JPH06245171A - Video level limiter - Google Patents

Abstract

PURPOSE:To minimize the information quantity to be lost by limiting the level in response to the content of a video signal. CONSTITUTION:A memory 1 stores an input digital video signal S1 in a frame period or a field period. A histogram processing block 2 forms a histogram from a gradation distribution of signals stored in the memory 1 at every frame period or field period. A discrimination section 3 discriminates the gradation distribution subjected to histogram processing at every frame period or field. An arithmetic operation section 4 calculates an input output conversion parameter S2 based on discrimination data by the discrimination section 3. An input conversion section 5 writes lots of conversion characteristics corresponding to the parameter S2 is advance and converts the video signal from the memory 1 with the conversion characteristic determined by the parameter S2 from the arithmetic operation section 4. Thus, A converted signal is outputted from the input output conversion section 5 and a level is limited in response to the signal gradation distribution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, when displaying an image on a display panel such as a plasma display or a cathode ray tube, when the level of the video signal input to the display panel or the like is excessive, the level of the signal content is increased. The present invention relates to a video level limiting device that limits a video level according to a tonal distribution.

[0002]

2. Description of the Related Art When an image is displayed on a display panel such as a plasma display or a cathode ray tube, the level of an input signal exceeds a certain level in order to prevent deterioration of image quality due to excessive input and to protect a circuit. Are being treated to limit FIGS. 3 (A) and 3 (B) are principle configuration diagrams showing a conventional method of limiting the image level, and FIG. 3 (A) is a cathode ray tube (CRT) system,
(B) is the case of the panel display system. In the case of (A), a high voltage is applied to the anode of the cathode ray tube 31 by a flyback transformer (FBT32), and the anode current flows. In this case, the image processing circuit 34 is controlled to limit the image level to the cathode ray tube 31, which is a method generally called ABL or ACL. On the other hand, in the case of FIG. 3B, there is no such anode current as described above, and the display panel 35
The signal form supplied to the CRT system is an analog signal, whereas the panel display system is a digital video signal. That is, it is a digital process in which the input video signal is supplied to the display panel 35 via the pulse control circuit 36 and the drive circuit 37. Therefore, in the case of the panel display method, as shown in the figure, the power consumption at the time of supplying power to the drive circuit 37 and the like is detected (power consumption detection circuit 38), and when the power consumption increases above a predetermined level, The power consumption detection circuit 38 controls the pulse control circuit 36 to limit the number of pulses applied to the display panel 35.

[0003]

In the explanation of FIG. 3 described above, since the number of pulses is limited particularly in the case of FIG. B (panel display), a peak cutter is used for signals of any content. It has a drawback that the cotrust is cut at a certain level or higher, resulting in an unnatural image. In addition, there is a drawback that the gradation expression of the image is impaired even if the ACL is applied on the image circuit side. SUMMARY OF THE INVENTION It is an object of the present invention to provide a video level limiting device which improves the above-mentioned drawbacks in a display panel system and which can be applied to a cathode ray tube display system.

[0004]

According to the present invention, there is provided a memory for storing a digital video signal in a predetermined cycle, a means for converting a gradation distribution of a signal stored in the memory into a histogram in the predetermined cycle, and the histogram. Means for discriminating the gradation distribution for each predetermined period, means for computing an input / output conversion parameter based on the data by the discrimination means, and an input video signal from the memory based on the input / output conversion parameter by the computing means. The present invention provides a video level limiting device including input / output converting means for converting and outputting a desired signal.

[0005]

The digital video signal is temporarily stored in the frame cycle or the field cycle. The stored video signal is histogrammed with respect to the gradation distribution for each frame cycle or field cycle, and the gradation distribution is discriminated. An input / output conversion parameter is calculated from this determination, and the level of the input video signal is limited by ABL, ACL, or peak cut based on the calculated parameter.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image level limiting device according to the present invention will be described below with reference to the drawings. 1 is a block diagram of a main part showing an embodiment of a video level limiting device according to the present invention, and FIG. 2 is an explanatory diagram of FIG. 1 showing a histogram of a video signal, a level limiting method and the like. In FIG. 1, reference numeral 1 is a memory for storing the input digital video signal S1 in a frame cycle or field cycle, 2 is a block for histogram-producing the gradation distribution of the signal stored in the memory 1 for each frame cycle or field cycle, and 3 is a The discrimination unit 4 for discriminating the frame period or the gradation distribution for each field formed in the histogram, the arithmetic unit 4 for computing the input / output conversion parameter S2 on the basis of the discrimination data by the discrimination unit 3, and the reference numeral 5 are inputted from the memory 1. The input / output conversion unit converts the video signal into a desired signal based on the input / output conversion parameter S2 by the arithmetic unit 4 and outputs the signal.

Next, the operation of the present invention will be described. Or a frame cycle stored in the memory 1, or field period and either the signal aspects or interlace signal, or other means that the non-interlace signal or, be determined by considering the relationship between the accuracy of the histogram of the signal Is. As a matter of course, since the frame period increases as the amount of information, the accuracy of the gradation distribution of the histogram-generated video signal is improved. Here, the gradation means each gradation from white to black in the video signal. As described above, the video signal stored in the memory 1 is read out and the video signal for each frame cycle or field cycle (hereinafter, referred to as “predetermined cycle”) corresponding to the cycle at the time of storage is made into a histogram (histogram conversion). Block 2). The histogram in the present invention represents the distribution amount (number) of the image component of each gradation (described above) within a predetermined period for each gradation. An example of a histogram is shown in FIGS. 2 (A) and 2 (B).
It is each (a) figure of (C).

The horizontal axis of the figure represents the gradation of the image, the right end is white,
The left end is black, and the vertical axis represents the distribution amount included in the predetermined period of each gradation. And, in (A) and (A), the distribution from black to white is uniform, and in (B) and (A), the distribution is concentrated on the white side (the side with high brightness), (C). The figure (a) shows the case where the concentration is concentrated on the black side (the side where the brightness is dark) of the distribution opposite to that of the figure (B). In this way, the state in which the image signal is converted into a histogram is determined by the determination unit 3 as to whether the state is an image having the tendency shown in each of (A), (B) and (C). For example, the following method can be used for the above determination. In each of (A), (B), and (C) of FIG. 9, it is obtained by obtaining the upper threshold value and the lower threshold value with respect to the reference threshold value (vertical axis) k. When the threshold level is concentrated in the lower part, it is (B) (a), and when it is concentrated in the upper part, it is (C) (a). Other than that, it is (A). At this time, the characteristic curve is generally determined by calculating the average level of the signal and using it as a parameter. The data related to the above determination result is sent to the calculation unit 4. The calculation unit 4 calculates a parameter of how to limit the video signal based on the data from the determination unit 3. This operation result is the input / output conversion parameter
It is sent to the input / output conversion unit 5 as S2.

The input / output conversion unit 5 is specifically a ROM, and has a large number of conversion characteristics previously set to the input / output conversion parameter S2.
It is to be written corresponding to. That is, the video signal from the memory 1 is converted by the conversion characteristic determined by the input / output conversion parameter S2 from the arithmetic unit 4. A basic example of input / output conversion characteristics in the input / output conversion unit 5 is shown in FIG.
It shows in each (B) figure of (B) and (C). In the figure, the horizontal axis represents the gradation from black to white as in the case of (a) (as described above), and the vertical axis represents the level. And each of (a), (b) in FIGS. (A), (B), and (C) corresponds. Here, FIGS. (A) and (B) show a so-called ACL operation for limiting the contrast,
This is effective for level limitation when the distribution of each gradation is uniform (a), and FIGS.
The operation is a level limitation when the distribution of each gradation is concentrated on the white side (a), and the operation of cutting only the white peaks in FIGS. It is effective for each level limit when concentrated on the side. Cs in each figure (b) represents the characteristics when there is no limitation, Ca, C
b and Cc represent the characteristics of the above restrictions.

The conversion characteristic stored in the input / output conversion unit 5 (ROM) does not mean that each of Ca, Cb, and Cc is (b) in the figure, but the symbols αa, αb, and αc in the figure are different. This means that multiple conversion characteristics Ca, Cb, and Cc are written. Therefore, the arithmetic operation in the arithmetic unit 4 is an arithmetic operation for obtaining a parameter indicating which of the plurality of conversion characteristics is to be used. In this way, the converted signal is output from the input / output conversion unit 5, and the level is limited according to the gradation distribution of the signal.

[0011]

As described above, according to the present invention, the level is limited by either ACL, ABL, or white peak cut according to the content of the video signal. can do. In particular, the disadvantage that the amount of information is lost more than necessary by uniformly limiting the level as in the past is improved, and the amount of lost information can be minimized.

[Brief description of drawings]

FIG. 1 is a block diagram of essential parts showing an embodiment of a video level limiting device according to the present invention.

FIG. 2 is a diagram for explaining the operation of FIG.

FIG. 3 is a principal block diagram showing an example of a conventional video level limiting device.

[Explanation of symbols]

 1 Memory 2 Histogram Block 3 Discrimination Unit 4 Computing Unit 5 Input / Output Converter S1 Digital Video Signal S2 Input / Output Conversion Parameter

Claims (1)

[Claims] 1. A memory for storing a digital video signal for each predetermined cycle, a means for histogram-forming a gradation distribution of the signal stored in the memory for each predetermined cycle, and a gradation for the histogram for each predetermined cycle. Means for discriminating the distribution, means for computing the input / output conversion parameter based on the data by the discrimination means, and converting the input video signal from the memory into a desired signal based on the input / output conversion parameter by the computing means and outputting the signal. And an input / output conversion means for controlling the video level limiting device.