CN100405430C - A driving control method for enhancing details of low gray value images - Google Patents

Abstract

A driving control method for enhancing details of low-gray-value images, which belongs to the technical field of plasma TV display, includes a basic circuit of a plasma display screen, an inverse gamma correction method, and a peak extraction circuit, The judging circuit and the delaying circuit constitute a special correction circuit for dynamic anti-γ correction. The judging circuit extracts the maximum gray value M in an image according to the peak value extraction circuit and selects a weight scheme to control the encoder and the pulse number processing circuit. , this dynamic anti-gamma correction method, the quantization bit width can be changed, which reduces the gray level loss of reproducing low gray value images, improves the layering of the image without reducing the brightness value, and improves the plasma TV display screen display screen.

Description

A driving control method for enhancing details of low gray value images

technical field

The invention belongs to the technical field of plasma television display, in particular to a drive control technology for enhancing the reproduction of low-gray-value image details by a PDP (Plasma Display Panel).

Background technique

Plasma TV is a flat-panel wall-mounted new TV that uses plasma display panel PDP as the display screen. An active light-emitting flat panel display device that emits visible light from red, green and blue (ie, RGB) tricolor photoluminescent phosphors. The main parameters of a color PDP include resolution, display capacity, brightness, contrast, gray scale, etc., among which the gray scale determines the number of colors. When the transmission characteristic of the TV system is linear, and the brightness Lo of the scene reproduced by the display system is proportional to the brightness Li of the original scene, the signal can be transmitted and the image can be reproduced without distortion. But in fact, due to the mutual conversion and transmission between photoelectric signals, the entire TV transmission system has nonlinear characteristics. There are three sources of nonlinearity: camera tube, transmission system and display device. Taking the current mainstream cathode ray tube (CRT) display device as an example, there is a nonlinear relationship between the brightness Lo of the reproduced scene and the electrical signal S that controls the light emission:

$\mathrm{<span\; class="notranslate">\; Lo</span>}<span\; class="notranslate">\; \&Proportional;</span>{\mathrm{<span\; class="notranslate">\; S</span>}}^{{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}$

γ ₂ is the pre-correction coefficient, which generally takes a value between 2.2 and 2.8. In order to keep the transmission characteristics of the entire TV system linear, pre-correction must be performed on the TV transmission system before the CRT. After pre-correction, the transmission characteristics of the entire TV system are :

$\mathrm{<span\; class="notranslate">\; Lo</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; k</span>}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}$

Among them, k is the proportional system, γ ₁ is the pre-correction coefficient, take 0.45, so that γ ₁ γ ₂ ≈ 1, the pre-corrected signal is transmitted to the CRT display device, and the transmission characteristics of the entire TV system, that is, Lo and Li have a linear relationship , so that the image can be reproduced without distortion.

Different from CRT, PDP is a digital display device, and its electro-optical conversion characteristics are linear, that is, γ ₂ = 1. PDP is used to directly replace CRT. In order to take into account CRT, grayscale pre-correction has been made in the transmission channel. If it is not for PDP photoelectric If the conversion characteristics are corrected for grayscale, then γ ₁ γ ₂ = 0.45, the transmission characteristics of the entire display system are nonlinear, and the reproduced image will produce serious grayscale loss and grayscale distortion.

Therefore, in the PDP, it is necessary to carry out gray scale correction for the pre-correction of the TV transmission system, which is called inverse gamma correction. Inverse gamma correction is a digital processing process, and the output digital image signal Vo has the following relationship with the input digital image signal Vi:

$\mathrm{<span\; class="notranslate">\; Vo</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; Vi</span>}}^{{\mathrm{<span\; class="notranslate">\; \&gamma;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}$

γ ₂ generally takes a value between 2.2 and 2.8, and Vi is an 8-bit digital signal. Taking γ ₂ =2.2 as an example, when 8-bit, 9-bit and 10-bit quantization are given in the table in Fig. 1, the digital signal Vo corresponding to the output in the range of Vi=0-67 low gray value, it can be seen that Vi For 8, 9, and 10-bit quantization, the gray-scale levels of Vo are reduced to 11, 21, and 39 respectively. It can be seen that gray-scale loss occurs in low-gray-value areas. The calculation shows that 8-bit Quantized grayscale loss is 84%, 9-bit quantized grayscale loss is 69%, 10-bit quantized grayscale loss is 43%, 11-bit quantized grayscale loss is 25%, and 12-bit quantized grayscale loss is 15%. The grayscale loss in the low grayscale value area leads to the reduction of the resolvable brightness levels in the grayscale area and the degradation of image quality. In order to improve the image quality, we should start to reduce the loss of gray scale, and increase the quantization bit width. However, reducing the loss of gray scale and improving the brightness of PDP are mutually contradictory.

It can also be seen from the table in Figure 1 that the minimum gray level difference of 8-bit quantization is 1, that is, the quantization precision is 1, the precision of 9-bit quantization is 0.5, and the precision of 10-bit quantization is 0.25, that is, the quantization bit width plus 1 , the quantization precision is equal to the precision before widening divided by 2.

For the PDP that adopts the sub-field display mode to realize the grayscale control, the increase of the bit width is at the cost of increasing the number of driven subfields and sacrificing the brightness, and reducing the loss of grayscale and improving the brightness of the PDP are contradictory.

Traditional inverse gamma correction uses a fixed quantization bit width. Considering the brightness of the PDP, the bit width should not be too large, which will cause serious gray level loss in the low gray value area of the reproduced image, and the image level will be poor. This contradiction awaits further resolution.

Contents of the invention

The technical problem to be solved by the present invention is that the calibration of the gray scale in the known technology is to adopt a fixed quantization bit width. Since the brightness of the PDP is taken into account, the bit width should not be too large, which will cause serious problems in the low gray scale area. Grayscale loss, in order to solve this contradiction technically and overcome the deficiencies in the prior art, it is necessary to re-adopt a grayscale calibration method to reduce the grayscale loss and maintain the brightness level without reducing the brightness value. The present invention The purpose of the present invention is to provide a driving control method for enhancing the details of low-gray-value images, which is achieved through the following technical solutions: a driving and controlling method for enhancing the details of low-gray-value images, including the basic Circuit, anti-gamma correction method, on the basis of the basic circuit, add a peak value extraction circuit, a judgment circuit and a delay circuit to form a special correction circuit, which is characterized in that, dynamic anti-gamma correction is carried out, and the number of Under the same situation, the quantization bit width value can be adaptively changed with the peak brightness of the reproduced image, so as to reduce the gray scale loss of the reproduced low gray value image, and the judgment circuit extracts a field image according to the peak value extraction circuit The size of the maximum gray value M in the selected weight scheme to control the encoder and the pulse number processing circuit, while selecting the quantization bit width to control the anti-gamma correction circuit; The signal of the correction circuit corresponds to the control signal calculated by the judgment circuit according to the field.

The peak extraction circuit in the special-purpose correction circuit is a comparator circuit, which compares the signals of adjacent pixels. The color PDP adopts the sub-field display mode to realize gray scale control, that is, a TV field (referred to as field for short) ) is divided into multiple sub-fields that emit light successively. To achieve 256-level grayscale display, at least 8 sub-fields with weights of 1-2-4-8-16-32-64-128 (binary code) are required. Through these 8 sub-fields Different combinations of fields are used to realize the gray level. For non-binary coding, more than 8 sub-fields are required to achieve 256-level gray-scale display. At this time, a repetitive code will appear, which optimizes the coding process. The number of emitted light pulses in each subfield is proportional to the weight of the subfield. Therefore, the subfield display mode actually realizes gray scale control by adjusting the number of light emitting pulses.

PDP generally uses 11 or 12 subfields to achieve grayscale control. Taking 12 subfields as an example, assume that the following weighting scheme is selected:

1-2-4-7-11-16-22-29-37-46-56-67

The sum of the weights is 298, so this scheme can express up to 299 gray levels (0-298), the sum of the weights of the first 11 subfields is 231, when the maximum gray value of the reproduced image is not greater than 231, the first 11 subfields are used The field is enough to encode the image data, that is, the weight 67 is not considered when encoding. Therefore, the weight 67 is changed to the weight 0.5, and the weight adjustment scheme is as follows:

0.5-1-2-4-7-11-16-22-29-37-46-56

There are still 12 subfields, the weight sum is 231.5, the minimum weight is 0.5, and the weight sum of the first 11 subfields is 175.5. When the maximum grayscale value of the reproduced image is not greater than 175, the first 11 subfields are enough to encode the image data, that is, the weight 56 is not considered when encoding, so change the weight 56 to 0.25, and adjust the weight scheme again as follows:

0.25-0.5-1-2-4-7-11-16-22-29-37-46

There are still 12 subfields, the weight sum is 175.75, and the minimum weight is 0.25. By analogy, the results are shown in the table in Figure 2.

Combined with inverse gamma correction, due to the loss of gray level in the low gray value area, the loss of gray level decreases with the increase of the quantization bit width. When the maximum grayscale value M of the reproduced image is greater than 231, generally speaking, the image is brighter and the low grayscale value area in the image is smaller, and the grayscale loss is not large even if 8-bit quantization is used for inverse gamma correction. Correspondingly, a weight scheme with a minimum weight of 1 is adopted; when the maximum gray value M of the reproduced image is between 175 and 231, the low gray value area in the image is moderate, and the inverse gamma correction adopts 9-bit quantization to reduce the loss of gray , at this time, the corresponding weight scheme with the minimum weight of 0.5 is adopted; when the maximum gray value M of the reproduced image is between 129 and 175, the low gray value area in the image is relatively large, and the inverse γ correction adopts 10-bit quantization, The gray level loss is further reduced. At this time, a weight scheme with a minimum weight of 0.25 is adopted accordingly; and so on, the results are shown in the table in Figure 3. It can be seen that the present invention adaptively selects the quantization bit width of inverse gamma correction according to the size of the low gray value area of the reproduced image, so as to improve the image quality of the low gray area. The beneficial effect of the present invention is that the quantization bit width can be changed in this dynamic reverse gamma correction method, which reduces the grayscale loss of reproducing low grayscale value images, improves the layering of the image without reducing the brightness value, and improves displayed on the plasma TV display.

Description of drawings

Figure 1 is the inverse gamma correction chart of the 8-bit, 9-bit, and 10-bit quantization bit width in the low gray value area

Figure 2 is a diagram of the weight selection scheme

Figure 3 is a chart of the relationship between the maximum gray value M and the minimum weight and quantization bit width

Fig. 4 is a block schematic diagram of the plasma TV display PDP used to realize the present invention.

Detailed ways

Referring to Fig. 1-3, it is the graph used for carrying out the grayscale correction that is referred to in the algorithm of the present invention, as can be seen in the figure, the maximum grayscale value M of the reproduced image is divided into grades, and different grades select different weighting schemes to reproduce the image The smaller the maximum gray value of , the smaller the selected minimum weight. With reference to Fig. 4, realize the block schematic diagram of algorithm of the present invention, as shown in Fig. 4. The schematic diagram is composed of a peak value extraction circuit 1, a judgment circuit 2, a delay circuit 3, an inverse gamma correction circuit 4, an encoder 5, a data processing circuit 6 and a pulse number processing circuit 7, except for the peak value extraction circuit 1, the judgment circuit 2 and Except that the delay circuit 3 is unique to the present invention, all the other circuits are basic circuits of the PDP.

The processing process of the circuit is similar to the three signals of red, green, and blue, that is, R, G, and B. The following only analyzes the processing process of the red, that is, the R signal. The peak extraction circuit is a comparator that compares the R signals of adjacent pixels and outputs a larger R signal. In a TV field, with the continuous transmission of the R signal, the comparison process goes through the full screen pixels, and finally, the peak extraction What the circuit outputs is the maximum R signal of the current image, i.e. the maximum gray value M of the R signal. The judging circuit 2 selects the weight scheme according to Table 2 to control the encoder 5 and the pulse number processing circuit 7 according to the size of M. At the same time, press Table 3 selects the quantization bit width to control the anti-gamma correction circuit 4, the peak value extraction circuit needs a period of time to extract the maximum gray value M in an image, and the delay circuit 3 delays the RGB signal for a period of time, so that it enters the anti-γ The RGB signal of the correction circuit corresponds to the control signal calculated by the judgment circuit according to the field, and the encoder outputs the encoded image data, which is sent to the data processing circuit 6 for processing, the data processing circuit 6, the pulse number processing circuit 7 and the driver circuit 8 The working principles of the circuit and the like belong to the prior art, and will not be repeated here.

In order to improve the reliability of circuit work, the peak value extraction circuit is very important to the detection of the maximum gray value M. Unless it is disturbed, a single isolated pixel with bright light rarely appears on the TV picture, and the bright light-emitting area is generally one or more pixel groups. Based on this fact, M takes the first N maximum gray value of the whole picture Arithmetic mean value, N can be between 50 and 100, the method of comparison and sorting is adopted in the circuit, a field of image signals is compared and sorted, and the first N maximum values are extracted, and the arithmetic mean value is M.

Claims (1)

1. drive controlling method that strengthens low grey degree value picture details, the basic circuit that comprises plasma display panel (PDP), anti-gamma correction method, on the basis of described basic circuit, increase the peak extraction circuit again, decision circuitry and delay circuit, constitute special correcting circuit, it is characterized in that, carrying out dynamic anti-γ proofreaies and correct, under the constant situation of the sub-number of fields order of plasma display panel (PDP), make quantize the bit wide value can be with the adaptive change of the peak brightness of reproduced image, to reduce the gradation loss that reproduces low gray-value image, described decision circuitry, according to the peak extraction circuit, extract the big or small weight selection scheme of the maximum gradation value M in the field picture and remove controlled encoder and umber of pulse treatment circuit, select to quantize bit wide simultaneously and remove to control anti-checking gamma circuit; Described delay circuit with signal delay one field time, makes the signal that enters anti-checking gamma circuit corresponding according to the control signal that this calculates with decision circuitry.

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