KR20000051454A - Gamma correction method of video camera - Google Patents

Abstract

PURPOSE: A gamma compensation method for a video camera is provided to adjust the gamma compensation amount according to the condition of light when one color object is present on a screen. CONSTITUTION: A gamma compensation method for a video camera includes first and second steps. At the first step(S700), whether the object is one color object or not is determined. At the second step(S720), one of the gamma compensation amounts is selected according to the light condition and the gamma compensation is performed using the selected gamma compensation amount when the object is determined to be a one color object. The first step further includes the step of calculating the variation of brightness signal of the screen, a step of comparing the variation calculated with a predetermined threshold value, and a step of determining the object as one color object when the variation is smaller than the predetermined threshold value.

Description

Gamma correction method of video camera

The present invention relates to gamma correction of a video camera, and more particularly, to a gamma correction method of adjusting a gamma correction value according to an illumination condition when a monochromatic subject is present on a screen.

The imaging characteristics of the video camera depend on the photoelectric conversion characteristics of the charge coupled device (CCD). That is, the magnitude of the optical signal from the subject and the magnitude of the photoelectrically converted signal are not in proportional relationship because the photoelectric conversion characteristic of the CCD is nonlinear. Accordingly, the video camera performs a process of correcting the nonlinear photoelectric conversion characteristic of the CCD, which is called gamma correction.

1 is a graph showing gamma correction characteristics. In a video camera, the photoelectric conversion characteristics of the CCD are corrected using the nonlinear amplification characteristics as shown in FIG.

Gamma correction characteristic adjusts the input signal level Output signal level When

It can be represented by.

Where K is the proportionality constant Is the gamma index of the CCD.

As shown in FIG. 1, the amplification degree drops sharply with reference to A and B, resulting in a click of a portion below the A portion and more than the B portion.

In a conventional video camera, gamma correction by a fixed gamma index is performed. Accordingly, when a dark or light monochromatic subject is present on the screen, it is difficult to identify the subject.

In other words, in the case of a dark monochromatic subject, when the lighting condition is dark, it is easy to be distributed in the portion A or below, and it becomes difficult to identify the subject on the screen. In addition, in the case of a light-colored monochromatic subject, when the lighting condition is bright, it is easy to be distributed in the B portion or more, and it is also difficult to identify.

Accordingly, when a monochromatic subject exists on the screen, the gamma correction value needs to be properly corrected according to the lighting conditions to make it easier to identify the monochromatic subject on the screen.

SUMMARY OF THE INVENTION An object of the present invention is to provide an improved gamma correction method for adjusting a gamma correction amount according to an illumination condition when a monochromatic subject exists on a screen as designed to meet the above requirements.

1 is a graph for schematically showing gamma correction.

2 is a flowchart illustrating a method of discriminating a monochromatic subject in the present invention.

3A to 3B are diagrams for illustrating an example of a subject area in the flowchart shown in FIG. 2.

4 is a diagram schematically illustrating a method of extracting an area excluding a peripheral part of a screen.

FIG. 5 is a flowchart illustrating an example of determining whether a monochromatic subject is the target of the region illustrated in FIG. 4.

6 is a block diagram showing the configuration of an apparatus for performing the method shown in FIG.

7 is a flowchart illustrating a gamma correction method according to the present invention.

8 is a block diagram showing the configuration of a video camera performing a gamma correction method according to the present invention.

A gamma correction method according to the present invention for achieving the above object comprises the steps of determining whether or not a monochrome object; In the case of a monochromatic subject as a result of the determination process, the method includes selecting one of gamma correction values prepared according to an illumination condition and performing gamma correction.

Here, the determining of the presence or absence of the monochromatic subject may include calculating a scatter diagram of the luminance signal on the screen photographing the subject; Comparing the scatter diagram with a predetermined threshold; And determining that the scattered object is smaller than a predetermined threshold as a result of the comparing process as a monochromatic subject. Hereinafter, the configuration and operation of the present invention will be described in detail with reference to the accompanying drawings.

2 is a flowchart illustrating a method of discriminating a monochromatic subject in the present invention. In the monochromatic determination method according to the present invention, a scatter diagram of a luminance signal is obtained in a subject area, and whether or not a monochromatic subject is determined based on the size of the scatter diagram obtained. Specifically, if the scatter of the luminance signal is smaller than the predetermined threshold, it is discriminated as a monochromatic subject. Here, as the threshold value, the average value of the luminance signals in the subject area is used.

Scatter Is calculated as mean deviation, standard deviation, etc.

Average deviation And standard deviation Means that the pixel And the average value of the luminance signal in the subject area. This

,

Standard Deviation Is

Appears.

Here, n is the number of pixels in the subject area.

In the method illustrated in FIG. 2, first, an average value of luminance signals is obtained in a subject area (S200). Here, the subject area is exactly an area occupied by the subject, but may be an area including the subject. The subject area is determined by contour extraction. The method of using an area including a subject is simple, and an area excluding a peripheral part is used on the screen. In most cases, since the subject is located near the center of the screen, an area including the subject may be approximated by excluding a peripheral portion.

First, an average value of luminance signals in a subject area is obtained (S200).

The scatter diagram of the luminance signal in the subject area is obtained (S210).

The average value of the luminance signal obtained in S200 is compared with the scatter diagram of the luminance signal obtained in S210.

If the scattering degree of the luminance signal is smaller than a predetermined threshold, for example, the average value of the luminance signal, it is discriminated as a monochromatic subject (S230).

3A to 3B are diagrams for illustrating an example of a subject area in the flowchart shown in FIG. 2. FIG. 3A shows an example of an area (hatched portion) 300 occupied by the subject, and FIG. 3B shows an example of an area (hatched portion 310) including the subject 320. The example shown in FIG. 3A is set by extracting an outline of a subject and extracting an area included in the outline. The example shown in FIG. 3B is set by extracting an area except for the periphery of the screen.

4 is a diagram schematically illustrating a method of extracting an area excluding a peripheral part of a screen. As illustrated in FIG. 4, 64 sub-screens in which the entire screen 200 is divided evenly ( To ) And an area (except sub screens of the peripheral part) among the divided sub screens ( To ).

FIG. 5 is a flowchart illustrating an example of determining whether a monochromatic subject is the target of the region illustrated in FIG. 4.

First, block To Average value of luminance signal at Calculate the (S500).

To Scatter plot of the luminance signal at In operation S510, a block having a value out of a predetermined range may be excluded.

Average value of luminance signal obtained in S500 Scattering Diagram of Luminance Signals Obtained from S510 Compare to (S520).

end If smaller, it is determined as a monochromatic subject.

6 is a block diagram showing the configuration of an apparatus for performing the method shown in FIG. The apparatus illustrated in FIG. 6 includes a block divider 60, an average value calculator 62 for each block, an average value calculator 64, a scatter plot calculator 66, and a comparator 68.

The block divider 60 divides an input video signal into blocks and outputs the divided video signals. This block divider 60 may be implemented by a frame memory and an address generator. The frame memory stores the input video signal in units of frames. The address generator divides the video signal stored in the frame memory according to the block section and sequentially outputs the divided sub blocks. At this time, the peripheral subblocks are not output.

The average value calculator 62 for each block calculates an average value of luminance signals of sub-blocks sequentially output from the block divider 60.

The average calculator 64 and the scatter plot calculator 66 calculate the average value and the scatter plot of each screen unit from the average values of the luminance signals for each block output from the average block calculator 62.

The comparator 68 compares the average value provided by the average value calculator 64 with the scatter plot provided by the scatter plot calculator 66. The comparison determination result of the comparator 68 indicates whether or not it is a monochromatic subject. That is, if the scatter is smaller than the average value, the comparator 68 outputs a "high" signal indicating that the monochrome object.

7 is a flowchart illustrating a gamma correction method according to the present invention. The method illustrated in FIG. 7 selects one of gamma correction values prepared according to an illumination condition according to whether or not a monochrome object is used to perform gamma correction.

First, it is determined whether or not the subject is a monochromatic subject. (S700) Whether or not the subject is a monochromatic subject is determined by the method shown in FIG. 2 and the apparatus shown in FIG. In other words, if the scatter of the luminance signal of the subject is smaller than the predetermined threshold, it is determined as a monochromatic subject. The concept of a monochromatic subject includes a white subject.

If it is determined in S700 that it is not a monochromatic subject, normal gamma correction is performed (S710). That is, gamma correction is performed according to the gamma index of the CCD.

If it is determined in S700 to be a monochromatic subject, the lighting condition is determined (S720).

The gamma correction amount is adjusted by selecting one of the adjustment values prepared according to the lighting conditions. Illumination conditions are determined by the degree of opening of the camera aperture. Since the aperture of the camera is closed as the light is brighter and opened as the light is dark, the illumination state can be determined by determining the degree of opening of the aperture.

That is, when the aperture of the iris is above a predetermined threshold, it is determined by outdoor sunlight conditions, and the amplification degree of the bright part is adjusted less than that of normal gamma correction (S730). The amplification degree of the portion is adjusted to be larger than during normal gamma correction (S740).

The opening degree of the iris is detected by the Hall element attached to the lens. Hall elements detect magnetic force as the aperture opens and closes, outputting them as voltage values, and are commonly used in video cameras. In outdoor conditions, since the state is brighter than indoors, the aperture is closed and the hall value is lowered.

According to the monochromatic subject discriminating method of the present invention, a white subject is also identified as a monochromatic subject. In the case of a white subject, it is correct to perform normal white balance adjustment to the target, but since the prepared white balance adjustment values are set in a state of capturing the white subject, an approximate value can also be obtained by the white balance adjustment method of the present invention.

8 is a block diagram showing the configuration of a video camera for performing the white balance adjustment method according to the present invention. 8 includes a lens unit 80, a charge coupled device 82, a dual correlation sampling unit 84, an A / D conversion unit 86, a signal processing unit 88, and a microprocessor. 90, an automatic gain control unit 92, a shutter control unit 94, a timing generator 96, an aperture driver 98, an aperture control unit 100, and a hall detector 102.

Here, the shutter controller 94 controls the shutter timing by soft operation. Specifically, the shutter timing is controlled by adjusting the read timing of the solid-state imaging device 82 through the timing generator 96.

The gamma correction operation is performed by the signal processor 88, the microprocessor 90, the automatic gain adjuster 92, and the hall detector 102.

In performing the gamma correction operation according to the present invention, the signal processor 88 calculates an average luminance value and a scatter diagram of an area including a subject on a screen. The microprocessor 90 compares the average luminance value provided by the signal processor 88 with the scatter diagram to determine whether the monochrome object is a monochromatic subject.

Normal gamma correction is performed when the object is not a monochromatic object, that is, when the scatter is equal to or larger than the average luminance value. In performing a normal gamma correction operation, the signal processor 88 performs gamma correction according to a gamma index given by a CCD.

In the case of a monochromatic subject, that is, when the scatter is smaller than the average luminance value, one of the pre-stored gamma correction values is selected and output. Here, the pre-stored gamma correction values refer to gamma correction values experimentally obtained in typical lighting conditions. Representative lighting states may be outdoor solar lighting conditions or indoor incandescent bulb lighting conditions.

The selection criterion for selecting one of the prepared gamma adjustments is the open state of the iris. The aperture is closed as the amount of incident light increases. That is, the outdoor solar lighting conditions are more open than the indoor incandescent bulb lighting conditions. The boundary value between these two conditions is experimentally determined and the indoor and outdoor conditions are distinguished from the obtained experimental values. In the example of the present invention, the value detected by the hall detector 102 is " 8 " which is the middle value of the detection range. However, this threshold may vary depending on the device.

When the value detected by the hall detector 102 is equal to or larger than "8", it is determined that the solar lighting condition is outdoors, and corresponding gamma correction values are applied to the automatic gain control unit 92.

If the value detected by the hall detector 102 is smaller than " 8 ", it is determined that it is an indoor incandescent bulb lighting condition, and corresponding gamma correction values are applied to the automatic gain control unit 92.

Through such an operation, when the device illustrated in FIG. 6 is determined to be a monochromatic subject, the apparatus outputs a gamma correction value for each illumination condition prepared in advance without performing a normal gamma correction operation.

As described above, the gamma correction method according to the present invention has the effect of expanding the dynamic range of the subject by selecting and adjusting one of the gamma correction values set according to an illumination condition in the case of a monochromatic subject.

Claims (5)

In the gamma correction method of the video camera, Determining whether a monochromatic subject is present; And a gamma correction by selecting one of gamma correction values prepared according to an illumination condition when the object is a monochrome object as a result of the determination process. The method of claim 1, wherein the determining of the monochrome subject Calculating a scatter diagram of a luminance signal on a screen of photographing a subject; Comparing the scatter diagram with a predetermined threshold; And And determining that the scattered object is smaller than a predetermined threshold as a result of the comparing process as a monochromatic subject. The gamma correction method of claim 2, wherein the scattering calculation step is performed on a luminance signal of an area occupied by a subject. The gamma correction method of claim 2, wherein the scattering calculation process is performed on a luminance signal of an area including a subject and a peripheral portion of the screen is excluded. The gamma correction method of claim 2, wherein the threshold value is an average value of luminance signals in a region considered in the scatter diagram calculation process.