KR100503471B1 - B/W signal stretch control apparatus and method - Google Patents

Abstract

The present invention relates to a black / white signal region extension adjusting device and method for extending a black signal region and / or a white signal region in order to express the input signal level at all output levels. The black / white stretch adjusting device according to the present invention includes a scene change detector for determining whether a scene is changed, a minimum / maximum signal detector for extracting a maximum and / or minimum level signal of an input signal, a tilt value and a stretch for determining an area to be stretched. A tilt / tilt calculating unit for determining a tilt of an area to be used, a tilt determining unit for adjusting a tilt change according to whether a screen is changed, and a mapping unit for mapping using a mapping function having a tilt determined by the tilt determining unit. . According to the present invention, when the scene does not change, flutter of the screen due to local scene change can be prevented, and when the scene changes, the stretch intensity can be quickly changed to achieve black / white signal region extension.

Description

B / W signal stretch control apparatus and method according to scene change

The present invention relates to a black / white stretch adjusting device and method for expanding a black signal output level and / or a white signal output level when a level of an input video signal has a range smaller than an outputable level in a general video display device. will be.

Advances in optical technology and electronics have led to the development of modern image display devices using reflective display elements such as digital light processing (DLP) as well as TVs implemented in CRT (Crown Tube) and LCD (Liquid Crystal Display) systems. The latest hardware equipment has been well received by consumers by displaying images in high definition and high definition image quality.

However, a general video signal input to the video display device may have a smaller signal range than the hardware can handle. In this case, no matter how new the hardware, the output is limited. As one of several methods for solving such a problem, a black / white stretch technique may be used. The black / white stretch technique may be applied to a representation region of an output device when the representation region of an input image is small. It is a method to increase the contrast of the screen by stretching it closely. Even if the input signal region is the same as the output region, it can be used as a method of improving the contrast by selectively darkening the black region.

Figure 1 shows a simple block diagram of the structure of the black / white stretching device according to the prior art. Referring to FIG. 1, a commonly used black / white stretching method is described. First, an applied input signal first filters noise through a low pass filter (LPF).

When passing through the LPF 10, the minimum / maximum level signal detector 20 detects a signal having a minimum level and a signal having a maximum level among the input signals. The minimum / maximum level signal is for obtaining a mapping function used in a mapping step to be described later.

When the minimum / maximum level signal is detected, the tilt determination unit 30 determines a tilt value for determining a signal region to be extended.

The slope calculator 40 calculates a new mapping slope in which the output level is increased with respect to the region determined by the tilt value. The mapping slope refers to the slope of the mapping function necessary for mapping the output signal according to the input signal by the mapping unit 50.

The mapping unit 50 maps an output signal by using a mapping function having a new mapping slope calculated by the slope calculating unit 40, and as a result, may be expressed in the entire level region that can be output.

2 shows a graph of the mapping function used for the black / white stretching method. FIG. 2 shows an example of a mapping function in a state where the mapping slope is 1 and the input signal is limited to a level region of 10 to 245. FIG. Since the mapping slope is 1, the input level signal is converted into the output level signal as it is, and the output is also limited within the signal level range of 10 to 245. In order to express the output signal in the entire region, the black / white region should be stretched to 0 to 255 levels. First, the tilt 1 and tilt 2 values for determining the black signal stretching region and the white signal stretching region are determined. . The area | region below the said tilt 1 value and the area | region above the said tilt 2 value become a black / white extension area | region, respectively.

In the above example, since the black signal region and the white signal region are extended at the same time, two tilt values (tilt 1 and tilt 2) are determined. If only the black signal region is to be extended, only one tilt value is used. You decide.

Once the tilt value is determined, the process of computing the mapping slope of the stretched area is developed. That is, the mapping slope of the black stretched area is calculated by connecting the point having the output level 0 (that is, the input signal level 10 and the output signal level 0) at the min value and the point corresponding to the tilt 1 value, and the output level at the max value. The mapping slope of the white stretched region is calculated by connecting the point having 245 (that is, the input signal level 245 and the output signal level 255) and the point corresponding to the tilt 2 value. As a result, it is possible to determine a mapping function having a slope of 1 in the interval between the tilt 1 and the tilt 2 and having a newly calculated slope in the region below the tilt 1 and the region above the tilt 2, by mapping using the mapping function. The black / white signal area is stretched.

On the other hand, when the black / white signal region is extended, the minimum / maximum level signal of the input signal may change even when the partial screen is changed, thereby causing flutter of the screen. That is, referring to the black signal region in FIG. 2, the mapping slope suddenly changes due to a sudden change in the min value, resulting in a phenomenon that the black / white stretched region becomes brighter and darker on the screen. do.

According to the prior art, the change of the mapping function is controlled by using the LPF in order to reduce the effect of the sudden scene change. However, when using the LPF to control the hardware burden is more, and there is a problem that the change in elongation strength is not made quickly when switching the screen.

An object of the present invention is to provide an apparatus and method for extending a black / white signal region by determining a scene change and adjusting a slope change rate of a mapping function according to the determination result. .

The black / white stretch adjustment device according to the present invention is a scene change detection unit for determining whether the scene change by comparing the previous frame and the current frame, when it is determined that the scene change, detecting the minimum level signal and the maximum level signal of the input signal A tilt / tilt calculator for determining a tilt value for each output level extension and calculating a mapping slope of the extension region with respect to the minimum / maximum signal detector, the minimum level signal and the maximum level signal detected by the minimum / maximum signal detector; By applying an input signal to a mapping function having a slope determination unit and an output signal mapping slope to determine an output signal mapping slope according to a scene change, by using the mapping slope of the current frame and the previous frame determined by the slope / tilt calculation unit. It characterized in that it comprises a mapping unit for mapping.

On the other hand, the black / white stretch adjustment method according to the present invention, comparing the previous frame and the current frame to detect whether the scene has changed, if detected as a scene change, outputting the scene change signal to the slope determination unit, input Detecting a minimum level signal and / or a maximum level signal by calculating a signal level, calculating a tilt value for determining a black signal area and / or a white signal area to be expanded among the input signals, and calculating a mapping slope of the area to be expanded The method may include determining an output signal mapping slope according to a scene change by using the calculated slope of the stretched region, and mapping the mapping signal according to a mapping function having the output signal mapping slope.

Hereinafter, an apparatus and method for adjusting black / white signal region extension according to the present invention will be described with reference to the accompanying drawings.

Figure 3 is a block diagram showing the configuration of the black / white stretch adjusting device according to the present invention.

Referring to the drawings, when the scene change detection unit 110 compares the previous frame and the current frame with respect to the applied input signal, it is determined whether the scene has changed, and if it is determined that the scene has changed, the slope determination unit 140 Will be printed.

To determine whether the scene changes, first, the previous frame is divided into a predetermined number of blocks, and image characteristic values are extracted for each block. The image characteristic value means a numerical value that can be characteristic for the image of the block. Typically, the average value of the signal level in each block can be used, but other characteristic values can be used in addition to the calculated data such as the average value. Next, the current frame is divided into blocks equal to the number of blocks divided by the previous frame, and an image characteristic value is obtained for each block. Next, the image characteristic values are compared for each of the contrasting blocks of the previous frame and the current frame.

4 illustrates a process of dividing and comparing blocks with respect to a previous frame and a current frame to determine whether the scene has changed. According to Fig. 4, each block A1, B1, C1, .... of frame 1 and each block A2, B2, C3, .... of frame 2 can be compared.

The number of blocks of which the image characteristic value has changed among the compared blocks is checked, and it is checked whether the number exceeds the predetermined number. When the number of blocks whose image characteristic values are changed exceeds a predetermined number set by the user, the scene change detector 110 determines that the scene has changed, and outputs a scene change signal to the tilt determination unit 140. If the caption or caption image appears intermittently only on a certain portion of the screen without changing the entire screen, if the changed number of blocks is less than or equal to the number set by the user, the scene change is not determined.

Meanwhile, the minimum / maximum signal detector (or MIN / MAX detector 120) detects the minimum level signal and the maximum level signal among the input signal levels.

Next, the slope / tilt calculating unit (or SLOPE / TILT calculating unit 130) calculates a slope of the mapping function to be used for mapping, while tilting a tilt value that defines an area to be extended with respect to the black / white signal level. Will be decided. The method for calculating the slope is the same as in the above-described prior art. That is, if the image display apparatus can express 0 to 255 levels, the mapping slope of the black signal extension region is obtained so that the output level is mapped to 0 at the minimum input level, and the white signal is mapped to 255 at the maximum input level. The mapping slope of the stretched region is obtained.

Meanwhile, the slope / tilt calculator 130 estimates the size of the region where black / white stretching is to be performed based on the minimum signal level and the maximum signal level input from the minimum / maximum signal detector 120. In addition, it also plays a role of adjusting the tilt value to determine the stretched region.

Next, the slope determination unit 140 determines the slope of the mapping function using the mapping slope of the frame calculated by the slope / tilt calculator 130. The slope determiner 140 may be implemented using an infinite impulse response (IRR) filter. The IIR filter is a type of digital filter, and the filtering is performed by recursively applying the value of the input signal and the value of the output signal. The gradient determiner 140 may adjust the response speed of the gradient change according to the scene change by applying the mapping slope of the previous frame and the mapping slope of the current frame to the IIR filter.

That is, in a situation where the scene is not changing, the change of the slope is adjusted by more reflecting the slope of the previous frame in the output signal mapping slope determination, and the scene change detection unit 110 determines that the scene change signal is determined as the scene change. When sent, the slope is determined to reflect more of the slope of the current frame. Since the average value of a certain number of blocks changes when the subtitle passes or the caption image is displayed while the entire screen is not changed, the entire scene is determined not to change, and the mapping slope of the previous frame is maintained. While the flutter can be prevented, the scene changes, allowing you to quickly change the stretch intensity to reflect the slope of the current frame as much as possible. In this way, it is possible to increase the black / white signal region while adjusting the rate of change of the slope according to whether or not the scene changes, thereby preventing flutter of the screen.

The slope determination unit 140 implemented using the IIR filter determines the output signal mapping slope through the formula of So = k * (So_curr) + (1-k) * (So_prev). Denotes the output mapping slope, So_curr denotes the output mapping slope of the current frame, and So_prev denotes the output mapping slope of the previous frame.

K in the equation is an arbitrary variable, and the slope may be determined by adjusting k according to whether or not the scene changes. That is, when the scene change signal is input from the scene change detector 110, the k value is set to a value larger than 1-k. Therefore, the output mapping slope So is determined to be close to the output mapping slope of the current frame. Meanwhile, while the scene change signal is not input, the k value is set to a value smaller than 1-k to determine the output mapping slope while maintaining the output mapping slope of the previous frame substantially.

When the output mapping slope is determined, the mapping unit 150 maps the output function using a mapping function having the slope with respect to the input signal. In the absence of a scene change, black and white stretching is performed by mapping the mapping function while maintaining the inclination of the mapping function almost unchanged. If there is a scene change, the mapping function is mapped according to the mapping function determined by quickly reflecting the slope of the current frame.

Hereinafter, the black / white elongation adjustment method according to the present invention.

When the input signal comes in, first, the scene change detection unit 110 determines whether the scene changes. The determination method has been described above. If it is determined that the scene change, the scene change signal is sent to the slope determiner 140.

Meanwhile, the minimum / maximum signal detector 120 detects a signal having a minimum level and a signal having a maximum level among input signals.

Next, the tilt / tilt calculator 130 calculates the tilt and tilt values of the frame using the detected minimum level signal and the maximum level signal. On the other hand, if the black signal and the white signal region are not stretched at the same time but only the black signal or the white signal is stretched, the tilt and tilt values may be calculated only for any one of the minimum and maximum level signals. .

Next, the slope determiner 140 determines the slope of the mapping function using the slopes of the previous frame and the current frame calculated by the slope / tilt calculator 130. That is, in the absence of a scene change, the mapping function of the previous frame is almost used to determine the mapping function to prevent flutter of the screen. In the case of a scene change, the mapping slope of the current frame is reflected a lot. You will quickly change your stretch strength.

When the mapping function is determined by determining the mapping slope, the mapping according to the mapping function is performed to extend the black / white signal output region.

The foregoing detailed description of the invention has been presented for purposes of illustration and description, and is not intended to limit the invention thereto. In view of the above description, those skilled in the art can make improvements and modifications without departing from the spirit and scope of the present invention.

According to the present invention, even when the input signal level is limited to a certain range, the contrast of the screen can be extended by extending the black signal area and / or the white signal area. In particular, the rate of change of the mapping function is adjusted differently depending on whether the screen changes when the black / white signal region is extended, so that when the entire scene is unchanged, the minimum and / or maximum signal level may occur due to sudden caption appearance or caption image appearance. When the change is made, the change of the mapping inclination may be slowed to prevent flutter of the screen, and when the whole scene is changed, the mapping inclination may be quickly changed to increase the black / white signal region to fit the new screen.

1 is a simple block diagram of the configuration of the black / white stretch adjustment device according to the prior art,

2 is a mapping function graph used in the black / white stretch adjustment device

Figure 3 is a simple block diagram of the configuration of the black / white stretch adjusting device according to the present invention,

4 is a diagram showing a step of detecting a scene change in the black / white stretch adjusting device of the present invention.

Claims (9)

A scene change detection unit comparing the previous frame and the current frame to determine whether the scene has changed; A minimum / maximum signal detector for detecting a minimum level signal and / or a maximum level signal among input signals; A tilt / tilt calculator configured to determine a tilt value for determining the stretched region among the input signal regions, and calculate a mapping slope of the stretched region for each frame; A slope determiner configured to determine an output signal mapping slope according to whether the scene is changed by using the mapping slope of the stretched region; and And a mapping unit configured to apply and map an input signal to a mapping function having the output signal mapping slope. The method of claim 1, The scene change detection unit, After dividing the previous frame and the current frame into a plurality of blocks of the same number, the image characteristic values of each block are obtained and compared, and the number of blocks whose image characteristic values have changed is determined. A black / white stretch adjusting device according to a scene change, characterized by outputting a scene change signal to a tilt calculator. The method of claim 2, And the image characteristic value uses a level average value of a signal existing in each block. The method according to claim 1 or 2, The tilt determination unit, While the scene change signal is not input from the scene change detection unit, the output signal mapping slope of the stretched area is slowly changed, and when the scene change signal is input, the output signal mapping slope is rapidly changed. / Bag height adjustment device. The method according to claim 1 or 2, The slope determination unit determines the slope of the output signal mapping using the following equation, and the k value in the equation is set to a value greater than 1-k when the scene change signal is input, and 1 while the scene change signal is not input. Black and white height adjustment device according to the scene change characterized in that it is set to a value less than -k: So = k * (So_curr) + (1-k) * (So_prev) So is the output signal mapping slope, So_curr is the mapping slope of the current frame, So_prev is the mapping slope of the previous frame, and k is any variable. Comparing the previous frame with the current frame of the input signal and determining whether the scene has changed; Outputting a scene change signal to a tilt determiner when it is determined that the scene change; Checking the input signal level to detect a minimum level signal and / or a maximum level signal; Calculating a tilt value for determining a black signal region and / or a white signal region to be extended among the input signals and a mapping slope of the region to be expanded; Determining an output signal mapping slope using the mapping slope of the region to be stretched; and And mapping according to a mapping function having the output signal mapping slope. The method of claim 6, Detecting the scene change, Calculating an image characteristic value of each block by dividing a previous frame into a predetermined number of blocks; Calculating an image characteristic value of each block by dividing a current frame into blocks equal to the number of blocks of the previous frame; Comparing the blocks contrasted from the previous frame and the current frame to identify the number of blocks whose image characteristic values have changed; and And determining that the scene changes when the number of blocks whose image characteristic values are changed is greater than or equal to a predetermined number. The method according to claim 6 or 7, Determining the output signal mapping slope is determined using the following equation, The k value in the above equation is set to a value larger than 1-k when a scene change signal is input, and to a value smaller than 1-k while the scene change signal is not input. Height adjustment method: So = k * (So_curr) + (1-k) * (So_prev) So is the output signal mapping slope, So_curr is the mapping slope of the current frame, So_prev is the mapping slope of the previous frame, and k is any variable. The method of claim 7, wherein And the image characteristic value uses a level average value of a signal existing in each block.