JP4591037B2 - Flicker component detection apparatus and flicker component detection method - Google Patents

Description

  The present invention relates to a flicker component detection apparatus and a flicker component detection method suitable for use in detecting the presence or absence of a flicker component of a subject light source at the time of shooting, for example, with a video camera or the like.

  In general, flicker occurs in an image taken by a video camera or the like under an environment illuminated by a lighting device such as a fluorescent lamp depending on the shooting conditions.

  Conventionally, as a method of avoiding the flicker, there is a method of setting the exposure time of the image sensor to an integral multiple of the light source blinking cycle of the subject light source, and as a method of removing the flicker component, a change in the brightness level of the image is detected as an image signal. There is known a method of correcting by changing the amplification factor of the amplifier circuit of the processing unit.

  However, the limitation of the exposure time not only does not give the intended video effect, but also results in a narrow exposure range. In addition, the correction due to the change in the amplification factor of the amplification circuit of the image signal processing unit has the disadvantage that the image quality is lowered, and in addition, it has the effect of making the brightness level constant, so that the change in the brightness of the normal subject is not affected. Have side effects that can result in unnatural images.

  For this reason, it is preferable not to perform the above-described flicker correction processing when the presence or absence of the flicker component of the subject light source is detected and the subject light source does not include the flicker component.

  Conventionally, as a method for detecting the presence or absence of a flicker component of a subject light source, frequency analysis of the brightness level of an image, extraction of a specific frequency using a filter, or comparison of a change amount or a change pattern of a brightness level The method is known.

Also. Conventionally, Patent Document 1 discloses an apparatus that automatically determines the presence / absence or form of an unnecessary brightness change such as flicker in a moving image.
JP 2003-60936 A

  However, the conventional frequency analysis of the brightness level of an image and the detection of the presence or absence of a flicker component of a subject light source that extracts a specific frequency using a filter complicate the circuit configuration and perform digital processing. Even in this case, there is a disadvantage that complicated calculations such as Fourier transform and digital filter are required.

  In addition, the method of comparing change patterns has a disadvantage in that it requires a lot of processing, and the method of detecting the amount of change in brightness level distinguishes between the flicker component of the subject light source and the change in brightness of a normal subject. There was an inconvenience that could not be.

  SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to detect the presence or absence of a flicker component of a subject light source without requiring a complicated configuration and calculation.

The flicker component detection apparatus of the present invention is a flicker component detection apparatus that detects a flicker component of a subject light source from an image signal obtained by using an image sensor, and has a brightness level in the same range for each unit image of the image signal. Brightness detection means for detecting; average value calculating means for calculating an average value level of the brightness levels of a plurality of unit images during a specified period; brightness level of the unit image and the average value level during the specified period A difference calculating means for calculating the difference level between the specified period, a difference adding means for adding the difference levels between the specified periods to obtain an absolute value level, and a difference for integrating the absolute value levels of the difference levels between the specified periods. has an absolute value integrating means, and the flicker component contained in the object light source, the absolute value level of substantially becomes zero output by multiplying the difference integrating means to specify circumference period When the absolute value level of the difference level integrated and output by the difference absolute value integration means during the specified period is a constant amount, the absolute value level output by the difference integration means during the specified period is approximately When the absolute value level of the difference level output by the difference absolute value integrating means becomes a constant amount during a specified period, the presence of a flicker component of the subject light source is detected.

The flicker component detection method of the present invention is a flicker component detection method in which a flicker component of a subject light source is detected from an image signal obtained using an image sensor, and the same range for each unit image of a plurality of unit images during a specified period. The average value level of the brightness level is calculated and the difference level between the average level and the brightness level of the unit image during the specified period is calculated, and the difference level is integrated by adding up the difference level between the specified periods. The absolute value level is obtained and the absolute value level of the difference level during the specified period is integrated to obtain the absolute difference value integration level. The subject light source is obtained using the difference integration absolute value level and the difference absolute value integration level. of a flicker component detection method for detecting the presence or absence of a flicker component, the flicker component contained in the object light source, the absolute value les difference sum between the specified period Is a flicker component whose difference absolute value integration level during a specified period is a constant amount, the difference integration absolute value level is approximately zero during the specified period, and the difference absolute value integration level during the specified period. Is detected as having a flicker when it is detected that a predetermined amount is detected .

  According to the present invention, the average value level of the brightness levels of the plurality of unit images during the specified period is calculated, and the difference level between the average level and the brightness level of the unit images during the specified period is calculated. The difference level between the specified periods is integrated to obtain the difference integrated absolute value level, and the difference level absolute value level between the specified periods is integrated to obtain the difference absolute value integrated level. The difference absolute value integration level is used to detect the presence or absence of the flicker component of the subject light source, and the presence or absence of the flicker component of the subject light source can be detected without requiring a complicated configuration or calculation.

  Hereinafter, an example of the best mode for carrying out the flicker component detection apparatus and the flicker component detection method of the present invention will be described with reference to the drawings.

  First, an example of a video camera to which the flicker component detection apparatus and the flicker component detection method according to this example are applied will be described with reference to FIG. In FIG. 3, reference numeral 1 denotes an image sensor composed of a solid-state image sensor or the like that images the subject 6.

  An image signal obtained by using the image pickup device 1 is supplied to the image signal processing unit 3 through the sampling hold circuit and the analog-digital conversion circuit 2. The image signal processing unit 3 includes an amplification circuit 3a that amplifies the image signal, a brightness level detection unit 3b that detects the brightness level of the image signal, and the like.

  In FIG. 3, reference numeral 4 denotes an exposure time control unit that controls the exposure time of the image sensor 1. The sampling hold circuit and analog-digital conversion circuit 2, the image signal processing unit 3, and the exposure time control unit 4 are controlled in the same manner as in the prior art by a central control unit 5 comprising a microcomputer.

  The central controller 5 according to this example is configured to perform the flicker correction process only when the subject light source 7 of the subject 6 has a flicker component.

  In this example, the central controller 5 detects the presence or absence of the flicker component of the subject light source 7 as shown in the functional block diagram of FIG. 1 and the flowchart of FIG.

  The flicker component detection apparatus and the flicker component detection method according to this example will be described with reference to FIGS. 1, 2, 4 and 5. The video camera according to this example is an NTSC system in which the frequency of the vertical synchronization signal is 60 Hz. Further, the image unit according to this example is one field.

  The subject light source 7 is a fluorescent lamp having a power supply AC frequency of 50 Hz. In this case, since the flicker frequency is 100 Hz, the flicker frequency is 20 Hz. In this example, the specified period T0 is set to 3 fields (4/60 seconds) in accordance with the flicker frequency 20 Hz.

  In this example, the brightness level of the image signal obtained using the image sensor 1 is detected by the brightness level detection unit 3b as a unit image (one field). Assume that the brightness level of each field at this time is as shown in FIG. 4A.

  In this example, first, as shown in the flowchart of FIG. 2, the average value level S of the brightness levels of the three unit images F1, F2, and F3 is obtained in the plurality of examples of the designated period T0 (step S1).

  Next, a difference level between the brightness level of the unit images F1, F2 and F3 in the specified period T0 and the average value level S obtained in step S1 is calculated (step S2). In this case, the difference levels of the unit images F1, F2, and F3 are, for example, α, β, and γ as shown in FIG. 4B.

  Next, the absolute value level | α + β + γ | of the difference level integration during the specified period T0 is calculated (step S3) and the absolute value integration level (| α | + | β |) of the difference level during the specified period T0 is calculated. + | Γ |) is calculated (step S4).

Next, the index C is calculated from the difference integrated absolute value level | α + β + γ | and the difference absolute value integrated level (| α | + | β | + | γ |).
C = (| α | + | β | + | γ |) ÷ | α + β + γ |
The presence or absence of a flicker component is detected from this index C (step S5). An example of a functional block diagram for executing the flowchart of FIG. 2 is shown in FIG. Referring to FIG. 1, in FIG. 1, reference numeral 10 denotes an input terminal to which a brightness level signal as shown in FIG. 4A of the unit images F1, F2, and F3 is supplied, and is obtained at the brightness level input terminal 10. The brightness level signal is supplied to the adder circuit 11a and the delay circuit 11b of one unit image (one field) constituting the average value calculation circuit 11 for obtaining the average value level of T0 for the specified period, and the one unit image of the delay circuit 11b The delayed output signal is supplied to the adder circuit 11a and supplied to the adder circuit 11a via the delay circuit 11c between one unit images (between one field).

  In this case, on the output side of the adder circuit 11a, for example, a brightness level obtained by adding the brightness levels of the three unit images F1, F2, and F3 is obtained. The output signal of the adder circuit 11a is 1/3. Is supplied to the dividing circuit 11d, and the average value level S of the designated period T0 is obtained on the output side of the dividing circuit 11d.

  The output signal of the division circuit 11d, that is, the average value level S obtained on the output side of the average value circuit 11 is supplied to the subtraction circuit 12 for obtaining the difference level, and the brightness as shown in FIG. A level signal is supplied to the subtraction circuit 12.

  In this case, signals of difference levels α, β, and γ are obtained on the output side of the subtracting circuit 12 as shown in FIG. The difference level α, β, γ signals obtained on the output side of the subtracting circuit 12 are added to the adding circuit 13a constituting the difference integrating circuit 13 for obtaining the difference integrated absolute value level and the delay circuit 13b between the unit images (between one field). To the absolute value circuit 14a constituting the absolute difference integration circuit 14 for obtaining the absolute difference value integration level.

  In the difference integrating circuit 13, an output signal delayed by one unit image (between one field) of the one unit image delay circuit 13b is supplied to the adder circuit 13a and is added through the one unit image delay circuit 13c. 13a.

  In this case, a difference integration level (α + β + γ) obtained by integrating the difference levels of the designated period T0 is obtained on the output side of the addition circuit 13a. The difference integration level (α + β + γ) obtained on the output side of the addition circuit 13a is supplied to the absolute value circuit 13d, and the difference integration absolute value is output to the output side of the absolute value circuit 13d, that is, the output side of the difference integration circuit 13. The level | α + β + γ | is obtained.

  Further, in the difference absolute value integration circuit 14, the output signal of the absolute value circuit 14a is supplied to the addition circuit 14b and to the delay circuit 14c between one unit images (between one field), and the output signal of this delay circuit 14c is added. This is supplied to the circuit 14b and supplied to the adding circuit 14b via the delay circuit 14d between the unit images.

  In this case, on the output side of the addition circuit 14b, that is, on the output side of the difference absolute value integration circuit 14, the difference absolute value integration level (| α | + | β | + | γ |) is obtained.

In this example, the difference integrated absolute value level | α + β + γ | and the difference absolute value integrated level (| α | + | β | + | γ |) of the circuit difference integrating circuit 13 are supplied to the dividing circuit 15, Index C as shown in
C = (| α | + | β | + | γ |) ÷ | α + β + γ |
This index C is obtained at the index output terminal 16.

  Here, when the brightness changes periodically like flicker, this difference integrated absolute value level | α + β + γ | becomes substantially zero, and this difference absolute value integrated level (| α | + | β | + | γ |) Will have a certain amount.

  The brightness levels of the fields F1, F2, and F3 when a flicker component is not included, such as a light source such as sunlight or an incandescent lamp, are constant as shown in FIG. 5A, and the difference level from the average value level is as shown in FIG. 5B. It becomes almost zero.

  FIG. 5B shows a level change corresponding to a side effect component when the image signal processing unit 3 performs the flicker correction process.

  If the brightness of the subject does not change, the difference integrated absolute value levels | α + β + and γ | and the difference absolute value integrated level (| α | + | β | + | γ |) are both substantially zero. When the brightness changes, the difference integrated absolute value level | α + β + γ | and the difference absolute value integrated level (| α | + | β | + | γ |) both have a constant amount.

  Therefore, by monitoring the difference integrated absolute value level | α + β + γ | and the difference absolute value integrated level (| α | + | β | + | γ |), it is possible to determine the presence or absence of the flicker component of the subject light source 7. .

  An index C for determining the presence or absence of a flicker component can be created by taking a ratio of the difference accumulated absolute value level | α + β + γ | and the difference absolute value accumulated level (| α | + | β | + | γ |). The presence or absence of a flicker component can be determined by comparing C with an appropriate threshold value.

  In this example, when the subject light source 7 includes a flicker component, the difference integrated absolute value level | α + β + γ | is substantially zero, and the difference absolute value integrated level (| α | + | β | + | γ |) is approximately zero. Since the amount is constant, the index C has a large value.

  When the flicker component is not included, the difference integrated absolute value level | α + β + γ | and the difference absolute value integrated level (| α | + | β | + | γ |) are both substantially zero. This index C can be made substantially zero by applying a restriction so that the value level | α + β + γ | does not become zero.

  When the brightness of the subject 6 changes, the difference integrated absolute value level | α + β + γ | and the difference absolute value integrated level (| α | + | β | + | γ |) show substantially the same amount. The index C indicates a value close to “1”. Therefore, if an appropriate value larger than the threshold “1” is set, it can be determined that the flicker component is included when the index C is larger than the threshold.

  Usually, there is a rare case where the index C exceeds the threshold value due to a change in the brightness of the subject 6, but since it does not continue, it does not affect the suppression of side effects by the correcting means. Further, if necessary, if it is determined that the flicker component is present only when the index C exceeds the threshold value a plurality of times in succession, the flicker component is not erroneously detected even in a short time.

  According to this example, the average value level of the brightness levels of a plurality of, for example, three unit images in the specified period T0 is calculated, and the brightness levels of the unit images F1, F2, and F3 in the specified period T0 and the average value level are calculated. The difference levels α, β, γ with respect to S are calculated, and the difference levels α, β, γ of the specified period T0 are integrated to obtain a difference integrated absolute value level | α + β + γ | and the difference level between the specified periods The absolute value level of the difference is integrated to obtain the difference absolute value integration level (| α | + | β | + | γ |). This difference integration absolute value level | α + β + γ | and this difference absolute value integration level (| α | + | Β | + | γ |) is used to detect the presence or absence of the flicker component of the subject light source 7, and the presence or absence of the flicker component of the subject light source 7 is detected without requiring a complicated configuration or calculation. be able to.

  In the above example, the unit image has one field, but this unit image may be anything as long as it has a time difference in exposure and there is a means for detecting the brightness level of the image signal. The means for detecting the brightness level of the image signal may also be used as the brightness level detection means for the image signal of an automatic exposure control device mounted on an imaging device such as a video camera.

  Further, the present invention is not limited to the above-described example, and various other configurations can be adopted without departing from the gist of the present invention.

It is a block diagram which shows the example of the best form for implementing this invention flicker component detection apparatus. It is a flowchart which shows the example of the best form for implementing the flicker component detection method of this invention. It is a block diagram which shows the example of a video camera. It is a diagram with which it uses for description of this invention. It is a diagram with which it uses for description of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image pick-up element, 3 ... Image signal processing part, 3b ... Brightness level detection part, 5 ... Central controller, 6 ... Subject, 7 ... Subject light source, 10 ... Brightness level input terminal, 11 ... Average value circuit, 12 ... Subtraction circuit, 13... Difference integration circuit, 14... Absolute difference integration circuit, 15.

Claims (6)

In a flicker component detection apparatus that detects a flicker component of a subject light source from an image signal obtained using an image sensor,
Brightness detection means for detecting a brightness level in the same range for each unit image of the image signal;
An average value calculating means for calculating an average value level of the brightness levels of a plurality of unit images during a specified period;
A difference calculating means for calculating a difference level between the brightness level of the unit image during the specified period and the average value level;
Difference accumulation means for accumulating the difference levels between the specified periods to obtain an absolute value level;
Difference absolute value integration means for integrating the absolute value level of the difference level between the specified periods;
Have
As the flicker component contained in the subject light source, the absolute value level integrated and output by the difference integration means during the specified period becomes substantially zero, and is output by integration by the difference absolute value integration means during the specified period. When the flicker component is such that the absolute value level of the difference level is a certain amount,
The absolute value level output by the difference integration means during the specified period becomes substantially zero, and the absolute value level of the difference level output by the difference absolute value integration means during the specified period becomes the constant amount. flicker component detection apparatus adapted to detect the presence of flicker component of the object light source. The flicker component detection apparatus according to claim 1,
A flicker component detection device equal to an integral multiple of a flicker period during the specified period. The flicker component detection apparatus according to claim 1,
A flicker component detection apparatus that creates an index indicating the presence or absence of a flicker component from a ratio between an output level of the difference accumulation means and an output level of the difference absolute value accumulation means. In a flicker component detection method in which a flicker component of a subject light source is detected from an image signal obtained using an image sensor,
Detecting a brightness level in the same range for each unit image of the image signal;
Calculating an average value level of the brightness levels of a plurality of unit images during a specified cycle and calculating a difference level between the brightness level of the unit images during the specified cycle and the average value level; The difference level is integrated to obtain a difference integrated absolute value level, and the absolute value level of the difference level during the specified period is integrated to obtain a difference absolute value integrated level,
A flicker component detection method for detecting the presence or absence of a flicker component of the subject light source using the difference integrated absolute value level and the difference absolute value integrated level ,
When the flicker component included in the subject light source is a flicker component in which the difference integrated absolute value level between the specified cycles is substantially zero and the difference absolute value integrated level between the specified cycles is a constant amount,
A flicker component detection method for detecting presence of flicker when it is detected that the difference integrated absolute value level becomes substantially zero during the specified period and the difference absolute value integrated level during the specified period becomes a constant amount . In the flicker component detection method according to claim 4,
The flicker component detection method equal to an integral multiple of the flicker period during the specified period. In the flicker component detection method according to claim 4,
A flicker component detection method in which an index indicating the presence or absence of a flicker component is created from a ratio between the difference integrated absolute value level and the difference absolute value integrated level.

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