JP4612848B2 - Imaging apparatus and control method thereof - Google Patents

Description

  The present invention relates to an imaging apparatus using an imaging element such as a CCD or a CMOS image sensor, and a control method thereof.

  2. Description of the Related Art Conventionally, imaging devices such as digital cameras and video cameras using imaging elements such as CCDs and CMOS image sensors have become widespread.

  FIG. 6 is a block diagram showing the configuration of a conventional digital camera or digital video camera. Reference numeral 101 denotes an image sensor, and a CCD or CMOS sensor is generally used. Reference numeral 102 denotes an A / D converter that converts an analog signal from the image sensor 101 into a digital signal. Reference numeral 103 denotes a DSP (Digital Signal Proseccer) that performs various correction processes and development processes on data from the A / D converter 102. In the DSP 103, various memories such as the ROM 106 and the RAM 107 are controlled and image data is written to the recording medium 108.

  A timing generation circuit 104 supplies a clock signal and a control signal to the image sensor 101, the A / D converter 102, and the DSP 103, and is controlled by the CPU 105. Reference numeral 105 denotes a CPU that controls the DSP 103 and the timing generation circuit 104, and controls camera functions using various units (not shown) such as photometry and distance measurement. Switches 109 to 111, which will be described later, and a mode dial 112 are connected, and processing corresponding to each state is executed.

  A ROM 106 stores a camera control program executed by the CPU 105 and various correction data used by the DSP 103, and a RAM 107 temporarily stores image data and correction data processed by the DSP 103. The RAM 107 can be accessed at a higher speed than the ROM 106. Reference numeral 108 denotes a recording medium such as a compact flash (registered trademark) card for storing a photographed image, which is connected to a camera via a connector (not shown).

  Reference numeral 109 denotes a power switch (SW) for activating the camera, and 110 is turned on by a first predetermined operation (for example, half-press) of a shutter button (not shown), and instructs to start operations such as photometry processing and distance measurement processing. The shutter switches SW 1 and 111 are turned on by a second predetermined operation (for example, full press) of a shutter button (not shown), drive a mirror and a shutter (not shown), and a signal read from the image sensor 101 is converted into an A / D converter. 102, a shutter switch SW2 for instructing the start of a series of imaging operations to be written to the recording medium 108 via the DSP 103.

  FIG. 7 is a flowchart showing control of the imaging apparatus having the configuration shown in FIG. First, in step S101, it is determined whether or not the power SW 109 for starting the camera is turned on. If it is off, step S101 is repeated. If the power SW 109 is turned on, it is determined in step S102 whether or not the mode dial 112 is set to the shooting mode. If the other mode is set, the process corresponding to the mode selected in step S103 is performed and then the process returns to step S101. If the shooting mode is set, the process proceeds to step S104.

  In step S104, it is determined whether the shutter switch SW1 (110) is ON. If SW1 (110) is OFF, the process returns to step S101 and the above-described processing is repeated. If SW1 (110) is ON, the process proceeds to step S105.

  In step S105, using a photometry control unit and a distance measurement control unit (not shown), photometry processing for determining the aperture value and shutter speed and distance measurement processing for adjusting the photographing lens focus to the subject are performed.

  When the photometry / ranging process in step S105 is completed, the state of the shutter switch SW2 (111) is determined in a subsequent step S106. If SW2 is OFF, the process returns to step S104 and the above-described processing is repeated. If SW2 is ON, shooting processing is executed in step S107. Details of this photographing process will be described later.

  When the photographing process in step S107 is completed, the process proceeds to step S108, and the DSP 103 performs development processing on the photographed image data. In step S109, the image data that has undergone development processing is subjected to compression processing, and the compressed image data is stored in an empty area of the RAM 107.

  In step S110, the image data stored in the RAM 107 is read out and recording processing on the recording medium 108 is executed. After the recording process is completed, the process returns to step S101 to prepare for the next process.

  Next, details of the photographing processing operation performed in step S107 will be described with reference to FIG.

  First, in step S201, the mirror is moved to the mirror up position, and in step S202, the aperture is driven to a predetermined aperture value based on the photometric data obtained by the photometric processing in step S105 of FIG. In step S203, the charge clear operation of the image sensor 101 is performed, and charge accumulation is started in step S204. After the start of charge accumulation, the shutter is opened in step S205, and exposure of the image sensor 101 is started (step S206).

  Thereafter, in step S207, the process waits for the end of exposure according to the photometric data, and the shutter is closed in step S208. In step S309, the aperture is driven to the open aperture value, and in step S210, the mirror is driven to the mirror down position. In step S211, the process waits until the set charge accumulation time elapses, and ends the charge accumulation of the image sensor 101 (step S212). Finally, in step S213, the signal of the image sensor 101 is read out, and a series of processing is terminated and the processing returns to the main processing.

  The above is a description of a series of camera operations.

  In an imaging apparatus using an imaging element, a method using a plurality of readout lines (channels) is generally known in order to shorten a signal readout time and increase a continuous shooting speed. FIG. 9 shows an example in which the image sensor 101 is configured with a plurality of channels (here, two channels). Reference numerals 401a, 401b, 403a, and 403b are all pixels constituting the image sensor 101, and are arranged in a lattice shape as shown in the figure. Each of these pixels is provided with one of R, G, and B color filters. For example, the color filters are arranged so that a row repeating RG in the horizontal direction and a row repeating GB are alternately repeated in the vertical direction. ing. Reference numerals 402a, 402b, 404a, and 404b denote switches, which transfer pixel signals of respective columns to readout lines 405a and 405b. 406a and 406b are amplifiers for amplifying and outputting the pixel signals transferred to the readout lines 405a and 405b.

  In the image sensor 101 having the above-described configuration, pixel signals are sequentially read out row by row. First, the switches 402a and 402b are turned on, and the signals of the pixels 401a and 401b are transferred to the amplifiers 406a and 406b via the readout lines 405a and 405b, respectively. Subsequently, the switches 404a and 404b are turned on, the signals of the pixels 403a and 403b are transferred to the readout lines 405a and 405b, and output through the amplifiers 406a and 406b as before. When the pixel signals for one row have been read out by such repetition, the signals in the next row are similarly read in order.

  When a plurality of readout lines (channels) are used in this way, pixels corresponding to the number of channels can be read out simultaneously, so that the signal readout time can be shortened and the continuous shooting speed can be increased.

  Further, in the image pickup device, an offset clamp process is generally performed in order to remove the dark current component and adjust the dark offset level to a desired output level. This offset clamp processing circuit is provided in the sensor or in an A / D converter for analog-digital conversion of the output signal of the image sensor.

  In an imaging apparatus having a multi-channel configuration as described above, an offset between channels with different dark levels may occur for each channel due to a difference in circuit offset. The channel-to-channel offset deteriorates the image quality of the captured image as noise and causes a white balance calculation to be erroneous.

  In some cases, an offset clamp circuit is provided for the purpose of removing such circuit offset components and pixel dark current components (see, for example, Patent Document 1).

  In Patent Document 1, the OB portion is provided in the left and right regions of the effective pixel portion (the pixel region used as the image signal of the captured image) of the image sensor, and the pixel value of the OB portion obtained for each line is used. To correct the black level.

JP 2002-335454 A

  Since the offset between channels may change with changes in conditions such as temperature and accumulation time as time passes, it is desirable to calculate and correct an offset correction value for each captured image data. However, since it takes time to calculate the offset correction value, there is a problem that it is difficult to perform correction in real time at the time of shooting.

  For example, in the configuration of Patent Document 1 described above, since the offset correction value is calculated for each line using the pixel value of the OB portion, in an imaging apparatus in which the correction value calculation speed is slower than the reading speed of the image sensor. The reading speed of the image sensor must be slowed down in accordance with the calculated speed, and the reading speed of the image sensor cannot be fully utilized.

  In addition, a method of writing the pixel signal read from the image sensor to the RAM 107 once including the signal of the OB portion without performing the offset correction, and reading the written pixel signal again to correct the offset is also conceivable. Although the reading speed of the element can be increased, it takes time to write and read the pixel signal, so that the time required for the throughput becomes long. In addition, in order to reduce the time required for the offset correction processing, when correction is performed using an offset correction value calculated in the past, the offset between channels is affected by temperature changes, noise, defective pixels of the image sensor, etc. May occur.

  The present invention has been made in view of the above-described problems, and enables appropriate offset correction corresponding to changes in conditions such as temperature and accumulation time in real time without reducing the readout speed of the image sensor as much as possible. For the purpose.

In order to achieve the above object, an image pickup apparatus according to the present invention includes a first region in which a pixel signal serving as a reference for offset correction is read, and a second signal from which a pixel signal used as an image signal is read . An image pickup device including a region, a drive signal generation unit that generates a drive signal for reading a pixel signal from the image pickup device, a calculation unit that calculates an offset correction value based on the pixel signal of the first region, and offset correction Symbol value you store憶means, by using the offset correction value the storage, and an offset correcting means for correcting the pixel signal read from the second region, after the read end of the pixel signal of the first region said drive signal generating means is controlled to stop the generation of the drive signal, the offset correction value based on the pixel signals of the first region read the Detecting means calculates the calculated the offset correction value is controlled to be stored in the storage means, after storage in the memory means of the offset correction value, resuming generation of said drive signal generating means said drive signal to, and a control Gosuru control means to read out pixel signals of the second region.

Also, it is composed of a plurality of pixels, a first region where the pixel signal as a reference of the offset correction is read, and an image pickup element and a second region where the pixel signal to be used as the image signal is read out, the pixel from the image sensor The control method of the present invention for an imaging apparatus having a drive signal generating means for generating a drive signal for reading a signal includes a first readout step of reading out a pixel signal of the first region, and a pixel signal of the first region . a drive stop step of stopping the driving signal generating means generates the drive signal after the read end, a calculation step of calculating the offset correction value based on the picture element signal of the first region, calculated in the calculating step wherein the offset correction value storing means SL you stored in憶step, after storage in the memory means of the offset correction value in the storage step, said drive signal generating means Using serial resuming driving restart process the generation of driving signals, and a second reading step of reading the pixel signal of the second region, the offset correction value said storage, corrects the pixel signal read from the second region Offset correction step.

  According to the present invention, appropriate offset correction corresponding to changes in conditions such as temperature and storage time can be performed in real time without reducing the readout speed of the image sensor as much as possible.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings.

<First Embodiment>
FIG. 1 is a block diagram illustrating a configuration of an imaging apparatus according to the first embodiment of the present invention. In addition, the same reference number is attached | subjected to the structure similar to FIG. 6, and description is abbreviate | omitted. In FIG. 1, reference numeral 508 denotes an OB unit integrating circuit, and among the pixel signals read from the image sensor 101 via the A / D converter 102, a light-shielded portion of the pixel (Optical Black, hereinafter referred to as “OB unit”). )) Is integrated. Reference numeral 509 denotes an offset correction unit of the DSP 103, which includes a subtracter 510 and a RAM 511 that holds correction values. The signal that has passed through the offset correction unit 509 is written into the RAM 107 for temporary storage of image data.

  The basic operation of the imaging apparatus according to the first embodiment having the above-described configuration is the same as that described with reference to FIGS. 7 and 8, but is characterized by the imaging signal readout process performed in step S213 in FIG. Therefore, the specific operation will be described below with reference to the flowchart of FIG.

  When charge accumulation in the image sensor 101 is completed by the operation up to step S212 in FIG. 8, first, in step S301, output of a drive signal for reading a pixel signal from the image sensor 101 is started. FIG. 3 is a conceptual diagram showing a pixel region of the image sensor 101, and reading is performed row by row from the upper side of the image sensor 101. At this time, the image data written to the RAM 107 through the offset correction unit 509 includes an offset component.

  When the reading reaches the integration start line shown in FIG. 3, integration of signals in a predetermined area of the OB portion is started in step S302. This integration operation is performed using the OB unit integration circuit 508 of the DSP 103. The integration region can be set in advance by register setting.

  In subsequent step S303, the operation is continued until all the pixel signals in the integration region are read out. When the readout reaches the end row of the integration region and all the integration regions are read out, the integration operation is ended in step S304.

  After the integration is completed, the drive signal for the image sensor 101 is stopped in step S305, and the reading operation is interrupted. After the reading is interrupted, the DSP 103 calculates an offset correction value from the integration result of the OB unit integration circuit 508 in step S306. As this correction value calculation, for example, a method of calculating an average value of the OB portion from the integration result and taking a difference between the average value and a desired dark level can be considered. Of course, it goes without saying that the present invention is not limited by the offset correction value calculation method, and the offset correction value may be calculated by a method suitable for the configuration of the imaging apparatus.

  After calculating the offset correction value, in step S307, the calculated correction value is set in the RAM 511 of the offset correction unit 509. Subsequently, the drive signal output is restarted in step S308, and the aperture (exposure region) of the image sensor 101 is included. Read the remaining part. The offset component is removed by the subtractor 510 from the pixel signal read after the resumption of reading in step S308 using the offset correction value set in the RAM 511, and is written in the RAM 107.

  In step S309, the drive signal is output up to the last row of the image sensor 101, and the readout of the image signal is terminated.

  FIG. 4 is a timing chart of the reading operation of the imaging apparatus described above.

  The vertical synchronization signal and the horizontal synchronization signal are signals given from the DSP 103 to the timing generation circuit 104. The vertical synchronization signal instructs the start of reading one screen, and the horizontal synchronization signal represents the time in units of one row.

  The vertical shift register drive signal is a signal for driving the vertical shift register for switching the selected row of the image sensor 101, and is generated by the timing generation circuit 104 based on the horizontal synchronization signal. The horizontal shift register drive signal is a horizontal shift register drive signal for switching the selected column when reading out each row of the image sensor 101, and is generated by the timing generation circuit 104 based on the horizontal synchronization signal.

  As shown in FIG. 4, at the time t <b> 1, the DSP 103 outputs a vertical synchronizing signal and starts outputting a horizontal synchronizing signal at a constant period when reading is started in step S <b> 304 in FIG. 2. The timing generation circuit 104 outputs vertical and horizontal shift register drive signals based on the horizontal synchronization signal. The timing generation circuit 104 continues to output the vertical and horizontal shift register drive signals even after reaching the integration start row at t2. When the reading operation reaches the integration end line at t3, the DSP 103 stops outputting the horizontal synchronization signal until the offset correction value calculation is performed and the reading is resumed (corresponding to step S306 in FIG. 2) (FIG. 2). 2 corresponds to step S305 in FIG. As a result, the output of the vertical and horizontal shift register drive signals in the timing generation circuit 104 is also stopped, and the read operation is interrupted. Note that although the vertical and horizontal shift register drive signals are described here as examples, other image sensor drive signals generated by the timing generation circuit 104 are also stopped as a matter of course.

  When the setting of the offset correction value is completed at t4 (corresponding to step S307 in FIG. 2), the horizontal synchronization signal is output again from the DSP 103, and the reading operation is resumed (corresponding to step S308 in FIG. 2). As described above, the pixel signal read after this is subjected to offset correction using the set offset correction value.

  As described above, according to the first embodiment, before reading the pixel signal of the opening of the image sensor, the reading is temporarily interrupted to calculate the offset correction value, and the obtained offset correction value is used. In order to process the pixel signal of the effective image area (opening) that has been continuously read out in real time, the image data once written in the RAM 107 is read and corrected again for offset correction without performing offset correction as in the prior art. Compared to the case, the time from reading of the image sensor to the end of offset correction can be shortened.

  In addition, offset correction values obtained at the same timing as the captured image can be used, so changes in conditions such as temperature and storage time are also supported compared to correction using offset correction values calculated in the past. It becomes possible to perform more accurate offset correction.

  Furthermore, compared to the case where no offset correction is performed, only the time required for calculating the offset correction value is increased, so that the offset correction can be performed at a high speed while taking full advantage of the reading speed of the image sensor. Even when shooting, the continuous shooting speed is hardly affected.

  In the above-described embodiment, the case where reading of the image sensor 101 is interrupted once when reading of the integration region is completed has been described. However, the horizontal synchronization signal is output even after the calculation of the offset correction value is started. The remaining OB portion is read, and when the offset correction value has been calculated when the aperture (exposure region) in FIG. 3 is reached, the output of the horizontal synchronizing signal may be stopped. .

  When the image sensor 101 is a CMOS sensor and has a configuration in which a readout row can be arbitrarily selected, first, only the integration region in FIG. 3 is read out to calculate an offset correction value, and after the offset correction value is acquired, FIG. Reading may be started immediately from the opening.

  In addition, the timing generation circuit 104 may stop the driving signal of the image sensor 101 including the vertical and horizontal shift register driving signals without stopping the horizontal synchronization signal. In this case, the DSP 103 or the CPU 105 gives a signal notifying the timing generation circuit 104 of the calculation start of the offset correction value and the completion of the setting.

  Alternatively, a drive signal stop period sufficient to calculate an offset correction value may be determined by register setting of the timing generation circuit 104 without using an offset correction value setting completion signal.

<Second Embodiment>
Next, a second embodiment of the present invention will be described.

  In the second embodiment, an image sensor with two-channel reading as shown in FIG. The imaging device in that case is shown in FIG. As shown in FIG. 5, in the second embodiment, two systems of OB integration circuits 508 and offset correction units 509 shown in FIG. 1 are provided, and the average value of the OB part of each channel is set to a desired dark level. An offset correction value is set so that The same reference numerals are given to the same components as those in FIG. 1. In the configuration corresponding to the channel 1, “−1” is added after the reference number shown in FIG. Adds “−2”.

  The operation of the imaging apparatus of the second embodiment having the configuration shown in FIG. 2 is the same as that of the first embodiment described above with reference to FIG. This is the same as in the first embodiment.

  Note that the offset correction value does not have to be calculated for each of the channels 1 and 2. For example, the offset correction value of one channel is calculated and the offset correction is performed so that one channel is matched with the other channel. Anyway.

  In the second embodiment, the two-channel reading configuration has been described. Of course, the same processing can be performed in the case of multi-channel reading with three or more channels.

  In the second embodiment, the integral value calculation and the offset correction are performed for each channel. However, this may be performed for each color filter.

  As described above, according to the second embodiment, when a multi-channel readout image sensor is used, offset correction between channels can be performed quickly and accurately.

1 is a block diagram illustrating a schematic configuration of an imaging apparatus according to a first embodiment of the present invention. It is a flowchart which shows the imaging signal read-out control operation from the image pick-up element in embodiment of this invention. It is the figure which represented typically the pixel area | region of the image pick-up element in embodiment of this invention. 6 is a timing chart of reading an image signal from the image sensor according to the embodiment of the present invention. It is a block diagram which shows schematic structure of the imaging device in the 2nd Embodiment of this invention. It is a block diagram which shows schematic structure of the conventional digital camera. It is a flowchart which shows operation | movement of the conventional digital camera. It is a flowchart which shows the conventional imaging process operation. It is the figure which represented typically the image pick-up element of 2 channel read-out structure.

Explanation of symbols

101 Image sensor 102 A / D converter 103 DSP
104 Timing generation circuit 105 CPU
106 ROM
107 RAM
108 Recording medium 109 Power switch 110 Switch SW1
111 Switch SW2
112 Mode Dial 508 OB Unit Integration Circuit 509 Offset Correction Unit 510 Subtractor 511 RAM

Claims (8)

An imaging device that includes a first region that includes a plurality of pixels and from which a pixel signal that serves as a reference for offset correction is read, and a second region from which a pixel signal that is used as an image signal is read ;
Drive signal generating means for generating a drive signal for reading a pixel signal from the image sensor;
Calculating means for calculating an offset correction value based on the pixel signal of the first region;
And SL憶means you store the offset correction value,
Using the stored offset correction value, offset correction means for correcting a pixel signal read from the second region ;
It said drive signal generating means is controlled to stop the generation of the drive signal after the read end of the first region pixel signals, said calculation means an offset correction value based on the pixel signals of the first region read Calculating and controlling the calculated offset correction value to be stored in the storage unit, and after storing the offset correction value in the storage unit, the drive signal generation unit restarts the generation of the drive signal, imaging device and having a control Gosuru control means to read out pixel signals of the second region. The image pickup device have a plurality of read channels capable reads a plurality of pixel signals at the same time,
Said calculation means, for each of the plurality of read channels, claims, characterized and Turkey to calculate the offset correction value for correcting the offset difference between the plurality of read channels based on the pixel signals of the first region The imaging apparatus according to 1 .   The imaging apparatus according to claim 2, wherein the calculation unit calculates an offset correction value for each of the plurality of readout channels, and the offset correction unit corrects a pixel signal for each of the plurality of readout channels. . The imaging device is covered by a plurality of color filters,
Said calculation means, for each pixel signal corresponding to each color of the plurality of color filters, wherein the benzalkonium to calculate the offset correction value for correcting the offset difference between the respective colors based on the pixel signals of the first region The imaging apparatus according to claim 1.   The calculation means calculates an offset correction value for each color of the plurality of color filters, and the offset correction means has a plurality of correction means for correcting pixel signals for each color of the plurality of color filters. The imaging device according to claim 4. An image sensor comprising a plurality of pixels, a first area from which a pixel signal serving as a reference for offset correction is read, and a second area from which a pixel signal used as an image signal is read, and a pixel signal from the image sensor A control method for an imaging apparatus having drive signal generation means for generating a drive signal for reading,
A first readout step of reading out pixel signals of the first region;
A drive stop step in which the drive signal generation means stops generating the drive signal after the reading of the pixel signal of the first region is completed;
A calculation step of calculating the offset correction value based on the picture element signal of the first region,
And that SL憶process be stored in the storage means the offset correction value calculated in the calculating step,
After storage in the memory means of the offset correction value in the storage step, and a resume driving resumption step generation of said drive signal generating means said drive signal,
A second readout step of reading out the pixel signal of the second region;
An offset correction step of correcting a pixel signal read from the second area using the stored offset correction value. The image pickup device have a plurality of read channels capable reads a plurality of pixel signals at the same time,
In the first reading step, for each of the plurality of read channels, and read out the pixel signals of the first region,
Claims wherein in the calculating step, for each of the plurality of read channels, characterized by the Turkey to calculate the offset correction value for correcting the offset difference between the plurality of read channels based on the picture element signal of the first region Item 7. The control method according to Item 6 . The imaging device is covered by a plurality of color filters,
In the first reading step, for each pixel signal corresponding to each color of the plurality of color filters, and read out the pixel signals of the first region,
In the calculating step, for each pixel signal corresponding to each color of the plurality of color filters, and Turkey to calculate the offset correction value for correcting the offset difference between the first region of the image containing signal to each color based on The control method according to claim 6 .

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