JP2010141799A - Electronic camera, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electronic camera capable of suppressing image disturbance caused by a noise generated from a power supply circuit. <P>SOLUTION: The electronic camera includes an imaging element, a timing generator, a power supply circuit, a temperature detection part, a memory, an operation part, and a driving frequency control part. The imaging element photoelectrically converts an object image and outputs an image signal. The timing generator supplies a drive signal for driving the imaging element. The power supply circuit supplies power. The temperature detection part detects a temperature of the power supply circuit. The memory stores information indicating correspondence relation between a frequency of a noise generated due to the operation of the power supply circuit and a temperature. The operation part estimates the frequency of the noise on the basis of the detection result of the temperature detection part and the information indicating the correspondence relation. The driving frequency control part changes the driving frequency of the drive signal according to the noise frequency estimated by the operation part. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electronic camera and a program.

  Conventionally, in an electronic camera, noise processing or the like is performed on an image signal obtained from an image sensor (see, for example, Patent Document 1).

Patent Document 1 discloses a technique for preventing black crushing or black floating caused by dark current noise generated in an image sensor. Thereby, the electronic camera of patent document 1 can prevent that a white crack appears in an image.
JP 2004-120492 A

  Incidentally, in addition to dark current noise, noise generated from the power supply circuit of the electronic camera may adversely affect the image. That is, noise is generated in the power supply circuit due to the voltage control switching operation. This noise oscillation frequency (hereinafter referred to as “noise frequency”) includes the frequency of the n-th harmonic. When the frequency of the n-th harmonic is in the vicinity of a constant multiple of the drive frequency for driving the image sensor (corresponding to the readout frequency of the image signal of the image sensor), noise is superimposed on the output signal from the image sensor There is. When this noise is superimposed on the output signal, there arises a problem that the image is disturbed by a striped pattern or the like according to the signal level of the noise. There is a problem that the frequency of this noise differs for each power supply circuit due to variations in characteristics of components (capacitors, resistors, etc.) used in the power supply circuit in the manufacturing stage. In addition, there is a problem that the frequency of noise varies depending on the temperature of the power supply circuit. For this reason, the frequency of noise generated from the power supply circuit is not uniformly the same for each individual, and noise countermeasures are difficult.

  In view of the above circumstances, an object of the present invention is to provide an electronic camera that suppresses image disturbance caused by noise generated from a power supply circuit. It is another object of the present invention to provide a program that suppresses image disturbance caused by noise generated from a power supply circuit.

  An electronic camera according to a first invention includes an imaging device, a timing generator, a power supply circuit, a temperature detection unit, a memory, a calculation unit, and a drive frequency control unit. The image sensor photoelectrically converts the subject image and outputs an image signal. The timing generator supplies a drive signal for driving the image sensor. The power supply circuit supplies power. The temperature detection unit detects the temperature of the power supply circuit. The memory stores information indicating a correspondence relationship between the frequency of noise generated due to the operation of the power supply circuit and the temperature. The calculation unit estimates the noise frequency based on the detection result of the temperature detection unit and information indicating the correspondence. The drive frequency control unit changes the drive frequency of the drive signal according to the noise frequency estimated by the calculation unit.

  In a second aspect based on the first aspect, the drive frequency control section changes the drive frequency in units of an image signal line readout cycle or an image signal frame readout cycle.

  In a third aspect based on the first or second aspect, the drive frequency control unit inserts a waiting time within one cycle time of the drive frequency.

  In a fourth aspect based on the first or second aspect, the drive frequency control unit changes the clock frequency of the clock signal oscillator that outputs the clock signal to the timing generator.

  A program according to a fifth aspect causes the electronic camera according to any one of claims 1 to 4 to execute a temperature detection step, a calculation step, and a drive frequency control unit step. In the temperature detection step, the temperature of the power supply circuit that supplies power is detected. In the calculation step, the noise frequency is estimated based on information indicating a correspondence relationship between the frequency of the noise and the temperature generated along with the operation of the power supply circuit and the detection result of the temperature detection step. The drive frequency control unit step changes the drive frequency of the drive signal by issuing an instruction to a timing generator that supplies a drive signal for driving the image sensor in accordance with the noise frequency estimated by the calculation unit.

  According to the electronic camera of the present invention, it is possible to suppress image disturbance caused by noise generated from the power supply circuit.

(Description of the first embodiment)
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing the configuration of the electronic camera of this embodiment. As shown in FIG. 1, the electronic camera 1 includes a photographic lens 10, an image sensor 11, an A / D converter 12, a timing generator 13, a signal processor 14, a RAM (Random Access Memory) 15, and a flash. Memory 16, display control unit 17, liquid crystal display monitor 18, power supply circuit 19, temperature sensor 20, operation unit 21, CPU (Central processing Unit) 22, and recording interface (recording I / F) 23 A recording medium 24 and a bus 25 are provided. Among these, the signal processing unit 14, the RAM 15, the flash memory 16, the display control unit 17, the CPU 22, and the recording interface (recording I / F) 23 are connected to each other via a bus 25. The operation unit 21 is connected to the CPU 22.

  The photographing lens 10 includes a plurality of lens groups including a zoom lens and a focus lens. For the sake of simplicity, FIG. 1 shows the photographic lens 10 as a single lens.

  The image sensor 11 generates an image signal (analog signal) by photoelectrically converting incident light from the photographing lens 10. In the present embodiment, an XY address type CMOS (Complementary Metal-Oxide Semiconductor) is used for the image sensor 11.

  The A / D converter 12 converts an analog signal into a digital signal. The timing generator (TG) 13 supplies a drive signal to each of the image sensor 11 and the A / D converter 12 in accordance with an instruction from the CPU 22, thereby controlling the drive timing in synchronization with each other. Inside the timing generator (TG) 13, a pulse generator, a counter, and a crystal oscillator are provided. The counter counts the number of clocks of the crystal oscillator. The value of this counter is monitored by the CPU 22. When the value of the counter reaches a predetermined number of clocks, the drive frequency control unit 22c, which will be described later, issues an instruction to the timing generator (TG) 13 and outputs a drive signal (drive pulse) read from the pulse generator to the image sensor and the A / D. The data is supplied to the conversion unit 12.

  The signal processing unit 14 temporarily stores the image data of the digital signal output from the A / D conversion unit 12 in the RAM 15. Further, the signal processing unit 14 performs image processing such as white balance correction on the image data stored in the RAM 15.

  The flash memory 16 stores in advance information indicating the correspondence between the frequency of noise generated in accordance with the operation of the power supply circuit 19 and the temperature (details will be described later). The flash memory 16 also stores a program that is an embodiment of the present invention.

  The display control unit 17 displays the image data subjected to the image processing by the signal processing unit 14 on the liquid crystal display monitor 18 as an image.

  The power supply circuit 19 is a step-up / step-down switching power supply. The temperature sensor 20 detects the temperature (° C.) of the power supply circuit 19 and converts it into digital data. Here, the temperature sensor 20 detects the temperature of the substrate of the power supply circuit 19, and does not detect the temperature of the casing of the electronic camera 1. In order to further increase the accuracy of temperature detection, it is desirable that the temperature sensor 20 measures the temperature of the capacitor and resistance of the power supply circuit 19.

  The power supply circuit 19 periodically generates noise during the switching operation. The temperature characteristics of the noise frequency are measured in advance for each power supply circuit in the manufacturing stage. Here, as information indicating the correspondence relationship between the frequency of noise and temperature, the frequency information of noise that changes according to temperature and the information of the driving frequency for suppressing noise, which is determined based on the frequency information of the noise. It is. When the noise frequency changes with temperature, the frequency of the n-th harmonic changes. In this case, noise is suppressed if the n-fold harmonic and the drive frequency (readout frequency) have a constant multiple.

  FIG. 2 is a diagram for explaining the relationship between the drive frequency and the temperature characteristic of the noise frequency. FIG. 2A shows the passage of time when the image sensor 11 reads one line each time it receives a drive signal (drive pulse) from the timing generator (TG) 13. FIGS. 2B to 2E show temperature characteristics of noise frequency. An upwardly convex signal wave schematically represents the signal level of periodic noise.

  As an example, FIGS. 2B to 2E are temperature characteristics of noise frequencies at 25 ° C., 30 ° C., 40 ° C., and 50 ° C. in order. In the figure, black circles represent the signal level of noise at the sampling timing. By connecting these black circles with a line, the state of noise appearing in the image can be understood. When this line is a straight line, noise caused by the power supply circuit is not noticeable on the image. On the other hand, when this line becomes a broken line, noise caused by the power supply circuit becomes conspicuous on the image.

  Taking FIG. 2 as an example, if the frequency of the noise (frequency of the n-th harmonic) is at a constant multiple at 25 ° C., the noise is superimposed, but the noise signal level at the sampling timing Therefore, noise does not stand out on the image (FIG. 2B). In the case of FIG. 2C (30 ° C.), since the signal level of the noise at the sampling timing is almost uniform, the noise does not stand out on the image.

  However, when the temperature rises (40 ° C., 50 ° C.) and the noise frequency changes to a frequency close to a constant multiple of the drive frequency, the noise signal level at the sampling timing becomes uneven, and therefore noise appears on the image. Tends to stand out (for example, FIGS. 2D and 2E). Therefore, if the signal level of noise is made uniform for each temperature, the noise on the image becomes inconspicuous. That is, the drive frequency is changed in accordance with the temperature characteristics of the noise frequency so that the noise signal level is uniform (details will be described later).

  Information indicating the correspondence between the noise frequency and the temperature derived from FIG. 2 is written in the flash memory 16 at the time of factory shipment, for example.

  In FIG. 2, the cases of 25 ° C., 30 ° C., 40 ° C., and 50 ° C. are shown. That is, a driving frequency (information on a driving frequency that is a constant multiple of the noise frequency) for writing the noise signal level to the noise frequency at each temperature is written in the flash memory 16.

  The operation unit 21 is a release button, a command dial, or the like, and gives a signal to the CPU 22 in accordance with the content of operation by the user. For example, the user can give a shooting instruction to the CPU 22 by fully pressing the release button.

  The CPU 22 is a processor that performs overall control of the electronic camera 1. The CPU 22 calculates a parameter for each process and controls each part of the electronic camera 1 by executing a sequence program stored in advance in the flash memory 16. Further, the CPU 22 functions as a temperature detection unit 22a, a calculation unit 22b, and a drive frequency control unit 22c.

  The temperature detection unit 22a acquires data on the temperature detected by the temperature sensor 20.

  The calculation unit 22b estimates the noise frequency based on the temperature data that is the detection result of the temperature detection unit 22a and information indicating the correspondence between the noise frequency and the temperature stored in the flash memory 16. To do.

  The drive frequency control unit 22c changes the drive frequency of the drive signal according to the noise frequency estimated by the calculation unit 22b. In this case, the drive frequency control unit 22c changes the drive frequency by inserting a waiting time within one cycle time of the drive frequency (details will be described later). In the case of still image shooting, the drive frequency control unit 22c changes the drive frequency in units of one-line readout cycle of the image signal. For example, when the power supply circuit is changed from 25 ° C. to 30 ° C., the drive frequency control unit 22c changes the drive frequency associated with 25 ° C. to the drive frequency associated with 30 ° C. In this case, the timing generator (TG) 13 supplies a drive signal (drive pulse) to the image sensor 11 and the A / D converter 12 at a drive frequency associated with 30 ° C. The image sensor 11 and the A / D converter 12 sequentially read out the image signals in units of one-line reading cycle of the image signals in synchronization.

  The recording interface (recording I / F) 23 is formed with a connector for connecting the recording medium 24. The recording interface (recording I / F) 23 accesses the recording medium 24 connected to the connector according to an instruction from the CPU 22 and performs image recording processing.

  Next, an example of the operation of the electronic camera in the first embodiment will be described. In the following description, it is assumed that noise is superimposed on an image when the frequency of noise from the power supply circuit 19 is near a constant multiple of the readout frequency of the image sensor 11. Here, it is assumed that the drive frequency and the readout frequency are synchronized. When the power is turned on, it is assumed that it is operated at a driving frequency of 25 ° C. for convenience of explanation.

  In addition, the CPU 22 is configured with a temperature detection unit 22a, a calculation unit 22b, and a drive frequency control unit 22c by incorporating a program according to an embodiment of the present invention.

  FIG. 3 is a flowchart showing the operation of the electronic camera 1. This flowchart is started when the power of the electronic camera 1 is turned on.

  Step S <b> 101: First, the CPU 22 reads information indicating the correspondence relationship between the noise frequency and the temperature of the power supply circuit 19 from the flash memory 16. That is, information on the frequency of noise at each temperature and the driving frequency for aligning the noise signal level is read.

  Step S102: The CPU 22 determines whether or not a release has been performed. If the release is not performed (step S102: No), the process waits until the release is performed by repeating step S102. On the other hand, when the release has been performed (step S102: Yes), the process proceeds to step S103.

  Step S103: The temperature detector 22a of the CPU 22 reads temperature information from the temperature sensor 20.

  Step S104: The calculation unit 22b of the CPU 22 estimates the noise frequency of the power supply circuit 19 at the current temperature from the information obtained in Step S101 and Step S103. For example, for simplicity, it is assumed that at 25 ° C., the noise frequency is 0.1 MHz and the drive frequency is 1 MHz. In this case, the relationship between the tenth harmonic of the noise frequency (a harmonic of a constant multiple) and the drive frequency is a constant multiple.

  Step S105: The CPU 22 determines whether or not noise is likely to occur when the current drive frequency of the timing generator (TG) 13 is the noise frequency estimated in step S104.

  When there is no possibility that noise is generated (step S105: No), the processing routine proceeds to step S107. On the other hand, when there is a possibility that noise is generated (step S105: Yes), the processing routine proceeds to step S106. Here, in FIG. 2A, as described above, a state in which a drive signal (drive pulse) for one line reading is supplied to the image sensor 11 according to the drive frequency of the timing generator (TG) 13 is shown. Represents. FIG. 2A shows the driving frequency at 25 ° C. Therefore, when the temperature changes, there is a possibility that noise is generated at the driving frequency at 25 ° C. On the other hand, if the temperature is 25 ° C., there is no possibility that noise at a problematic level will occur.

  Step S106: The drive frequency control unit 22c of the CPU 22 changes the drive frequency by the method described below.

  FIG. 4 is a diagram schematically showing the change of the driving frequency. A state in which a drive signal (drive pulse) for one line reading is supplied to the image sensor 11 according to the drive frequency of the timing generator (TG) 13 is shown. FIG. 4A shows a state before the drive frequency is changed, and FIG. 4B shows a state after the drive frequency is changed.

  When the counter value of the timing generator (TG) 13 reaches the number of times corresponding to the drive frequency, the drive frequency control unit 22 c supplies a read drive signal for one line to the image sensor 11. When the drive frequency is changed, after the counter value of the timing generator (TG) 13 reaches the number of times corresponding to the drive frequency, the drive frequency control unit 22c is driven by stopping the count of the clock frequency for a predetermined time. The supply of the signal is temporarily stopped, and the supply of the drive signal is resumed after a predetermined time has elapsed. Thereafter, the same processing is repeated. In this embodiment, this process is set as waiting time insertion. As a result, the drive frequency is changed. In this way, by performing the process of inserting the waiting time a plurality of times, the timing for reading out the image signal can be shifted, and the image signal can be read out at the timing when the noise signal levels are uniform. Note that the timing of inserting the waiting time is an example, and is not limited to the above method.

  Here, for simplicity, the case where the temperature of the power supply circuit 19 is changed from 25 ° C. to 50 ° C. will be described.

  FIG. 5 is a diagram illustrating the relationship between the drive frequency and the temperature characteristic of the noise frequency. FIG. 5A to FIG. 5D utilize FIG. Here, FIG. 5 (f) shows that when the power supply circuit 19 is 50 ° C., the driving signal (driving pulse) for one line reading is set to the driving frequency of the timing generator (TG) 13 with respect to the image sensor 11. It shows how it is supplied accordingly. The drive frequency control unit 22c changes the drive frequency shown in FIG. 5A to the drive frequency shown in FIG. Therefore, the drive frequency control unit 22c changes the drive frequency at 25 ° C. to the drive frequency at 50 ° C. in units of one-line readout cycle of the image signal.

  In this way, in the case of the driving frequency shown in FIG. 5 (f), the noise signal level at the sampling time in FIG. 5 (e) becomes uniform, and image disturbance occurs when the noise signal levels are uneven. Is suppressed. Further, when the temperature of the power supply circuit is lowered from 50 ° C. to 25 ° C., the insertion of the waiting time is stopped and the drive frequency shown in FIG.

  The change of the driving frequency is not limited to the above method, and the clock frequency of the clock signal oscillator that outputs the clock signal to the timing generator (TG) 13 may be changed. In this way, it is not necessary to perform processing for inserting waiting time.

  Step S107: The CPU 22 instructs the signal processing unit 14 to acquire an image. The signal processing unit 14 temporarily stores the image data of the digital signal output from the A / D conversion unit 12 in the RAM 15. Further, the signal processing unit 14 performs image processing such as white balance correction on the image data stored in the RAM 15. The CPU 22 records the image data subjected to the image processing on the recording medium 24 via the recording interface (recording I / F) 23. Then, this processing routine ends.

  In the present embodiment, the drive frequency is changed after reading out every line. However, at the time of moving image shooting, the drive frequency may be changed after reading out one frame.

  As for the waiting time insertion, it is desirable that the increase in one cycle time is within about 10% in consideration of the readout time of the image signal.

  As described above, according to the electronic camera 1 of the present embodiment, the calculation unit 22b estimates the noise frequency based on the detection result of the temperature detection unit 22a and the information indicating the correspondence relationship. The drive frequency control unit 22c changes the drive frequency of the drive signal according to the noise frequency estimated by the calculation unit 22b. Thereby, the electronic camera 1 can suppress image distortion caused by noise generated from the power supply circuit 19.

The block diagram which shows the structure of the electronic camera of this embodiment The figure explaining the relationship between the drive frequency and the temperature characteristics of the noise frequency A flowchart showing the operation of the electronic camera 1 Diagram showing changes in drive frequency The figure explaining the relationship between the drive frequency and the temperature characteristics of the noise frequency

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electronic camera, 11 ... Image sensor, 13 ... Timing generator, 22a ... Temperature detection part, 22b ... Calculation part, 22c ... Drive frequency control part, 19 ... Power supply circuit

Claims (5)

An image sensor that photoelectrically converts a subject image and outputs an image signal;
A timing generator for supplying a drive signal for driving the image sensor;
A power supply circuit for supplying power;
A temperature detector for detecting the temperature of the power supply circuit;
A memory for storing information indicating a correspondence relationship between a frequency of noise generated in association with an operation of the power supply circuit and the temperature;
Based on the detection result of the temperature detection unit and information indicating the correspondence relationship, a calculation unit that estimates the frequency of the noise,
A drive frequency control unit that changes the drive frequency of the drive signal according to the frequency of the noise estimated by the calculation unit;
An electronic camera characterized by comprising: The electronic camera according to claim 1,
The drive frequency control unit changes the drive frequency in units of a line readout cycle of the image signal or a frame readout cycle of the image signal. The electronic camera according to claim 1 or 2,
The electronic camera according to claim 1, wherein the driving frequency control unit inserts a waiting time within one cycle time of the driving frequency. The electronic camera according to claim 1 or 2,
The electronic camera characterized in that the drive frequency control unit changes a clock frequency of a clock signal oscillator that outputs a clock signal to the timing generator. The electronic camera according to any one of claims 1 to 4,
A temperature detection step for detecting the temperature of the power supply circuit for supplying power;
A calculation step for estimating the frequency of the noise based on information indicating a correspondence relationship between the frequency of the noise generated in association with the operation of the power supply circuit and the temperature, and a detection result of the temperature detection step;
A drive frequency control unit step of changing the drive frequency of the drive signal by giving an instruction to a timing generator that supplies a drive signal for driving the image sensor according to the frequency of the noise estimated by the arithmetic unit; A program for running

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