KR20090074446A - Method for decreasing flicker - Google Patents

Abstract

A method for reducing a flicker is provided to adjust a pixel clock signal when shutter speed is faster than a preset threshold value, thereby synchronizing the adjusted pixel clock signal with a horizontal synchronization signal. An image signal processor detects illuminance of image light which is incident through an image sensor(S31). When illuminance is high, the image signal processor receives a smaller amount of light by quickly adjusting shutter speed(S32). The image signal processor determines whether the adjusted shutter speed is faster than a preset shutter speed threshold value(S33). When the shutter speed is faster than the preset shutter speed threshold value, the image signal processor adjusts a blank interval of the pixel clock signal until a pixel clock signal is matched with the horizontal synchronization signal(S34,S35).

Description

How to reduce flicker {Method for decreasing flicker}

The present invention relates to a method for reducing the flicker phenomenon in imaging.

In general, in the case of a camera with automatic shutter speed adjustment, as the illumination level increases, the camera's shutter speed becomes faster and operates up to 30 fps (frame per sec).

For example, a 1,500 Lux fluorescent light that is directly lit by a commercial AC power source at 50 Hz produces a change in illuminance at 1/100 second intervals. Under these circumstances, the camera's shutter speed is up to 30 fps, i.e., 1/120 sec. It is operated until.

By the way, when photographing a subject with a camera under the illumination of a fluorescent lamp which is turned on by a commercial AC power supply directly, the difference of the frequency (two times the commercial AC power supply frequency) of the illumination intensity change (light quantity change) of a fluorescent lamp and the shutter speed of a camera As a result, there is a problem that a change in temporal contrast, that is, flicker occurs in the video signal of the imaging output.

For example, when photographing a subject by a camera under a fluorescent lamp having a commercial AC power frequency of 50 Hz, as the illuminance level of the fluorescent lamp is increased as shown in FIG. It operates up to 30fps.

Therefore, since the shutter speed of the camera has a maximum of 1/120 second while the period of illumination intensity change of the fluorescent lamp is at a maximum of 1/120 seconds, the exposure timing of each field is shifted with respect to the illumination intensity change of the fluorescent lamp, and the exposure amount of each pixel It is changed for each field.

As a result, since the exposure timing of the shutter speed according to the illuminance change period, such as a fluorescent lamp, does not coincide, there is a problem that the flicker section 11 is repeatedly generated at a predetermined period.

The present invention improves the flicker phenomenon when the illuminance change period and the shutter speed exposure timing do not coincide.

According to an embodiment of the present invention, a shutter speed is set to a high speed when light having an illuminance higher than an illuminance threshold is input, and a pixel clock signal that is an image frame output clock is adjusted when the shutter speed is faster than a preset shutter speed threshold. Synchronizing with the horizontal synchronization signal.

The illuminance threshold is 1,500 Lux, and the shutter speed threshold is 1/100 seconds.

Adjusting the pixel clock signal increases the blank period of the pixel clock signal to synchronize the horizontal clock signal.

According to the present invention, when the shutter speed exceeds a preset threshold, the pixel clock signal is adjusted to synchronize with the horizontal synchronization signal, thereby improving flicker.

Hereinafter, the detailed description of the preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the following description of the reference numerals to the components of the drawings it should be noted that the same reference numerals as possible even if displayed on different drawings.

2 is a block diagram of an image photographing apparatus for reducing flicker according to an exemplary embodiment of the present invention.

The granular part 30 includes a photographing sensor such as a CMOS and a lens assembly to obtain an analog image signal from light incident from a subject according to depth and shutter speed adjustment. The analog signal from the winning part 30 passes through the A / D converter 40 and the illuminance of the corresponding video signal is detected by the image signal processing unit 20.

The shutter control module 22 in the image signal processing unit 20 controls the lens driving driver 50 to adjust the shutter speed according to the magnitude of illuminance of the detected image signal so that the photographing is performed. When the intensity of the incident image image is low, the shutter speed is opened for a relatively long time by lowering the shutter speed to receive a lot of incident light. When the intensity of illumination is high, the shutter speed is increased by the shutter speed so that a small amount of incident light is received.

As shown in FIG. 1, in the case of a fluorescent image having an illumination change cycle of 1/100 second, as the illumination level is high, the shutter speed of the camera is increased to operate up to 30 fps, that is, the cycle of the illumination change of the fluorescent image is 1 At / 100 sec, the camera shutter speed will have a maximum of 1/120 sec. However, when the illumination intensity change period of the fluorescent lamp is 1/100 second and the shutter speed is 1/120 second as described above, the exposure timing of each field is shifted with respect to the illumination intensity change of the fluorescent lamp, so that flicker occurs and black streaks appear on the screen. It becomes recognized as a shape, and causes image quality deterioration.

That is, when the light is taken under a light source environment such as a fluorescent lamp having a high illuminance of 1,500 Lux or more and a change in illuminance (1/100 second cycle), the shutter speed also becomes faster. Faster than the speed threshold) may cause flicker, such as black stripes.

In order to improve flicker when the shutter speed becomes faster than the shutter speed threshold as described above, the PCLK control module 21 in the image signal processing unit 20 varies the pixel clock signal PCLK and the PCLK and the horizontal synchronization signal H_Sync. Match the motive with

The pixel clock signal PCLK is a clock signal used to output an image, and the image signal processor outputs an image data frame in accordance with the pixel clock signal. Therefore, when the pixel clock signal is fast, more image data frames are output. On the other hand, when the pixel clock signal is late, the image data frames are output less.

The present invention improves the flicker phenomenon by slowing down the pixel clock signal and synchronizing with the horizontal synchronization signal when the shutter speed becomes faster than the preset shutter speed threshold.

3 is a flowchart illustrating a process of reducing flicker according to an exemplary embodiment of the present invention.

The illuminance of the image light source, which is imaged through an image sensor such as a CMOS, is detected (S31), and when the illuminance is high, the image signal processor of the image capturing apparatus adjusts the shutter speed quickly (S32) to receive less incident light. For example, when the incident light source is a fluorescent lamp having an illuminance of 1,500 Lux or more, the imaging apparatus speeds up the shutter speed up to 1/120 second.

It is determined whether the adjusted shutter speed is faster than the preset shutter speed threshold (S33), and when the pixel clock signal PCLK is synchronized with the horizontal synchronization signal H_Sync when it is faster than the shutter speed threshold (S35). The blank period of the pixel clock signal is adjusted until S34.

For example, when an incident light source has a 1/100 second illuminance level change due to a 50 Hz frequency power supply, when the shutter speed is set to 1/120 second faster than the 1/100 second, the set shutter speed and timing This is not suitable and flicker occurs.

In order to improve this, when the shutter speed is faster than the preset shutter speed threshold (1/100 second), the pixel clock signal is automatically adjusted to match the horizontal synchronization signal H_Sync to improve the flicker phenomenon.

4 (a) is a diagram illustrating a state in which the pixel clock signal and the horizontal synchronization signal are not synchronized due to a faster shutter speed. In the present invention, when the shutter speed increases above a threshold, the pixel clock signal as shown in FIG. By controlling the length of the blank period to be synchronized with the horizontal synchronization signal, it is possible to improve the flicker phenomenon in the image.

In the above description of the present invention, specific embodiments have been described, but various modifications may be made without departing from the scope of the present invention. Therefore, the scope of the present invention is not to be determined by the embodiments described above, but will be apparent in the claims as well as equivalent scope.

FIG. 1 is a graph illustrating a flicker generation period due to an illuminance level and a change cycle of a fluorescent lamp and a shutter speed cycle mismatch according to the illumination level.

2 is a block diagram of an image photographing apparatus for reducing flicker according to an exemplary embodiment of the present invention.

3 is a flowchart illustrating a process of reducing flicker according to an exemplary embodiment of the present invention.

4 is a diagram illustrating a pixel clock signal and a horizontal synchronization signal.

* Description of the symbols for the main parts of the drawings *

10: video signal processor 20: lens driving driver

30: winning part 40: A / D converter

Claims (4)

Setting a shutter speed at a high speed when light of illuminance higher than an illuminance threshold is incident; If the shutter speed is faster than a preset shutter speed threshold, adjusting a pixel clock signal, which is an image frame output clock, to synchronize the horizontal clock signal; Flicker reduction method comprising a. The method of claim 1, wherein the illuminance threshold is 1,500 Lux. 2. The method of claim 1, wherein the shutter speed threshold is 1/100 second. The method of claim 1, wherein adjusting the pixel clock signal increases the blank period of the pixel clock signal to synchronize the horizontal clock signal.

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