JP2002152604A - Device for eliminating flicker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a flicker due to fluorescent light in a digital camera using a solid-state imaging units in which the total quantity of light emitted within the exposure time of each pixel are different for each line even in the same frame or field. SOLUTION: The occurrence itself of the flicker is eliminated by making the exposure time of the solid-state imaging unit 12 to be an integer-multiple of 1/100 or 1/120 seconds, and a flicker correction gain is calculated for each area where flicker components are considered almost the same in one frame to perform flicker correction. Thus, a stable and excellent image without S/N dispersion within one frame and with no effect of the flicker on a moving object can be obtained without making a circuit large in scale.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flicker removing apparatus for preventing fluorescent lamp flicker in a digital camera using an image pickup device affected by fluorescent lamp flicker.

[0002]

2. Description of the Related Art A general fluorescent lamp flickering with a commercial AC power supply has a frequency of 1/100 sec.
In the case of Hz, blinking is repeated at a period of 1/120 seconds. When such an incident light is converted into an electric signal by an image sensor and read out, when an image pickup tube or a MOS solid-state image sensor is used, the exposure start time differs depending on the position of the pixel to be read out. (In this description, these are collectively referred to as a frame.) Also, the sum of the amounts of light incident within the exposure time of each pixel will be different. Therefore, even in the same frame, 1 /
A bright portion and a dark portion occur at a period of 100 seconds or 1/120 seconds. Such a phenomenon is flicker.

Conventionally, in order to obtain a good image which is not affected by flicker occurring in the same frame as described above, one frame is divided into regions in which flicker components can be regarded as substantially the same, for example, one line at a time. A flicker correction device for obtaining a flicker correction gain for each area has been proposed.

In this case, regardless of the presence or absence of flicker,
Since the correction is always performed by obtaining the flicker correction gain, a flicker removing device is not particularly required. However, the area where the flicker component can be regarded as substantially the same is small, and the number of areas is large. Therefore, providing a circuit for obtaining the flicker correction gain for each area increases the circuit scale. Further, since gains are different at various points in one frame, variations in S / N occur in one frame, which degrades image quality. Further, since a moving subject is unstable, a circuit for stabilization is required.

As another proposal which does not have the above-mentioned problem, an exposure time of an image sensor is set to an integral multiple of 1/100 second or 1/1.
In some cases, even if the exposure start time is changed to an integral multiple of 20 seconds, the sum of the amounts of light incident within the exposure time of each pixel is the same, thereby preventing the occurrence of flicker itself. In this case, 1/100
The photographer decides whether to make an integral multiple of seconds or an integral multiple of 1/120 seconds, or a flicker consisting of a photometric element provided separately from the image sensor and a blinking period of the light source. It was judged by the removal device.

FIG. 5 shows a conventional example in which the photometric element is provided. The solid-state imaging device 51 includes a driving circuit 52
And converts the optical image of the subject into an electrical signal and outputs the electrical signal. The signal processing circuit 53 generates and outputs a luminance signal Y from the signal output from the solid-state imaging device 51.

On the other hand, the photometric element 54 detects the illuminance of the light source and sends it to the blinking cycle detecting circuit 55,
Detects whether the flicker cycle of the light source is 1/100 second or 1/120 second from the change in illuminance. The exposure time determination circuit 56 calculates the exposure time from the output of the blink cycle detection circuit 55 by 1 /.
It decides whether to be an integral multiple of 100 seconds or an integral multiple of 1/120 seconds, calculates a suitable multiple from the luminance signal Y, determines an exposure time, and instructs the drive circuit 52. Drive circuit 52
Drives the solid-state imaging device 51 in accordance with this.

As described above, if the exposure time of the solid-state imaging device is automatically set to an exposure time at which flicker does not occur, a good image free from the influence of flicker occurring within the same frame can be obtained.

[0009]

However, when such a conventional flicker removing device is used, it is necessary to provide a photometric element in addition to the solid-state image pickup device, which increases the number of components and increases the number of components on the surface of the camera housing. The need to provide a light-receiving unit for use has also caused restrictions on design.

Therefore, the present invention provides a favorable circuit which does not increase the circuit scale, does not vary the S / N within one frame, does not become unstable with respect to a moving subject, and has no influence of flicker. An object of the present invention is to provide a flicker removing device capable of obtaining an image.

[0011]

In order to solve the above-mentioned problems, in the flicker elimination apparatus of the present invention, the total amount of light incident within the exposure time of each pixel for each line even in the same frame or field. Are different from each other, extraction means for extracting a luminance signal component from a video signal output from the solid-state imaging element, and a luminance component for each line obtained by the extraction means are integrated, and an average value for each line is obtained. And comparing the average value with the same line in a plurality of frames or fields, and detecting the flicker based on the comparison result, and controlling the exposure time of the solid-state imaging device based on the detection result of the detection unit. And control means for performing the control.

According to this means, the occurrence of flicker is prevented by setting the exposure time of the solid-state imaging device to an integral multiple of 1/100 second or an integral multiple of 1/120 second. As a result, it is possible to obtain a stable and favorable image free from the influence of flicker on a moving subject without increasing the circuit scale, without variation in S / N within one frame.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a system diagram for explaining a first embodiment of the present invention. In FIG. 1, a solid-state imaging device 12 driven by a drive circuit 11 converts an optical image of a subject into an electric signal and outputs the electric signal. The signal processing circuit 13 to which the output is supplied generates a luminance signal Y from the output signal obtained from the solid-state imaging device 12 and supplies the luminance signal Y to the luminance average calculation unit 141 of the flicker detection circuit 14. Brightness average calculator 141
Then, the average value of the luminance signals in one line is calculated by integrating the luminance signals of one line.

A luminance average calculation line selection signal generator 142
The vertical synchronizing signal a, the horizontal synchronizing signal b, a 1/200 second setting signal c indicating how many 1/200 seconds correspond to a period, and 1/240 seconds correspond to a number of lines. A 1/240 second setting signal d and a light source frequency setting signal e are supplied, respectively.

Here, when the light source frequency setting signal e instructs to detect flicker of a 50 Hz fluorescent lamp, 1 /
A luminance average calculation line selection signal f is output so as to select a line for calculating a luminance average at intervals of 200 seconds, and when the light source frequency setting signal e instructs to detect flicker of a 60 Hz fluorescent lamp, the interval is 1/240 seconds. The luminance average calculation line selection signal f is selected so that
Is output.

In this example, five horizontal lines are selected. However, the number of horizontal lines is not limited to five. The luminance average for each of the five lines whose exposure start times are different from each other by の of the blinking cycle of the light source is determined by the luminance average calculation line selection signal f, the output of the luminance average calculation unit 141, and the selection unit 143 and the luminance average storage units 1441 to 1445. Get the value. It is assumed that the exposure start time is the earliest in the luminance average storage section 1441, and thereafter, in the order of the luminance average storage sections 1442, 1443, 1444, and 1445. In this example, five lines share the luminance average calculation unit 141, but the luminance average calculation unit 141 may be provided for each line.

Next, the average luminance value of each line is input to each of the change detection units 1451 to 1455 from the previous frame, where the average luminance value of the current frame and the average luminance value of the previous frame are compared to determine whether the increase / decrease / no change has occurred. judge. At this time, a circuit that does not increase / decrease unless there is a change above a certain level may be provided to stabilize the detection result.

Change detection unit 1451-1 from previous frame
The output of 455 is input to the comparison / determination unit 146, which detects the flicker, and outputs a flicker detection signal g therefrom.

In the comparison / determination unit 146, a change detection unit 145 from a previous frame extends over an arbitrary plural frames.
1, 1453, 1455, and the outputs of the change detection units 1452, 1454 from the previous frame are the same, and the change detection units 1451, 1453,
Output of 1455 and change detection unit 145 from previous frame
When the output of 2,145 indicates an opposite change, it is determined that flicker exists.

The flicker detection signal g is supplied to an exposure time determination circuit 15, and when a signal indicating the presence of a 50 Hz fluorescent lamp flicker is sent, the exposure time is set to an integral multiple of 1/100 second, and the 60 Hz flicker is detected. When a signal indicating presence is sent, the value is set to an integral multiple of 1/120 seconds. And
In each case, a suitable multiple is calculated from the luminance signal Y, the exposure time is determined, and the driving circuit 11 is instructed. In accordance with this instruction, the drive circuit 11 drives the solid-state imaging device 12.

In this manner, flicker can be detected without providing a photometric element separately from the solid-state imaging device 12, and the occurrence of flicker can be prevented based on the detection result.

FIG. 2 shows an example of selecting a luminance average calculation line in this embodiment. This is a frame rate of 3
This is a case where a flicker caused by a 50 Hz fluorescent lamp is detected at 0 frames / sec.

In this example, the luminance signal obtained by the signal processing is integrated. However, for example, the output of the solid-state imaging device 12 in which the color filter array is a primary color Bayer array is integrated as it is to calculate an average luminance value. It is also possible. in this case,
The output of the solid-state imaging device 12 is integrated by two integrators, that is, a line with RGRG... And an adjacent line with GBGB.
Let the average value of the signal be the average luminance value. Lines 1, 2, 3, 4, and 5 shown in FIG. 2 are also lines 1, 2, 3, 4, and 5 in pairs of two lines.

FIG. 3 is a system diagram for explaining a second embodiment of the present invention. The same components as those in the embodiment of FIG. 1 are denoted by the same reference numerals and described.

That is, driven by the drive circuit 11, the solid-state image pickup device 12 converts an optical image of a subject into an electric signal and outputs the electric signal. From the output, the signal processing circuit 13 generates and outputs a luminance signal Y.

50 Hz fluorescent lamp flicker detection circuit 14a
Detects flicker caused by a 50 Hz fluorescent lamp from a change in the average luminance value of a plurality of lines whose exposure start time differs by 1/200 second. The 60 Hz fluorescent lamp flicker detection circuit 14b detects a plurality of lines whose exposure start time differs by 1/240 second. The flicker caused by the 60 Hz fluorescent lamp is detected from the change of the average luminance value of the line.

The exposure time determination circuit 15 reduces the exposure time by 1/50 when the 50 Hz fluorescent lamp flicker detection circuit 14a sends the flicker detection signal g1 indicating the presence of flicker.
The flicker detection signal g2 indicating the presence of flicker is obtained by setting the 60 Hz fluorescent lamp flicker detection circuit 14b to an integral multiple of 100 seconds.
Is sent, it is set to an integral multiple of 1/120 seconds.
Then, in each case, a suitable multiple is calculated from the luminance signal Y, the exposure time is determined, and the driving circuit 11 is instructed. The drive circuit 11 drives the solid-state image pickup device 12 according to this.

In this embodiment, when the fluorescent lamp flicker does not exist, the exposure time of the solid-state imaging device 12 can be freely set as usual, and the exposure of the solid-state imaging device 12 can be set only when the fluorescent lamp flicker exists. By setting the time automatically to an exposure time at which flicker does not occur, it is possible to obtain a good image free from the influence of flicker occurring within the same frame.

FIG. 4 is a system diagram for explaining a third embodiment of the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals.

The solid-state image pickup device 12 driven by the drive circuit 11 converts an optical image of a subject into an electric signal and outputs it, and supplies the output to a signal processing circuit 13. The signal processing circuit 13 generates and outputs a luminance signal Y from the supplied signals. The exposure time determination circuit 15 sets the exposure time of the solid-state imaging device 12 to an integral multiple of 1/100 seconds or an integral multiple of 1/120 seconds, and calculates a suitable multiple from the luminance signal Y.
Determine the exposure time. Further, the flicker cycle h of the light source indicating whether the current time is an integral multiple of 1/100 second or 1/120 second is sent to the 50 Hz / 60 Hz fluorescent lamp flicker detection circuit 14c.

The 50 Hz / 60 Hz fluorescent lamp flicker detection circuit 14 c uses the exposure time determination circuit 15 to set the exposure time to 1/1.
When the time is an integral multiple of 00 seconds, flicker does not occur under a 50 Hz fluorescent lamp, so that only the flicker by the 60 Hz fluorescent lamp needs to be detected. Conversely, when the exposure time determination circuit 15 sets the exposure time to an integral multiple of 1/120 second, flicker does not occur under a 60 Hz fluorescent lamp, so that only flicker by a 50 Hz fluorescent lamp need be detected. Therefore, when the exposure time determination circuit 15 sets the exposure time to an integral multiple of 1/100 second, the 50 Hz / 60 Hz fluorescent lamp flicker detection circuit 14c calculates the average luminance value of a plurality of lines whose exposure start times differ by 1/240 second. Is detected from the change of the flicker, the flicker caused by the 60 Hz fluorescent lamp is detected.
Instructs to be an integral multiple of 0 seconds. Also, if the exposure time is 1
When the exposure start time is an integral multiple of / 120 seconds, flicker caused by a 50 Hz fluorescent lamp is detected from a change in the average luminance value of a plurality of lines whose exposure start time is different by 1/200 second. The signal g instructs the exposure time determination circuit 15 to set the exposure time to an integral multiple of 1/100 second.

With this arrangement, even when the fluorescent lamp flicker does not exist, the exposure time of the solid-state imaging device 12 is reduced to 1/10.
Although it becomes an integral multiple of 0 seconds or an integral multiple of 1/120 seconds, the flicker detection circuit is one in comparison with the second embodiment.
Can be reduced to one.

[0033]

As described above, according to the flicker removing apparatus of the present invention, it is not only necessary to provide a photometric element, but also to remove flicker generated by a specific solid-state image pickup device without increasing the number of components. be able to.

[Brief description of the drawings]

FIG. 1 is a system diagram for explaining a first embodiment of the present invention.

FIG. 2 is an explanatory diagram for explaining the operation of FIG. 1;

FIG. 3 is a system diagram for explaining a second embodiment of the present invention.

FIG. 4 is a system diagram for explaining a third embodiment of the present invention.

FIG. 5 is a system diagram for explaining a conventional flicker removing device.

[Explanation of symbols]

11: drive circuit, 12: solid-state imaging device, 13: signal processing circuit, 14, 14a to 14c: flicker detection circuit, 14
1: luminance average calculation unit; 142: line selection signal generation unit;
143 selection unit, 1441-1445 luminance average storage unit, 1451-1455 change detection unit, 146 comparison determination unit, 15 exposure time determination circuit.

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Claims (5)

[Claims] 1. A solid-state imaging device in which the sum of the amounts of light incident within the exposure time of each pixel is different for each line even in the same frame or field, and a luminance is selected from video signals output from the solid-state imaging device. Extracting means for extracting a signal component; integrating a luminance component for each line obtained by the extracting means; obtaining an average value for each line; comparing average values of the same line in a plurality of frames or fields; A flicker removing apparatus comprising: a detecting unit that detects flicker based on a result; and a control unit that controls an exposure time of the solid-state imaging device based on a detection result of the detecting unit. 2. The luminance average calculating means for integrating the luminance for each of a plurality of lines whose exposure start time is different from each other by の of the blinking period of the light source, and calculating an average luminance value in each line, Change detecting means for detecting a change in the output of the luminance average calculating means from a previous frame; comparing means for comparing outputs of the change detecting means for each of the plurality of lines; and starting exposure over a plurality of frames by the comparing means. And signal generating means for generating a signal indicating the presence of flicker when it is detected that lines which differ in time by half of the blinking period of the light source change in the opposite direction. The flicker removing device according to claim 1, wherein: 3. The flicker removing apparatus according to claim 1, wherein said detecting means outputs a flicker detection signal when the comparison result is equal to or higher than a predetermined level. 4. The flicker removing apparatus according to claim 1, wherein said detecting means detects a fluorescent lamp flicker of 50 Hz and a fluorescent lamp flicker of 60 Hz. 5. The exposure time of said solid-state image sensor is reduced to 1/10.
When it is an integral multiple of 0 seconds, the blink cycle of the light source is 1/1.
20 seconds, and the exposure time of the solid-state imaging device was 1/120.
When it is an integral multiple of seconds, the blinking cycle of the light source is 1/10
2. A flicker removing device according to claim 1, further comprising means for setting the time to 0 seconds, wherein both flicker caused by the light source when the commercial power frequency is 50 Hz and flicker caused by the light source when the commercial power frequency is 60 Hz can be detected. .