory 265, and exposure control data is calculated based on the read image data. Then, exposure time data is calculated based on the calculated exposure control data and preset program diagram data. Based on the calculated exposure time data, the timing generator 256, the AGC circuit 254, and the aperture / shutter driver 257 are calculated. The proper exposure amount to the CCD 251 is controlled.

  In the present invention, the AE control unit 271 also functions as a detection unit that detects the luminance of the subject.

  The luminance determining unit 272 determines the luminance level (degree of brightness) of the subject based on the luminance information sent from the AE control unit 271.

  The read mode control unit 273 controls the read signal generated by the timing generator 256 based on the determination result sent from the luminance determination unit 272.

  Next, the AF control unit 274 performs AF control of the digital camera 1 based on the image signal read from the CCD 251, and the AF control is performed as follows.

  First, when the shutter button 201 is “half-pressed”, the image is captured by the CCD 251 under the readout mode set by the readout mode control unit 273 according to the luminance (illuminance) of the subject, as will be described later. From the image data written in the memory 265, image data relating to a preset distance measurement area on the imaging surface is read out, distance measurement is performed based on the read image data, and a focus / zoom motor is based on the result. The operation of the driver 258 is controlled to perform rough AF adjustment in the digital camera 1. Next, when the shutter button 201 is set to “full press”, the read mode control unit 273 resets the read mode according to the luminance (illuminance) of the subject and is the same as when the shutter button 201 is “half pressed”. AF fine control is performed through the operation.

  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 251, and records the image signal subjected to the processing in the image memory 265. .

  The digital camera 1 according to the present invention records the image signal captured from the CCD 251 under the mode set by the mode setting dial 203 in the image memory 265 or displays it on the LCD monitor 211 or EVF 210.

  The switch group 275 in FIG. 2 corresponds to the shutter button 201, the power switch 202, the mode setting dial 203, the selection / decision button 206, the menu button 207, the quick view button 208, the electronic zoom button 209, and the like in FIG. Switch.

  Here, the read mode control operation performed by the digital camera 1 according to the present invention will be described with reference to the flowchart shown in FIG. 5 and the timing chart of the read operation shown in FIG. 8A shows an image signal output from the CCD 251 when the readout operation is performed by alternately switching between the addition readout mode and the live view readout mode, and FIG. 8B shows the addition luminance read out from the image memory 265. (C) shows a live view image signal read from the image memory 265. Further, (d) shows a color image signal synthesized by the image synthesis unit 263.

  First, when the digital camera 1 is set to the still image shooting mode with the mode setting dial 203, the readout mode control unit 273 sets the live view readout mode, and the live view image is displayed on the LCD monitor 211 and the EVF 210 of the digital camera 1. Is displayed (step S1).

  Next, when the shutter button 201 is “half-pressed” (step S <b> 2), the AE control unit 271 performs live for a photometric area on the imaging surface set in advance from live view image data written in the image memory 265. The view image data is read, and based on the read live view image data, the brightness (Bv value) of the subject is detected by an exposure control expression expressed by (Expression 5) described later (step S3). Then, the detected luminance information is sent to the luminance determination unit 272.

Specifically, live view image data relating to a preset photometric area on the imaging surface is read from the live view image data written in the image memory 265, and based on the read live view image data, the following (formula 5) ), The brightness (Bv value) of the subject can be detected, and the detected brightness information is sent to a brightness determination unit 272 described later. The luminance determination unit 272 determines the luminance level (degree of brightness) of the subject based on the luminance information sent from the AE control unit 271. As described above, the AE control unit 271 detects the luminance (brightness) of the subject in the imaging apparatus according to the present invention.
Bv = Tv−Sv + Av (Formula 5)
In the equation, Bv represents subject brightness, Tv represents a shutter speed value set by the timing generator 256, Sv represents a photographing sensitivity value set by the AGC circuit 254, and Av represents an aperture value set by the aperture / shutter driver 257. Is.

  The luminance determination unit 272 determines the luminance level (degree of brightness) of the subject based on the luminance information sent from the AE control unit 271 (step S4). Then, the determination result is sent to the read mode control unit 273.

  Specifically, the luminance determination unit 272 has, for example, two reference luminance values B1 and B2 having the following relationship (Equation 6), and the luminance value of the subject sent from the AE control unit 271: By comparing with the reference luminance value, the luminance level (degree of brightness) of the subject is determined as shown below (Table 1). Then, the determination result is sent to a read mode control unit 273 described later.

  B1> B2 (Formula 6)

Here, B in Table 1 indicates the luminance value of the subject detected by the AE control unit 271.

  When the determination result sent from the luminance determination unit 272 to the readout mode control unit 273 is level 1 or 2 (step S5; Yes), the AF control unit 274 performs rough AF adjustment using the live view image signal. It performs (step S6).

  Next, the shutter button 201 is set to “full press” (step S7). When the determination result sent from the luminance determination unit 272 is level 1 (step S8; Yes), the read mode control unit 273 reads the image at a high frame rate as described above because the luminance of the subject is high. Even if it is performed, the AF read mode is set because the signal level necessary for the AF control is obtained (step S9). Then, a read mode control signal corresponding to the AF read mode is sent to the timing generator 256. The timing generator 256 generates a read signal for the CCD 251 based on the read mode control signal sent from the read mode control unit 273, drives the CCD 251, and reads an image signal from the CCD 251 (step S10). Then, the AF control unit 274 performs AF fine adjustment using the image signal read in the AF read mode (step S11). In this way, when the luminance of the subject is high, the AF control is speeded up and a color image display at a high frame rate is realized.

  Further, when the determination result sent from the luminance determining unit 272 is level 2 (step S8; No), the reading mode control unit 273 reads out at a high frame rate since the luminance of the subject is low. Then, since the signal level necessary for AF control cannot be obtained as described above, the live view readout mode having a frame rate slower than that of the AF mode is reset as the readout operation mode without setting the AF mode ( Step S12). Then, the same processing as step S10 in the case of level 1 is performed, and an image signal is read out from the CCD 251 (step S13), and the AF control unit 274 performs AF using the image signal read out in the AF reading mode. Fine adjustment is performed (step S14). In this way, when the luminance of the subject decreases, stable AF control is performed by using the live view image signal read from the CCD 251 as the AF control image signal under the live view read mode. Can do.

  Next, when the determination result sent from the luminance determination unit 272 is level 3 (step S5; No), the reading mode control unit 273 reads out in the live view reading mode because the luminance of the subject is extremely low. Since the signal level required for AF control cannot be obtained even with the image signal, the addition readout mode and the live view readout mode, which can obtain a higher signal level than the live view readout mode, are switched alternately for each frame. As described above, the read operation mode is set (step S15). Then, the same processing as step S10 in the case of level 1 is performed, and an image signal is read from the CCD 251 (step S16). At this time, as shown in FIG. 8A, the CCD 251 reads the live view image signal (first frame) read in the live view read mode period Tl and the added luminance read in the add read mode period Ta. A signal (second frame) is alternately output for each frame. Further, as described above, in the addition readout mode period Ta, the high-speed vertical transfer is performed, so that the addition readout mode period Ta is shorter than the live view readout mode period Tl.

  In this way, in the image signal read from the CCD 251 under the two read modes, the AF control unit 274 performs rough AF adjustment using the added luminance image signal read in the added read mode period Ta. (Step S17).

  The live view image signal read out in the live view readout mode period Tl is subjected to predetermined processing in an image composition unit 263 described later, and then displayed on the display unit such as the LCD monitor 211 and the EVF 210. Is used to display an image (step S18).

Next, when the shutter button 201 is “fully pressed” (step S19), the read mode control unit 273 sets the addition read mode as the read operation mode (step S20). Then, the same processing as step S10 in the case of level 1 is performed, and an image signal is read from the CCD 251 (step S21), and the AF control unit 274 uses the image signal read in the addition reading mode to perform AF. Fine adjustment is performed (step S22).
Here, the generation of the display image signal performed by the image composition unit 263 in step S18 will be specifically described.
The image synthesizing unit 263 switches the live view readout mode and the addition readout mode alternately for each frame, reads the luminance from the image memory 265 temporarily stored with the live view image signal and the addition luminance image signal read from the CCD 251. A live view image signal composed of a signal and a color signal and an added luminance image signal composed of an added luminance signal are read, and the added luminance signal is added to the luminance signal constituting the live view image signal, or the luminance signal constituting the live view image signal. And the added luminance signal.

When the live view image signal read from the image memory 265 in step S16 in the live view read mode is S, the luminance signal constituting the live view image signal S is Yl, and the color signal is C, the live view image signal S is It is represented by the following (formula 7). At this time, the live view image signal read from the image memory 265 is shown in FIG.
S = Yl + C (Formula 7)
Also, assuming that the added luminance image signal (added luminance signal) read from the image memory 265 under the addition readout mode in step S16 is Ya, the image composition unit 263 has the following (Equation 8) or (Equation 9). As shown in FIG. 4, the added luminance signal Ya is added to the luminance signal Yl constituting the live view image signal S, or the luminance signal Yl constituting the live view image signal S and the added luminance signal Ya are replaced with a new color. The image signal S1 or S2 is generated. At this time, the newly generated color image signal S1 or S2 is shown in FIG.
S1 = (Yl + Ya) + C (Formula 8)
S2 = Ya + C (Formula 9)
In this way, by performing image display based on the color image signal S1 or S2 newly generated using the added luminance signal Ya having a large output, even when the luminance of the subject is extremely low, S / A beautiful live view image with improved N can be visually recognized. That is, even when the luminance of the subject is extremely reduced, stable AF control is performed by using the added luminance image signal with increased sensitivity read out from the CCD 251 under the addition readout mode as the image signal for AF control. Can do. In the display unit, the live view image signal read from the CCD 251 under the live view mode is used as a display image signal, so that a color live view image can be displayed.

  As described above, the imaging apparatus according to the present invention can display a clear color image while maintaining stable AF performance even when the luminance (illuminance) of the subject is lowered.

1 is a schematic external view of a digital camera according to the present invention. 1 is a circuit block configuration diagram of a digital camera according to the present invention. 4 is a timing chart of vertical pixel addition in the digital camera according to the present invention. 4 is a timing chart of horizontal pixel addition in the digital camera according to the present invention. 4 is a flowchart showing a flow of a read mode control operation in the digital camera according to the present invention. It is a schematic diagram which shows the structure of CCD of the digital camera concerning this invention. It is a schematic diagram which shows the read-out area | region of AF mode of CCD in the digital camera concerning this invention. 3 is a timing chart of a reading operation in the digital camera according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Digital camera 2 Camera body part 201 Shutter button 202 Power switch 203 Mode setting dial 204 Jog dial key 205 Enter button 206 Select / Set button 207 Menu button 208 Quick view button 209 Electronic zoom button 210 Electronic viewfinder (EVF)
211 LCD monitor 212 Flash 251 CCD color area sensor 252 Signal processing circuit 253 CDS circuit 254 AGC circuit 255 A / D converter 256 Timing generator 257 Aperture / shutter driver 258 Focus / zoom motor driver 261 Image processing CPU
262 Image processing unit 263 Image composition unit 264 Reference clock generation unit 265 Image memory 266 Memory card driver 267 Memory card 268 LCD driver 269 EVF driver 270 Camera control CPU
271 AE control unit 272 Luminance determination unit 273 Reading mode control unit 274 AF control unit 275 Switch group 3 Lens unit 301 Aperture / shutter 302 Focus / zoom motor 60 CCD
61 Photodiode (photoelectric conversion element)
62 Light receiving area 63 Vertical transfer unit (vertical shift register)
64 Horizontal transfer section (horizontal shift register)
65 Charge drain 66 Output section

Claims (8)

A CCD color area sensor that photoelectrically converts a subject light image with a plurality of photoelectric conversion elements arranged two-dimensionally to generate an image signal, and an image is displayed based on the image signal generated by the CCD color area sensor An image pickup apparatus comprising: a display unit; an autofocus control unit that performs autofocus control based on an image signal generated by the CCD color area sensor; and a detection unit that detects luminance of a subject.
When the luminance of the subject detected by the detection means is low,
The CCD color area sensor reads out charges from a plurality of photoelectric conversion elements arranged in the vertical direction for each predetermined number of photoelectric conversion elements, generates a live view image signal, and displays the live view image signal on the display unit. A first frame for displaying an image based on a view image signal;
The CCD color area sensor adds and reads out the charges generated by a plurality of continuous photoelectric conversion elements arranged in the vertical direction or a plurality of continuous photoelectric conversion elements arranged in the horizontal direction, and adds them. An image pickup apparatus comprising: a CCD color area sensor control unit that generates a luminance image signal and executes a second frame for causing the autofocus control unit to perform autofocus control based on the added luminance image signal . The image pickup apparatus according to claim 1, wherein the CCD color area sensor control unit alternately executes the first frame and the second frame. The frame rate of the added luminance image signal read out in the second frame is higher than the frame rate of the live view image signal read out in the first frame. The imaging device described in 1. The CCD color area sensor has an interline element structure capable of multi-field readout of 3 fields or more,
A vertical transfer unit that sequentially transfers charges accumulated in a plurality of continuous photoelectric conversion elements arranged in the vertical direction in the vertical direction;
A plurality of continuous photoelectric conversion elements arranged in the vertical direction are used as a unit pixel group, and provided between the first unit pixel group and a second unit pixel group adjacent to the first unit pixel group. , Forbidden pixels that prohibit the reading of charges to the vertical transfer unit,
2. The CCD color area sensor control means transfers a plurality of electric charges generated in the unit pixel group to the vertical transfer unit at the same time, performs addition, and generates the added luminance image signal. The imaging device described in 1. The imaging apparatus according to claim 4, wherein vertical transfer pulses having the same phase are applied to a plurality of electrodes that are continuous in a vertical direction of the vertical transfer unit. The CCD color area sensor adds a plurality of horizontal charges transferred to a horizontal transfer unit in the horizontal transfer unit or output unit to generate the added luminance image signal. The imaging apparatus according to 1. In the CCD color area sensor, the amount of charge generated in a pixel provided with a red transmission filter is R, the amount of charge generated in a pixel provided with a green transmission filter is G, and a pixel provided with a blue transmission filter is used. The following relationship is satisfied, where B is the generated charge amount, Ya is the added luminance image signal, and n is an arbitrary positive integer: 7. The imaging device described in 1.
Ya = n × (R + 2 × G + B) Storage means for temporarily storing the live view image signal and the added luminance image signal read by the CCD color area sensor;
The live luminance image signal composed of the luminance signal and color signal temporarily stored in the storage means and the additional luminance image signal composed of the additional luminance signal are read out, and the additional luminance signal is included in the luminance signal constituting the live view image signal. Image synthesis means for adding or replacing the luminance signal constituting the live view image signal and the added luminance signal;
The imaging apparatus according to claim 1, wherein the imaging apparatus includes:

Images