JP2007329604A - Fluorescent light flicker detection circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of detecting a fluorescent light flicker caused in an image when a camera apparatus installed with a CMOS sensor adopting the XY address system photographs the image under fluorescent light illumination without using a light receiving element or the like independently of a relationship between a field period of the image and a luminance change period of a fluorescent light. <P>SOLUTION: A fluorescent light flicker detection circuit detects the presence/absence of the fluorescent light flicker from two fields adjacent to each other, changes an electronic shutter speed depending on a result of the detection, and compares fields before and after the change in the electronic shutter speed so as to discriminate the photographing environment. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The technical field relates to a technique for detecting fluorescent flicker that occurs in an image when imaged under non-inverter fluorescent lamp illumination using a camera device equipped with an image sensor.

  When fluorescent lamp flicker occurs, the image quality is significantly deteriorated. Therefore, it is necessary to reduce the flicker, and it is necessary to detect the fluorescent lamp flicker first. Accordingly, a method for detecting fluorescent lamp flicker in an image has been proposed.

  Patent Documents 1 and 2 disclose a method of estimating a flicker component by providing a light receiving element and a photometric element and measuring the light quantity of a fluorescent lamp.

  Patent Document 3 states that “the method of estimating the flicker component by measuring the light quantity of a fluorescent lamp using a light receiving element or a photometric element adds a light receiving element or a photometric element to the imaging apparatus. Therefore, the present invention eliminates the flicker inherent in the XY address scanning type image pickup device such as a CMOS image pickup device by using simple signal processing without using a light receiving device or the like, and a subject or video signal. Regardless of the level and type of fluorescent lamp, etc., it is possible to detect with high accuracy and reliably and sufficiently reduce the input image as the video signal or the luminance signal as an input image signal. The process of integrating the signal over a period of one horizontal period and the difference between the integrated value or the integrated value in the adjacent field or frame And there is a description of a step of normalizing comprises the steps of extracting the spectrum of the integral value or the difference value after the normalization, and ... "estimates the flicker component from the spectrum that extracted.

JP 2000-350102 A JP 2000-23040 A JP 2004-222228 A

  However, the methods of separately providing a light receiving element, a photometric element, and the like as in Patent Documents 1 and 2 have a problem that the cost and size of the photographing apparatus increase.

  Patent Document 3 also has a problem. The problem will be described using 4 to 6 together with the cause of flicker.

  When taking a picture under fluorescent lighting using a camera device equipped with, for example, an XY address type CMOS (Complementary Metal Oxide Semiconductor) sensor as the image sensor, image quality degradation appears to have horizontal stripes on the screen called fluorescent light flicker. Produce. The cause of the fluorescent lamp flicker will be described with reference to FIGS.

  Unlike the CCD (Charge Coupled Devices) sensor, the CMOS sensor employs a technique called “rolling shutter” in which the exposure start and exposure end (charge transfer) of the photodiode are sequentially performed for each of a plurality of lines in one field (screen). Therefore, the exposure start timing and the exposure end timing are different for each line even within one field.

  In the upper diagram of FIG. 4, the horizontal axis represents time and the vertical axis represents luminance, and the period of change in luminance of the fluorescent lamp is 1/100 second (the period of change in luminance of the fluorescent lamp is determined by the power supply frequency of the fluorescent lamp. FIG. 5 is a diagram depicting a change in luminance of a fluorescent lamp with a power cycle of the fluorescent lamp being 1/50 seconds) and a field period of 1/60 seconds (in the case of NTSC = National Television Standards Committee system). The right diagram of FIG. 4 is a diagram in which the horizontal axis represents luminance and the vertical axis represents a line, and changes in luminance with respect to the line are drawn for each field.

  As shown in the right diagram of FIG. 4, the luminance changes with respect to the line, and when viewed on the screen (field), it appears that the screen has bright and dark horizontal stripes. This is fluorescent lamp flicker. Also, since the phase of the luminance change is shifted for each field, the horizontal stripes on the screen due to flicker move up and down and appear to wave.

  On the other hand, FIG. 5 shows the luminance change of the photographed image when the field period is 1/60 seconds and the luminance change period of the fluorescent lamp is 1/120 seconds (the power supply period of the fluorescent lamp is 1/60 seconds). When the field period of the photographed image is an integral multiple of the luminance change period of the fluorescent lamp or 1 / multiple of an integral number (hereinafter also referred to as an integer multiple), there is no difference in the exposure amount for each line. As shown in the right figure, the luminance is constant between lines and fields, and no fluorescent lamp flicker occurs.

  In Patent Document 3, a difference between adjacent fields or frames is used. When the field period of the image is an integer multiple of the luminance change period of the fluorescent lamp as shown in FIG. 5, there is no difference between the fields, and the field period of the image is an integer of the luminance change period of the fluorescent lamp as shown in FIG. If it is neither a multiple nor a fraction of an integer (hereinafter also referred to as a non-integer multiple), the generated flicker pattern differs between fields, so that the difference value has a correlation with the flicker component and may detect flicker. Absent.

  However, the camera has a function of adjusting the exposure amount by changing the exposure time called “electronic shutter”.

  Here, as shown in FIG. 6, the field period of the image is an integral multiple (1/120 seconds) of the luminance change period of the fluorescent lamp, and the exposure time by the electronic shutter is a non-integer multiple of the luminance change period of the fluorescent lamp. In the case of (1/100 second), a difference in luminance occurs between the lines as shown in the right diagram of FIG. 6, so that horizontal stripe fluorescent lamp flicker occurs, but the exposure timing and the phase of the luminance change of the fluorescent lamp are always constant. Since it is constant, there is no difference in luminance between fields. The horizontal stripes appear to be fixed on the screen.

  In the case of FIG. 6, the generated flicker pattern is the same between fields, so the difference value has no correlation with the flicker component. Therefore, the technique of Patent Document 3 has a problem that flicker cannot be detected because it cannot be determined from the difference value whether flicker has occurred or not.

  Therefore, for example, if a camera device equipped with an XY address type CMOS sensor is used for photographing under fluorescent lamp illumination, fluorescent light flicker generated in an image can be detected without using a light receiving element or the like. Provided is a technique for detecting regardless of the relationship between the period and the luminance change period of the fluorescent lamp.

  Specifically, for example, a method for detecting flicker by fluorescent lamps of the first and second luminance periods, and when there is a difference in exposure amount between fields depending on the first exposure period of the image sensor, the first When it is determined that there is no difference between the flickers of the fluorescent lamps of the seed luminance cycle and there is no difference, the exposure period of the image sensor is changed, and when there is a phase shift in the exposure brightness before and after the change of the exposure period, It is determined that the flicker is caused by a fluorescent lamp with a period.

  For example, according to the above means, it is possible to detect fluorescent lamp flicker even if the exposure time by the electronic shutter is a non-integer multiple of the luminance change period of the fluorescent lamp.

  Problems, means, and effects other than those described above will be clarified by examples described later.

  Hereinafter, an example of a fluorescent lamp flicker detection circuit will be described as an example of an embodiment suitable for the present invention.

  FIG. 1 is a block diagram illustrating a configuration example of a fluorescent lamp flicker detection circuit. The fluorescent light flicker detection circuit shown in FIG. 1 receives digitally converted image data output from an XY address type CMOS sensor.

  First, image data is input to the line integration unit 1, the image data is integrated for a predetermined number of pixels (hereinafter referred to as line integration), and integration data (hereinafter referred to as line integration value) is output. The integrated data may be an average value obtained by dividing by a predetermined number of pixels.

  Next, the output of the line integration unit 1 is stored in the previous field integration value storage unit 2. This is because flicker is detected by comparing line integral values between adjacent two fields as will be described later. The reason why line integration is performed is that fluorescent light flicker appears as a change in luminance in the vertical direction, and the flicker component is substantially constant within one line period, so that integration data of the same line is compared between two fields. . Further, in the case of a general moving image format such as NTSC, the time difference between two fields is very small and the subject pattern can be regarded as almost the same. However, when comparing pixel by pixel, a deviation of one pixel becomes a large error. . Therefore, by performing line integration, the influence of the subject shift, particularly the horizontal shift, can be almost ignored. Further, in order to reduce the influence of the deviation in the vertical direction, it is preferable that the line integration is performed not in units of one line but in units of a plurality of lines.

  Subsequently, the flicker detection unit 3 detects flicker from the result of the line integration unit 1 which is the line integration value of the current field and the line integration value of the previous field stored in the previous field integration value storage unit 2.

  The operation of the flicker detection unit 3 will be described in detail. The flicker detection unit 3 divides two inputs. Basically, the current field integral value is divided by the previous field integral value, but the denominator numerator may be reversed. When fluorescent lamp flickers with different patterns are generated in the current field and the previous field, the division results are different in all lines. On the other hand, when the same pattern of fluorescent lamp flicker occurs in the current field and the previous field, the division results are almost the same in all lines. In addition, even when no fluorescent lamp flicker occurs in both fields, the division results are almost the same for all lines. Therefore, if the division result is not constant, the flicker detection is performed. If the division result is constant, the presence / absence of flicker cannot be specified. Therefore, the flicker detection unit 3 outputs flicker detection / non-detection information.

  The shooting environment determination unit 4 determines from the output of the flicker detection unit 3 whether the current shooting environment is under a fluorescent lamp or a non-fluorescent lamp. The flow of this determination in the shooting environment determination unit 4 is shown in FIG. 2 using an example of a moving image format NTSC with a field frequency of 60 Hz.

  First, in the initial electronic shutter speed determination 9, it is determined whether or not the electronic shutter speed is an integral multiple of 1/100 seconds (step 9). In the case of an integral multiple of 1/100 seconds, the electronic shutter speed is changed to a speed other than an integral multiple of 1/100 seconds (step 10). Flicker is detected (step 6). This detection is referred to as primary detection. If flicker is detected as a result of the primary detection, it can be determined that the shooting environment is under a fluorescent lamp with a power frequency of 50 Hz.

  However, if flicker is not detected (not detected in step 6), the shooting environment is either under a non-fluorescent lamp or under a fluorescent lamp with a power frequency of 60 Hz, and the shooting environment cannot be specified. When the electronic shutter is used and the exposure time is an integral multiple of the luminance change period of the fluorescent lamp, flicker does not occur regardless of the field period of the image. Therefore, all the division results in the flicker detection unit 3 in FIG. The lines are almost the same value, and flicker is not detected.

  In step 7, the electronic shutter speed, which is other than an integral multiple of 1/100 second, is changed, and flicker detection is performed again at the changed electronic shutter speed (step 8). This detection is referred to as secondary detection.

  The mechanism of secondary detection will be described with reference to FIG. In FIG. 3, as in FIG. 6, the field period of the image is an integral multiple (1/120 seconds) of the luminance change period of the fluorescent lamp, and the exposure time by the electronic shutter is a non-integer multiple of the luminance change period of the fluorescent lamp. The case is shown. However, the exposure time is divided into two types (1/100 seconds and 1/80 seconds).

  As shown in FIG. 3, according to different exposure times, the phase of the sensor output waveform in the right figure is shifted. Therefore, by changing the exposure time by changing the electronic shutter speed (step 7), if the shooting environment is under a fluorescent lamp, the waveform pattern of the line integral value between the two fields used for the secondary detection is different. Is detected.

  On the other hand, if the shooting environment is under a non-fluorescent lamp, flicker does not occur regardless of the electronic shutter speed. Therefore, the result of division in the flicker detection unit 3 is almost the same for all lines, and flicker is not detected. Therefore, if flicker is detected as a result of the secondary detection 8, it can be determined that the shooting environment is under a fluorescent lamp with a power frequency of 60 Hz, and if it is not detected, the shooting environment is under a non-fluorescent lamp. There are various ways of changing the exposure time.

  As described above, when the output of the flicker detection unit 3 in FIG. 1 indicates flicker detection (in the case of detection in step 6 in FIG. 2), the imaging environment determination unit 4 sets the power frequency to a non-integer multiple of the field frequency of the image. If the output of the flicker detection unit 3 indicates that the flicker is not detected (if not detected in step 6), the shooting environment determination unit 4 determines that the shooting environment has not been determined, and the electronic shutter The speed controller 5 changes the electronic shutter speed (exposure time) of the next field (step 7), and performs the second flicker detection (step 8).

  However, if the exposure time is changed to an electronic shutter speed that is an integral multiple of the luminance change period of the fluorescent lamp, flicker does not occur regardless of the field period of the image. Therefore, the result of division in the flicker detection unit 3 is almost the same for all lines. The flicker is not detected and it is determined that the lamp is under a non-fluorescent lamp regardless of the power supply frequency of the fluorescent lamp. Therefore, when performing the second flicker detection, the exposure time is the luminance change cycle of the fluorescent lamp. The electronic shutter speed is changed to an integral multiple of (step 7).

  At this time, the photographing environment determination unit 4 stores that no flicker was detected in the first flicker detection. If the output of the flicker detection unit 3 indicates flicker detection in the second detection, the imaging environment determination unit 4 determines that the power source frequency is under a fluorescent lamp that is an integral multiple of the field frequency of the image, and flicker non-detection is detected. If it is shown, the shooting environment determination unit 4 determines that the lamp is under a non-fluorescent lamp.

  As described above, according to the present embodiment, it is determined whether the power source frequency is under a fluorescent lamp that is an integer multiple of the field frequency of the image, a fluorescent lamp that is a non-integer multiple of the field frequency of the image, or a non-fluorescent lamp. be able to.

  In the above-described embodiment, the flicker detection unit 3 obtains detection / non-detection by 2-input division. However, it may be obtained by a difference instead of division. In this case, if the electronic shutter speed is different, not only the flicker pattern but also the gain of the entire image increases or decreases in proportion to the speed, so that the exposure time of the input from the line integration unit 1 and the input from the previous field integration value storage unit 2 From the ratio, the flicker detection unit 3 may set the gains of both inputs to 1: 1.

  In the first and second embodiments described above, some or all of them may be configured by software or hardware.

  In the above-described embodiment, the image unit is a field (field cycle 1/60 seconds in NTSC), but the same configuration is also used when the image unit is a frame (frame cycle 1/30 seconds in NTSC). It's okay.

  In the above-described embodiment, NTSC (field cycle 1/60 seconds) is described. However, the same configuration may be used for a moving image format such as a PAL field cycle of 1/50 seconds.

  In addition, various methods such as an interlace method, a progressive method, an analog method, and a digital method can be used.

The structural example of a fluorescent lamp flicker detection circuit is shown. The example of a flow of imaging environment judgment is shown. The phase shift of the luminance change of an image by the difference in electronic shutter speed (exposure time) is shown. An example of a change in luminance of a captured image when the field period is 1/60 seconds and the fluorescent lamp power supply period is 1/50 seconds is shown. An example of a change in luminance of a captured image when the field period is 1/60 seconds and the fluorescent lamp power supply period is 1/60 seconds is shown. An example of a luminance change of a captured image when the field period is 1/60 seconds, the power supply period of the fluorescent lamp is 1/60 seconds, and the exposure time by the electronic shutter is 1/100 seconds is shown.

Explanation of symbols

1 Line integration unit 2 Previous field integration value storage unit 3 Flicker detection unit 4 Imaging environment determination unit 5 Electronic shutter speed control unit

Claims (13)

A method for detecting flicker caused by fluorescent lamps of the first and second luminance periods,
When there is a difference in exposure amount between fields depending on the first exposure period of the image sensor, it is determined that the flicker is caused by a fluorescent lamp having the first luminance cycle,
When there is no difference, change the exposure period of the image sensor,
A flicker detection method for determining flicker caused by a fluorescent lamp having a cycle of the second type of luminance when there is a phase shift in the luminance exposed before and after the change of the exposure period. A method for detecting flicker,
Change the exposure period of the image sensor,
A flicker detection method in which flicker is determined when there is a phase shift in the brightness of the exposure before and after the change of the exposure period. The flicker detection method according to claim 1 or 2,
The image sensor is a CMOS sensor. The flicker detection method according to any one of claims 1 to 3,
The first type of luminance cycle is 1/100 second, and the second type of luminance cycle is 1/120 second. The flicker detection method according to any one of claims 1 to 4,
The duration of the field is 1/60 seconds. The flicker detection method according to any one of claims 1 to 5,
The first exposure period is an exposure period other than an integral multiple or an integral fraction of the first type luminance cycle.   An imaging apparatus for executing the flicker detection method according to claim 1. An integration unit for integrating image data from an XY address type solid-state imaging device;
An integration value storage unit for storing and holding the integration data output by the integration unit for one field period;
A flicker detection unit that determines the presence or absence of flicker from the calculation result of the integration data of the previous field stored and held in the integration value storage unit and the integration data of the current field;
A shooting environment determination unit that determines whether the fluorescent lamp is under the fluorescent lamp and the power frequency of the fluorescent lamp from the flicker detection result output by the flicker detection unit;
An electronic shutter speed control unit for controlling the electronic shutter speed according to the determination result of the imaging environment determination unit;
Fluorescent lamp flicker detection device comprising: The fluorescent lamp flicker detection device according to claim 8,
The flicker detection unit divides the integration data of the previous field by the integration data of the current field. The fluorescent lamp flicker detection device according to claim 8,
The flicker detection unit divides the integration data of the current field by the integration data of the previous field. The fluorescent lamp flicker detection device according to claim 8,
The flicker detection unit corrects the difference between the integration data of the previous field and the integration data of the current field in accordance with the electronic shutter speed to obtain a difference. A fluorescent lamp flicker detection device according to claim 8,
The flicker detection unit determines that flicker is not detected if the calculation result of the integration data of the previous field and the integration data of the current field is substantially constant, and determines flicker detection if the calculation result is not substantially constant. The fluorescent lamp flicker detection device according to claim 8,
The photographing environment determination unit sets a predetermined electronic shutter speed, and if the first flicker detection result is flicker detection, determines that the field frequency and the power supply frequency of the fluorescent lamp are different from each other under a fluorescent lamp. For example, if the second flicker detection result obtained by changing the electronic shutter speed of the next field is flicker detection, it is determined that the field frequency and the power supply frequency of the fluorescent lamp are under the same fluorescent lamp. Judged to be under fluorescent light.

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