JP2010016631A - Imaging apparatus - Google Patents

Abstract

[PROBLEMS] To prevent an increase in power consumption when an image is displayed in live view.
An imaging device captures an image of a subject and outputs a pixel signal. The imaging device includes a plurality of pixels arranged in a matrix, and the pixels included in a predetermined row among the plurality of pixels. First reading means 144 for reading the first pixel signal, second reading means 144 for reading a second pixel signal for generating either a display image or a recording image from the plurality of pixels 141, a first A calculation unit 181 for calculating a correction value for correcting an error for each pixel column of the second pixel signal using the pixel signal, and a correction for correcting the second pixel signal using the calculated correction value Means 181 and control means 18 that prohibits the correction means 181 from correcting the second pixel signal when a predetermined condition is satisfied in the live view mode in which an image is displayed without recording on a recording medium. The Obtain.
[Selection] Figure 2

Description

  The present invention relates to an imaging apparatus that corrects noise included in a pixel signal from an imaging element.

2. Description of the Related Art Conventionally, a camera that corrects fixed pattern noise (FPN) caused by an XY address type solid-state imaging device is known (for example, Patent Document 1).
JP 10-1226697 A

  However, when FPN correction processing is performed on an image displayed in live view, there is a problem that power consumption increases.

  An image pickup apparatus according to a first aspect of the invention picks up a subject image and outputs a pixel signal, an image pickup element in which a plurality of pixels are arranged in a matrix, and a pixel included in a predetermined row among the plurality of pixels First reading means for reading out the first pixel signal from the second reading means, second reading means for reading out the second pixel signal for generating either the display image or the recording image from the plurality of pixels, and the first pixel signal. A correction means for calculating a correction value for correcting an error for each pixel column of the second pixel signal, a correction means for correcting the second pixel signal using the calculated correction value, And a control unit that prohibits the correction unit from correcting the second pixel signal when a predetermined condition is satisfied in a live view mode in which an image is displayed without recording on a recording medium. To do.

  According to the present invention, when the predetermined condition is satisfied, the correction unit can be prohibited from correcting the second pixel signal.

-First embodiment-
A camera according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a main configuration of the electronic camera 1. An interchangeable lens 2 including a photographing lens L1 and a diaphragm 20 is detachably attached to the body of the electronic camera 1. On the body side of the camera 1, a quick return mirror 10, a focusing screen 11, a pentaprism 12, an eyepiece lens 13, an image sensor 14, and a focus detection sensor 15 are provided.

  FIG. 2 is a block diagram of the control system of the electronic camera 1. In FIG. 2, the components shown in FIG. The control system of the electronic camera 1 includes an image sensor 14, an A / D conversion circuit 16, a timing generator 17, a control circuit 18, an LCD drive circuit 19, a liquid crystal display 191, an operation unit 30, a memory card interface 31, a battery 40, and a battery. A voltage detection circuit 41 is provided.

  Referring to FIG. 1, the subject light that has passed through the interchangeable lens 2 and entered the electronic camera 1 is guided upward by a quick return mirror 10 positioned as indicated by a solid line in FIG. 1 before the shutter release. An image is formed on the focusing screen 11. The subject image formed on the focusing screen 11 is guided to the eyepiece 13 by the pentaprism 12. As a result, the subject image is observed by the photographer. Part of the subject light passes through the semi-transmission region of the quick return mirror 10, is reflected downward by the sub mirror 10 a, and enters the focus detection sensor 15. After the release, the quick return mirror 10 is rotated to the position indicated by the broken line in FIG. 1, the subject light is guided to the imaging device 14, and the subject image is formed on the imaging surface.

The control system will be described in detail with reference to FIG.
The image sensor 14 includes a plurality of pixel photodiodes 141 arranged in a matrix, a switch 142 provided in each of the pixel photodiodes 141, a vertical scanning circuit 143 for sequentially selecting each row of the pixel photodiodes 141, and column processing. An X-Y address photoelectric conversion element including a circuit 144 is provided. The switch 142 includes a transfer gate switch 142A (hereinafter referred to as switch 142A), a pixel selection switch 142B (hereinafter referred to as switch 142B), and a capacitor 142C.

  The switch 142A is a switch that is provided between the pixel photodiode 141 and the capacitor 142C and switches ON / OFF of the electrical connection between the pixel photodiode 141 and the capacitor 142C. The capacitor 142C is provided to convert the charge photoelectrically converted by the pixel photodiode 141 into a voltage value. The switch 142B is a switch that is provided between the capacitor 142C and the column processing circuit 144 and switches ON / OFF of the electrical connection between the capacitor 142C and the column processing circuit 144. When the switches 142A and 142B of a certain pixel are both turned on, the signal received by the pixel is photoelectrically converted and transmitted to the column processing circuit 144.

  On the other hand, when the switch 142A of a certain pixel is turned off and the switch 142B is turned on, a signal when the connection between the pixel photodiode 141 and the column processing circuit 144 is cut off, that is, the pixel receives light. A signal equivalent to a signal in a state in which it is not (an element of FPN described later) is transmitted to the column processing circuit 144. The pixel photodiode 141 converts the received subject light into a pixel signal corresponding to the intensity thereof, and outputs the pixel signal to the A / D conversion circuit 16 via the switch 142 (switch 142A, switch 142B) and the column signal circuit 144.

  The column processing circuit 144 includes a CDS circuit, a line memory, and the like for each column of the pixel photodiode 141, and the pixel photodiode 141 in a predetermined row selected by the vertical scanning circuit 143 (the switch 142A for each pixel in the selected row is turned off). And the switch 142B is turned on). In this case, at least the switches 142B of the pixel photodiodes 141 included in the unselected rows are all turned off.

  The column processing circuit 144 holds a pixel signal obtained when the switch 142A for each pixel in the selected row is off and the switch 142B is on as an offset signal for each column. At this time, the switches 142A and 142B are turned on and off almost simultaneously between the selected pixels. The offset signal obtained in this manner is a streak-like fixed pattern noise (hereinafter referred to as FPN) generated in the vertical direction of the captured image due to a column processing circuit 144 described later, that is, the image sensor 14. Fixed pattern noise (FPN) for each column.

  The control circuit 18 described later calculates a correction value (FPN correction value) using the obtained FPN, and performs FPN correction on the image signal using the calculated FPN correction value. The calculated FPN correction value is stored in a temporary memory 183 provided in an image processing unit 181 described later.

  When obtaining the FPN, as described above, the pixel photodiodes 141 in a predetermined row (selected row) are turned off all at once (the pixel switches 142A in the selected row are turned on all at once, and the switches 142B are turned on all at once. In addition to the method of obtaining the pixel signal, the following method may be used. For example, the FPN may be obtained in a state in which the switches 142A of all rows of pixels (that is, all pixels) are turned off all at once and only the pixel switches 142B of a predetermined row (selected row) are turned on all at once.

  The A / D conversion circuit 16 is a circuit that performs analog processing on the pixel signal output from the image sensor 14 and then converts it to digital image data. The timing generator 17 outputs a timing signal to the image sensor 14 and the A / D converter circuit 16 in accordance with a command from the control circuit 18 and controls the drive timing of the image sensor 14 and the A / D converter circuit 16. It is.

  The control circuit 18 includes a CPU, ROM, RAM, and the like (not shown), and is an arithmetic circuit that controls each component of the electronic camera 1 and executes various data processing. The control circuit 18 controls the timing generator 17 described above.

  The control circuit 18 includes an image processing unit 181 and a compression unit 182. The image processing unit 181 performs image processing such as white balance processing, gamma correction processing, color interpolation processing, contour enhancement, and vignette correction on the input image data. The compression unit 182 is a circuit that performs JPEG compression processing on image data generated by image processing performed by the image processing unit 181.

  The memory card interface 31 is an interface to which the memory card 32 can be attached and detached. The memory card interface 31 writes image data to the memory card 32 or reads image data recorded on the memory card 32 based on the control of the control circuit 18. The memory card 32 is a semiconductor memory card such as a compact flash (registered trademark) or an SD card.

  The battery voltage detection circuit 41 constantly measures the remaining power capacity of the battery 40. The remaining capacity signal as the measurement result is output to the control circuit 18 via an A / D conversion circuit (not shown). Based on the input remaining capacity signal, the control circuit 18 compares the remaining capacity of the battery 40 with a preset threshold value (for example, 50% of the total capacity) and, as will be described later, the FPN correction value in the live view mode. It is determined whether or not the correction signal for calculating the FPN correction processing and the FPN correction processing for the main image signal are necessary.

  The LCD drive circuit 19 is a circuit that drives the liquid crystal display 191 based on a command from the control circuit 18. The liquid crystal display 191 displays the display data created by the control circuit 18 based on the image data recorded on the memory card 32 in the reproduction mode. The liquid crystal display 191 is configured to display a so-called live view image. The live view is a display mode in which the quick return mirror 10 is flipped upward before the release and an image captured by the image sensor 14 is displayed on the liquid crystal display 191 in real time. The live view is an imaging mode employed in a single-lens reflex camera. is there.

  The operation unit 30 is a switch that receives a user operation. The operation unit 30 includes a power switch, a release switch, other setting menu display changeover switches, a setting menu determination button, and the like. The operation unit 30 can set a still image shooting mode as a shooting mode and a live view mode for displaying the above live view image. Therefore, when the still image shooting mode and the live view mode are set, when the user fully presses the release switch while the live view image is displayed, the process shifts to still image shooting.

-Still image shooting mode-
When the still image shooting mode is set by operating the operation unit 30 and shooting is instructed by pressing the release switch fully, the control circuit 18 rotates the quick return mirror 10 to the position indicated by the broken line in FIG. The subject light that has passed through the photographing lens L1 is guided to the image sensor 14. Further, the control circuit 18 instructs the timing generator 17 to output from the pixel photodiode 141 corresponding to, for example, a pixel corresponding to a region of 1/3 of the range of all pixels constituting the image sensor 14. Then, the switch 142 is turned on via the vertical scanning circuit 143.

  FIG. 3 shows a pixel area from which a correction signal (FPN) used for calculation of the FPN correction value is read out by a hatched area. In order to simplify the description, it is assumed that the number of pixels of the image sensor 14 is 3000 × 1500 pixels. In the present embodiment, for example, pixel signals output from the pixels (3000 × 500 pixels) corresponding to the upper third region of the entire pixel range are read for 3000 columns. That is, the vertical scanning circuit 143 selects the first row to the 500th row as the selected row, turns off the switch 142A for each pixel included in the selected row, and turns on the switch 142B. Note that selected rows may be set every predetermined row (for example, every three rows). As a result, pixel signals (FPN) are read from the 500 pixel photodiodes 141 for each of the first to 3000th columns of the image sensor 14 and input to the column processing circuit 144.

  The column processing circuit 144 outputs pixel signals for all columns, that is, 3000 columns, to the image processing unit 181 of the control circuit 18 via the A / D conversion circuit 16. The image processing unit 181 calculates the FPN correction value by averaging the pixel signals (500 pixels) for each of the 3000 columns input as described above, and stores them in the temporary memory 183.

  Next, the control circuit 18 instructs the timing generator 17 to turn on both the switches 142A and 142B of all the pixels, and the pixel signals output from all the pixels of the image sensor 14 are used for the main image for still image shooting. The signal is input to the image processing unit 181 as a signal. The image processing unit 181 subtracts the corresponding first row FPN correction value from the input first row main image signal. The image processing unit 181 performs the FPN correction process by performing the above subtraction on the respective pixel signals for 3000 columns. The pixel signal that has been subjected to the FPN correction process is subjected to the above-described image processing and compression processing by the control circuit 18, and is recorded in the memory card 32 as still image data. Note that the FPN correction processing in the case of shifting from still-view image display to still image shooting will be described later.

-Live view mode-
When the live view mode is set by operating the operation unit 30, the control circuit 18 rotates the quick return mirror 10 to a position indicated by a broken line in FIG. 1, and subject light that has passed through the photographing lens L 1 is applied to the image sensor 14. To be guided. As shown in FIG. 4A, in the live view mode, the control circuit 18 is a pixel photodiode 141 that is thinned out to 1/3 (500 rows) in the vertical direction among all the pixels constituting the image sensor 14. The image data for the main image is generated using the main image signal (one frame image of the live view image) read out from. Note that the pixel signal is read at a period of 1/30 seconds, for example. Details will be described below.

  When the control circuit 18 detects that the remaining capacity of the battery 40 is equal to or greater than a threshold value (for example, 50% of the total capacity) in the live view mode, the FPN correction value is read before reading the main image signal. A selected row for reading a correction signal used for calculation is determined. When 500 rows are used for reading out the main image signal, the control circuit 18 instructs the timing generator 17 to further reduce the pixel photodiodes in the 500/3 row (166 rows) in the vertical direction, for example, by 1/3. The switch 142A is turned off and the switch 142B is turned on via the vertical scanning circuit 143 so that the correction signal is output from the 141.

  FIG. 4B shows pixels read out by thinning out in order to obtain a correction signal in the live view mode. In this case, the pixel from which the pixel signal is read is indicated by a hatched area. That is, the vertical scanning circuit 143 selects the first to 166th rows as the selected row, turns off the switch 142A of the pixels included in the selected row, and turns on the switch 142B. Note that selected rows may be set every predetermined row (for example, every three rows). As a result, correction signals are read from a total of 166 pixel photodiodes 141 for each column of the image sensor 14 and input to the column processing circuit 144. The column processing circuit 144 outputs 166 correction signals for each of these columns to the control circuit 18 via the A / D conversion circuit 16.

  The control circuit 18 calculates the FPN correction value 1 for each column by averaging the pixel signals for each of the 3000 columns input as described above, and stores them in the temporary memory 183.

  When acquiring the image of the first frame for live view, the control circuit 18 instructs the timing generator 17 as shown in FIG. 4A to use the main image from the pixel photodiodes 141 in 500 rows. The switch 142A and the switch 142B are turned on through the vertical scanning circuit 143 so that a signal is output. That is, for example, the vertical scanning circuit 143 turns on the switches 142A and 142B with the second row, the fifth row,..., The (3n−1) th row (n is a natural number: n ≦ 500) as the selected row. . Then, the main image signal is output to the image processing unit 181 of the control circuit 18, and the FPN correction value 1 corresponding to the first column is subtracted from the main image signal in the first column. The image processing unit 181 performs the FPN correction process by performing the above subtraction on the respective main image signals for 3000 columns.

  Even in the case of acquiring the second frame image for live view, the control circuit 18 first reads out correction signals from a total of 166 pixel photodiodes 141 for each column of the image sensor 14, and the column processing circuit 144. To input. The column processing circuit 144 outputs 166 correction signals for each of these columns to the control circuit 18 via the A / D conversion circuit 16.

As in the case of the first frame, the control circuit 181 calculates the FPN correction value 2 for each column by averaging the correction signals for every 3000 columns. The image processing unit 181 reads the FPN correction value 1 stored in the temporary memory 183, averages the calculated FPN correction value 2 and the read FPN correction value 1, and sets the FPN correction value 2 _AVE for each column. Calculate and store in the temporary memory 183. Thereafter, as in the case of the first frame, the main image signal for the second frame of the live view is read, and the FPN correction value 2 _AVE of the corresponding column is subtracted from the main image signal for 3000 columns. FPN correction is performed.

While the image is acquired in the live view mode, the image processing unit 181 calculates the FPN correction value as described above. That is, when the image of the Nth frame is acquired, the FPN correction value (N−1) _AVE calculated when the image of the previous (N−1) th frame is acquired is read out and The FPN correction value N _AVE is calculated for each column using the equation (1).
FPN correction value N _AVE = {FPN correction value (N−1) _AVE + FPN correction value N} / 2 (1)

The image processing unit 181 performs FPN correction processing by subtracting the calculated FPN correction value _NAVE from the main image signal. Then, the image processing unit 181 performs the above-described image processing on the main image signal after the FPN correction processing to generate image data, and the control circuit 18 displays an image corresponding to the image data on the liquid crystal display 191. To do. While the correction signal for the Nth frame is being read, the control circuit 18 displays the (N−1) th frame image on the liquid crystal display 191.

On the other hand, after acquiring the image of the Nth frame as described above, when detecting that the remaining capacity of the battery 40 is less than 50% of the total capacity which is the threshold, the control circuit 18 reads the correction signal and FPN correction processing is prohibited. That is, the control circuit 18 instructs the timing generator 17 to read out only the main image signal for the image after the (N + 1) th frame. Further, the image processing unit 181, with respect to the (N + 1) th frame after the main image signal inputted, not subjected to FPN correction processing using the FPN correction value _{N AVE} described above.

-Transition from Live View image display to still image shooting-
In the live view mode described above, when the control circuit 18 inputs a shooting instruction signal by fully pressing the release switch, the control circuit 18 instructs the timing generator 17 to turn on all the switches 142A and 142B. Then, pixel signals output from all the pixels of the image sensor 14 are input to the image processing unit 181 as main image signals for still image shooting. The image processing unit 181 reads the FPN correction value N _AVE stored in the temporary memory 183 and subtracts the FPN correction value N _AVE of the corresponding column from the input main image signal. That is, the image processing unit 181, by using the FPN correction value N _AVE acquired last before recording starts, it performs FPN correction processing on the image signals that have been input.

According to the electronic camera 1 of the first embodiment described above, the following operational effects can be obtained.
When the control circuit 18 detects that the remaining capacity of the battery 40 is less than the threshold (50% of the total capacity) when the live view mode is set, the control circuit 18 prohibits reading of the correction signal and FPN correction processing. I did it. Therefore, when the remaining capacity of the battery 40 decreases, the driving time of the image sensor 14 can be reduced and the processing load required for FPN correction can be reduced, which contributes to power saving.

-Second Embodiment-
A camera according to a second embodiment of the present invention will be described with reference to FIG. In the following description, the same components as those in the first embodiment are denoted by the same reference numerals, and different points will be mainly described. Points that are not particularly described are the same as those in the first embodiment. In the present embodiment, in place of the remaining capacity of the battery 40, when the temperature in the vicinity of the image sensor 14 becomes a predetermined value or higher during live view image display, reading of the correction signal and FPN correction processing are prohibited. This is different from the embodiment.

  As shown in FIG. 5, the electronic camera 1 includes a temperature sensor 42. The temperature sensor 42 constantly measures the temperature around the image sensor 14 and outputs a temperature signal as a measurement result to the control circuit 18 via an A / D conversion circuit (not shown). Based on the input temperature signal, the control circuit 18 compares the temperature in the vicinity of the image sensor 14 measured by the temperature sensor 42 with a preset threshold value (for example, 45 ° C.). The threshold value is a value determined depending on the rating of the image sensor 14. In the case of a camera having a function of terminating the live view mode when the temperature in the vicinity of the image sensor 14 is equal to or higher than a predetermined value, the threshold value is set to a value lower than the predetermined value.

  When the control circuit 18 detects that the temperature in the vicinity of the image sensor 14 measured by the temperature sensor 42 is less than the threshold (45 ° C.) in the live view mode, the control circuit 18 selects the main image signal and the correction signal. Determine the line. That is, the control circuit 18 reads out the main image signal by thinning it out to 1/3 (500 rows) in the vertical direction among all the pixels of the image sensor 14, and reads 500/3 rows (166) of all the pixels of the image sensor 14. The correction signal is read out using (line) as the selected line.

The control circuit 18 detects that the temperature in the vicinity of the image sensor 14 measured by the temperature sensor 42 is equal to or higher than a threshold (45 ° C.) after the N-th frame main image signal is acquired in the live view mode. In such a case, the timing generator 17 is instructed to prohibit reading of the correction signal. Further, the image processing unit 181 does not perform the FPN correction process using the FPN correction value N _AVE for the main image signal after the (N + 1) th frame.

According to the electronic camera 1 of the second embodiment described above, the following operational effects can be obtained.
When the control circuit 18 detects that the temperature in the vicinity of the image sensor 14 is equal to or higher than a threshold (45 ° C.) when the live view mode is set, the control circuit 18 prohibits reading of the correction signal and FPN correction processing. did. Therefore, when the temperature in the vicinity of the image sensor 14 rises, the drive time of the image sensor 14 is decreased to suppress the temperature rise, and the processing load required for FPN correction can be reduced, which contributes to power saving. .

The camera according to the embodiment described above can be modified as follows.
(1) When the electronic camera 1 includes the temperature sensor 42, the control circuit 18 corrects when the temperature in the vicinity of the image sensor 14 detected by the temperature sensor 42 is equal to or higher than the threshold or when the remaining capacity of the battery 40 is lower than the threshold. The acquisition of the image signal and the FPN correction processing for the image signal may be prohibited.
(2) The electronic camera 1 may be a photographic lens fixed type camera instead of a photographic lens exchangeable one.

  In addition, the present invention is not limited to the above-described embodiment as long as the characteristics of the present invention are not impaired, and other forms conceivable within the scope of the technical idea of the present invention are also within the scope of the present invention. included.

The figure which shows the principal part structure of the electric potential camera by embodiment of this invention. The block diagram which shows the structure of the control system of the electronic camera in 1st Embodiment The figure which shows an example of the area | region of the pixel from which a pixel signal is read in still image shooting mode The figure which shows an example of the area | region of the pixel from which a pixel signal is read in live view mode The block diagram which shows the structure of the control system of the electronic camera in 2nd Embodiment

Explanation of symbols

DESCRIPTION OF SYMBOLS 14 ... Imaging device 18 ... Control circuit 40 ... Battery 41 ... Battery voltage detection circuit 42 ... Temperature sensor 141 ... Pixel photodiode 144 ... Column processing circuit 181 ... Image Processing part

Claims (4)

An image sensor that captures a subject image and outputs a pixel signal, and a plurality of pixels arranged in a matrix;
First reading means for reading a first pixel signal from pixels included in a predetermined row among the plurality of pixels;
Second reading means for reading from the plurality of pixels a second pixel signal for generating either a display image or a recording image;
Calculating means for calculating a correction value for correcting an error for each pixel column of the second pixel signal using the first pixel signal;
Correction means for correcting the second pixel signal using the calculated correction value;
A control unit that prohibits the correction unit from correcting the second pixel signal when a predetermined condition is satisfied in a live view mode in which an image is displayed without recording on a recording medium. An imaging device that is characterized. The imaging device according to claim 1,
It further comprises capacity detection means for detecting the remaining capacity of the battery,
The imaging apparatus, wherein the predetermined condition for prohibiting the correction to the second pixel signal is that the detected remaining battery capacity is less than a predetermined threshold value. The imaging device according to claim 1,
Temperature detecting means for detecting the temperature in the vicinity of the image sensor;
An imaging apparatus characterized in that, as the predetermined condition for prohibiting correction to the second pixel signal, the detected temperature is equal to or higher than a predetermined threshold value. In the imaging device according to any one of claims 1 to 3,
The image pickup apparatus, wherein the control unit prohibits the first reading unit from reading the first pixel signal when the predetermined condition is satisfied.

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