CN100377205C

CN100377205C - Method for compensating gamma value of image signal sampled by using non-linearity

Info

Publication number: CN100377205C
Application number: CNB2003101190452A
Authority: CN
Inventors: 李沈鸿
Original assignee: LG Electronics Nanjing Plasma Co Ltd
Priority date: 2003-12-12
Filing date: 2003-12-12
Publication date: 2008-03-26
Anticipated expiration: 2023-12-12
Also published as: CN1627357A

Abstract

The present invention relates to a nonlinear sampling image signal gray scale coefficient correction method for a display appliance in the process of correcting a gray scale coefficient, which ensures that the gray scale of a low light area and a brightening area reaches the effect of the optimal quality of a picture. The nonlinear sampling image signal gray scale coefficient correction method for a display appliance comprises the following periods: the grey scale of a white signal and the grey scale of a black signal are respectively measured, and grey scale difference is calculated; the grey scale is measured according to an input signal standard input by the bit number of input signals, the measured grey scale and the calculated grey scale difference are used as 100% of reference, and conversion is carried out; the signal standards of the input signals are respectively converted, the grey scale value (Ln) is compared with the set grey scale value, if the two values are not consistent, RGB data values (Yn) need to be increased or decreased, and the RGB data values (Yn) are ensured to be calculated and preserved under the condition of the two values being kept consistent; the deviation values of the RGB data values (Yn) are searched, the non-linear sampling processes of the deviation values are carried out according to the sequence of a larger one to a smaller one, and the sampled deviation values are stored in a storage, etc. The present invention can enhance the quality of the picture of an image and cause the gray scale of the low light area and the brightening area to be perfectly displayed.

Description

Image signal gray coefficient compensation method using non-linear sampling

Technical Field

The invention relates to a gamma correction method for digital display equipment, in particular to a method for adding and writing gamma of image signals by using nonlinear sampling, which can ensure the best nonlinear sampling gamma of the gray of a low light area (low light) and a highlight area (high light).

Background

In recent years, the a/V market has been rapidly expanding, and thus consumers have been increasingly evaluating video image quality, and enthusiasts who can evaluate even fine parts of a screen have been rapidly expanding.

Therefore, the field of gamma correction, which is crucial to image quality, is also attracting attention, and all enterprises are engaged in development of independent technologies. Now, the correction of the gamma in the digital display device is mainly a way of searching a V-T (Voltage transmission) signal curve passing through the display device, searching a curve inscribed with the curve as an area, and then adjusting to an appropriate gamma curve.

Hereinafter, a method of correcting a gamma of a display device according to a conventional art will be described with reference to the accompanying drawings.

Fig. 1 is a V-T graph of a general liquid crystal display device, and fig. 2 is a gamma correction graph of the liquid crystal display device.

Further, fig. 3 is a flowchart of a method for searching a gamma correction curve according to the conventional art, and fig. 4 is a graph of a gamma correction curve searched by the conventional art shown in fig. 3.

FIG. 1 shows a V-T curve of an LCD. As will be seen from a careful examination of FIG. 1, the V-T curve itself is Non-Linear, and particularly, the Liquid Crystal display device (Liquid Crystal display; LCD) itself cannot absolutely display a Low Light (Low Light) portion and a highlight (High Light) portion. If the image signal having the curved pattern shown in fig. 1 is directly passed through without any process, the image of the low light area portion is not recognized, and the highlight portion is too bright.

Therefore, in order to convert such an LCD characteristic curve into a Linear (Linear) gamma curve (or a gamma curve that we need), it should be passed through a gamma correction curve corresponding to the inverse function of the V-T curve.

The gamma correction curve corresponding to the inverse V-T curve is shown in fig. 2.

That is, the gamma correction curve of fig. 2 represents a gamma correction curve converted into a linear gamma curve (or a gamma curve we need) by a signal of the LCD.

The curve of fig. 2 can be roughly divided into 3 parts, such as low bright area, middle bright area, and highlight area, wherein the middle bright area of the gamma correction curve is linear, and the low bright area and the highlight area are protruded curves.

The gamma correction curve with the morphological characteristics has a direct relationship with the characteristics of the LCD itself.

Since the V-T curve middle gray level of the LCD shows a linear characteristic, it is converted into a linear gray level coefficient curve (or a gray level coefficient curve we need) when passing through the linear gray level coefficient correction curve.

However, since the LCD V-T curve in the low light region has almost no luminance change amount with respect to the input signal, data should be forcibly inserted in order to ensure that the gamma curve in the low light region can be converted into a linear curve.

Unlike the above, the output of the LCD V-T curve in the highlight region changes significantly when the input signal changes slightly, and data should be inserted forcibly to convert the gamma curve in the highlight region into a linear curve, so that the brightness does not change significantly when the input signal changes.

Such a gamma correction curve search method of the conventional art is shown in fig. 3, and fig. 3 lists a case where an 8-bit digital signal is input, and ignores white balance correction because it is used to describe a curve for plotting a gray scale.

The conventional method for searching gamma correction curve is to input white signal (255/255W hite) and then measure the gray level. (S301)

The gray scale was measured after the input of the Black signal (0/255 Black) was completed. (S302)

After the measured White-Black signal (White-Black) gradation is set to 100%, the adjustment stage of the gamma correction curve data is performed (S303).

The portion indicated by the broken line in fig. 3 is a stage of adjusting the gamma correction curve data, measures the gray scale of a different stage, and adjusts the gamma correction curve data (Y16 n) until the gray scale reaches a predetermined gray scale (2.2 gamma curve is taken as an example in fig. 3).

First, a 16n/255 signal is inputted, and then the gradation (L16 n) is measured. (n =0,1,2,. 15& 1dn = 255) (S304)

That is, the input signal was measured in 16 gradations from Black to white, and L16n is a value obtained by converting (W hite-Black) to 100%.

In addition, the measured gray value (L16 n) is compared with a preset gray value to see whether the gray values are consistent. (S305)

Here, the preset gradation value is exemplified by an 8-bit data signal and a 2.2 gamma curve, and the specific calculation method is as follows:

with mathematical formula 1:

and (6) performing calculation.

If the comparison result indicates that the measured gradation value does not coincide with the previously set gradation value, it is determined which of the two values is larger (S307), and if the previously set gradation value is certainly larger, the RGB data value should be increased (Y16 n). (S308)

If the previously set gray scale value is not large but the measured gray scale value is large, the RGB data value (Y16 n) should be decreased (S309). (S310)

In the previous step S305, if the comparison result shows that the preset gradation value matches the measured gradation value, the RGB data value Y (L16 n) under the corresponding condition is obtained, and it is determined whether or not (S3 06) n =16, and n is gradually increased by adding "1" until n = 16. The gamma correction curve data (Y16 n) adjustment stage is repeatedly performed. (S312)

At this stage, a relative gradation value Y255= Y (L255) of the 8-bit digital data is obtained, and a value Y16n is recorded in the memory (S313). (S314)

Subsequently, correction (interpolation) is performed for values other than Y16 n.

If the gamma correction curve is searched by a conventional technique, a gamma correction curve as shown in fig. 4 will be obtained.

A careful examination of fig. 4 reveals that neither the low light portion nor the highlight portion is fully displayed.

This is because the input video signal is received at regular intervals and corrected by obtaining the gamma value, and the values therebetween are obtained by linear correction.

Since the gamma correction method of the conventional display device is linear in the LCD characteristic of the middle gray, even if the correction method is used, the actually searched gamma correction curve has a large difference from the ideal gamma correction curve, and for the low-light gray and the highlight gray, the LCD characteristic is represented in a curved form, and if the correction is performed, the difference from the ideal gamma correction curve is large.

Disclosure of Invention

The present invention has been developed in order to solve the problems of the conventional art described above. The invention aims to provide a method for correcting the gray scale coefficient of an image signal by utilizing nonlinear sampling, which adopts a nonlinear sampling mode to ensure that the image quality of the gray scales of a low light area and a highlight area achieves the best effect.

The object of the present invention is achieved by a method for correcting a gamma of a sampled video signal, which comprises the following steps: the stage of measuring the gray scale of white signal and the gray scale of black signal separately and calculating the gray scale difference; gray scale measurement of signal standard input according to different input signal bit numberA step of converting the measured gray scale according to the obtained gray scale difference by a standard of 100%; comparing the gray scale value converted respectively to the signal standard of the input signal with the set gray scale value, if the two values are not consistent, the RGB data value should be increased or decreased, and the RGB data value is calculated and stored under the condition that the two values are consistent; searching deviation values of RGB data values, carrying out nonlinear sampling on the deviation values according to the size sequence, and storing the deviation values in a memory at a medium stage; the preset gray scale value is a gray scale value calculated from an ideal gamma curve, and is determined by the following formula:

wherein n =0,1,2 \8230; 255.

The invention has the following effects: the invention adopts the image signal gray coefficient correction method of nonlinear sampling to correct the gray coefficient of nonlinear digital display equipment such as LCD, etc., can use the ideal gray coefficient correction curve, for the gray coefficient correction mode of the input signal with larger variation, can get the gray coefficient correction curve closest to the ideal gray coefficient correction curve.

The display device can completely display the low light area part and the bright area part, and greatly improves the image effect.

Drawings

Fig. 1 is a V-T curve diagram of a general liquid crystal display device.

Fig. 2 is a gamma correction curve chart of the liquid crystal display device.

Fig. 3 is a flowchart of a gamma correction method of the search conventional art.

Fig. 4 is a graph showing gamma correction for searching in the conventional art shown in fig. 3.

Fig. 5 is a flow chart of a method of searching gamma correction curves according to the method of the present invention.

Fig. 6 is a graph of gamma correction searched by the method of the present invention shown in fig. 5.

Fig. 7 is a search bias sample list of gamma correction curves of the present invention.

The invention will be further described in detail by way of examples with reference to the accompanying drawings, but the following examples are only illustrative of the invention and do not represent the scope of the invention as defined in the claims.

Detailed Description

Example 1

Fig. 5 is a flowchart illustrating a gamma correction curve search method according to the present invention, fig. 6 is a graph illustrating a gamma correction curve searched for according to the present invention shown in fig. 5, and fig. 7 is a sampling table for searching for a bias of a gamma correction curve according to the present invention.

The present invention is a method for ensuring optimization of low-light area gray scale and highlight area gray scale in a display device using a Non-Linear (Non-Linear) curve as a V-T curve, as one of the video signal gamma correction methods.

Especially, the error range caused by the linear correction method is minimized, and the image quality under the gray scale of the low light area and the gray scale of the highlight area can be greatly improved.

The gamma correction method using the non-linear sampling image signal of the present invention has the following 3 features:

first, in reading the luminance of an input signal, a standard interval of the input signal is input non-linearly.

Then, in order to ensure that the standard interval of the input signal is input in a nonlinear manner, the deviation value of the ideal gamma correction curve is used to accurately adjust the portion having a large deviation value.

Thirdly, after the part with larger deviation value is precisely adjusted, the process of correcting the residual value is also included.

As described above, the present invention is not a method of measuring output luminance to obtain a gamma correction curve while quantitatively increasing the input image signal standard, but a method of obtaining an ideal gamma correction curve, and performing gamma correction on an input signal having a large variation amount of variation by using the deviation of the ideal gamma correction curve.

Since the V-T (Voltage-transmission) curve of the LCD is non-linear, if the input Voltage (Voltage) is converted into a non-linear input, its characteristic can be converted into linear.

In order to input a voltage that ensures that the output luminance has linear characteristics, it is necessary to obtain an ideal gamma correction curve.

The ideal gamma correction curve is an R, G, B data value that is forcibly recognized in order to ensure that input is performed at a level at which input voltage can be displayed, and that possible input luminance is read to form a linear gamma curve (or a desired gamma curve).

In the embodiment of the present invention, the desired gamma curve is assumed to be a 2.2 gamma curve, and the input voltage standard is assumed to be 8 bits.

Fig. 6 shows an ideal gamma correction curve searched under such conditions and a gamma correction curve using the nonlinear sampling method in the present invention.

The gamma correction method of the present invention is explained in detail as follows:

fig. 5 is an example of an 8-bit digital input signal, and since the gradation curve is drawn, the white balance correction can be omitted.

Since the input voltage is assumed to be normalized to 8 bits, the input voltage is normalized from 0 to 255.

First, a White signal (255/255 White) is inputted, and then the gradation is measured. (S501)

Next, the gray scale was measured after inputting the Black signal (0/255 Black). (S502)

And adjusting the gray coefficient correction curve data after setting the gray of the White signal-Black signal (White-Black) as 100% (S5 03).

The portion indicated by the dotted line in fig. 5 indicates the stage of adjusting the gamma correction curve data to measure the gray scale of the input signal (from black to white; n/255). (initially n =0,1, 2.., 255) (S504)

The measured gray values are then compared with the previously set gray values to see if they match. (S505)

Here, the preset gradation value is exemplified by an 8-bit data signal and a 2.2 gamma curve, and therefore, the calculation can be performed as follows.

With mathematical formula 2:

to calculate.

If the measured gray-level value does not match the result of the comparison with the preset gray-level value, it is determined which of the two values is greater (S508), and if the preset gray-level value is greater, the RG B data value should be increased. (S509)

If the previously set gray scale value is not large, it is judged that the measured gray scale value is large, and the RGB data value should be decreased (S510). (S511)

If the comparison result in the above-described step S505 shows that the preset gradation value matches the measured gradation value, the RGB data value under the corresponding condition is obtained (S506), and the obtained value is temporarily recorded in the memory. (S507)

Whether n =255 is judged, and the value of n is gradually increased by adding "1" until n = 255. The gamma correction curve data (Y16 n) adjustment step is repeatedly performed. (S513)

Here, when the value of n is not 255, the repetition of the corresponding phase may be stopped when the corresponding phase operation is performed again in different phases than when the RGB data value is adjusted.

After the adjustment process of the data RGB data values is performed, the deviation values of the data RGB data values are found out. (S514)

This method of searching for a data RGB data value deviation value has the same effect as the 2-time differential gamma correction curve method.

Further, the data RGB data values having a large offset value are recorded in the memory by 16-step sampling (S515) by taking an example of the order of the magnitude of the offset value of the data RGB data values. (S516)

Assuming that such an input signal is 8 bits, when the correction is performed by the nonlinear sampling method in the present invention, as shown in fig. 6, a gamma correction curve obtained by performing the correction after inputting a nonlinear voltage is almost the same as an ideal gamma correction curve.

Especially, in the low light area gray scale and the highlight area gray scale, the gray scale characteristic can be fully displayed.

Fig. 7 illustrates a method of searching for a bias value, which requires a long time to search for an ideal gamma correction curve for all LCD panels, and thus searches for a gamma correction curve in the following manner.

First, an ideal gamma correction curve is sequentially obtained from n =0, and when the deviation reaches a specific Threshold value (Threshold), that is, an input level at which the deviation value of the ideal gamma correction curve hardly changes, the adjustment is stopped, and after the value is recorded, the ideal gamma correction curve is reversely obtained from n = 255.

And stopping the adjustment if the ideal gamma correction curve deviation value reaches a specific limit value, and performing gamma correction curve search for an input standard opposite to the input standard already found.

In the table of fig. 7, (Y') is a deviation of the gamma correction curve, that is, a deviation value between any two points, and (Y "n) is a deviation value of the gamma correction curve, that is, a variation amount of the deviation value.

The sampling is performed sequentially from the larger value of (Y' n).

If this method is used, a lot of time can be saved because it is not necessary to read all 256 input standards.

Since it represents the linear characteristic of the V-T curve of the middle-bright-area gray-scale LCD, when the gamma correction curve is searched using the above method, a large error does not occur compared with the entire gamma correction curve.

The other method is to find the gamma correction curves of several LCD panels and find the adjusted input standard average value, which is suitable for other LCD methods.

The LCD has a V-T curve which is relatively close according to different manufacturers and panel sizes, so that the method can be used.

Claims

1. A gamma correction method for image signals using non-linear sampling is characterized by comprising the following stages:

the stage of measuring the gray scale of white signal and the gray scale of black signal separately to obtain the gray scale difference;

a stage of respectively measuring gray scales of signal standards inputted according to input signal bits and converting the measured gray scales and the obtained gray scale difference according to a 100% standard;

comparing the gray scale value converted from the signal standard of the input signal with the preset gray scale value to see if they are consistent, if they are not consistent, the RGB data value should be increased or decreased to ensure that the RGB data value is calculated and stored under the condition that two values are consistent;

searching the deviation value of the RGB data value, and carrying out non-linear sampling and recording in a memory according to the sequence of the deviation value from large to small;

the previously set gray-scale value is a gray-scale value calculated from an ideal gamma curve, and the previously set gray-scale value is determined by the following formula:

wherein n =0,1,2 \8230; \8230255.

2. The method for gamma correction of an image signal as set forth in claim 1, wherein: the deviation value searching stage of the RGB data values is a stage of sequentially calculating the gamma correction curves from the lowest input signal standard, stopping adjustment after the deviation value of the gamma correction curves almost reaches a constant limit value, and recording the value.

3. The method for gamma correction of an image signal as set forth in claim 1, wherein: the deviation searching stage of the data RGB data value is a stage of sequentially obtaining a gray coefficient correction curve from the highest input signal standard, stopping adjustment after the deviation value reaches a specific limit value, and recording the value.

4. The method for gamma correction of an image signal as set forth in claim 1, wherein: the step of sampling the deviation values in a non-linear manner in descending order is a step of sampling all the RGB data values in descending order of the deviation values, or sampling some of the RGB data values in descending order of the deviation values.