The over-driving method of LCD
Technical field
The present invention relates to a kind of driving method of LCD, particularly a kind of over-driving method of LCD.
Background technology
LCD adopts stable state display mode (hold type) usually, because therefore the speed that the liquid crystal molecule response speed changes less than electric field need one period response time just can reach the brightness of target.
The actual response time of liquid crystal is Ton+Toff, it is the time sum that liquid crystal is opened fully and turn-offed fully, usually definition of T on/Toff is that brightness changes 10%~90% time of (perhaps 90%~10%), as shown in Figure 1, thus the response time of liquid crystal reality will much larger than the definition response time.In addition, the situation of the Ton/Toff under this definition (complete in white complete black, perhaps opposite) also is of little use, and usefulness more is the switching between GTG usually.Liquid crystal under the conventional response timing definition has been applied in maximum driving voltage, therefore has the response time faster; And when switching between the GTG, the voltage that is applied is often smaller, therefore has the slower response time, and the response time between GTG generally can be for several frames than long many of Ton/Toff response time.
Response time is the important performance characteristic of LCD, if the response time is long, original image can not disappear at once and the smear phenomenon occurs in the time of can making picture conversion, especially when watching automobile race, action movie or recreation, can have a strong impact on the picture watching quality.Therefore, it is most important to improve response time of liquid crystal.
Reducing the liquid crystal pixel response time mainly contains four methods: reduce liquid crystal material the coefficient of viscosity, improve liquid crystal material dielectric coefficient, reduce the liquid crystal layer gap and improve liquid crystal drive voltage.Wherein the former two is with to improve liquid crystal material character relevant, the latter two then with technology, it is relevant that display drives design.
(overdriving) technology of overdriving is utilizes the raising liquid crystal drive voltage to reduce the technological means of response time, and its principle as shown in Figure 2.The module of overdriving places between Video Controller and the LCD module, and it is the signal G of present frame relatively
nSignal G with former frame
N-1, export a revised data G ' then
nBe used for pixel drive, output G ' overdrives
nProvide by certain algorithm by a table of comparisons that is solidificated in the ROM.Following rule is deferred in concrete comparison and output:
G′
n>G
n if?G
n>G
n-1
G′
n=G
n if?G
n=G
n-1 (1)
G′
n<G
n if?G
n<G
n-1
In Fig. 3, suppose before the n frame GTG signal G
N-1Applied the sufficiently long time, liquid crystal molecule has reached steady state (SS).When the n frame arrived, the GTG signal became G
n, and will keep several frames.The response curve that does not adopt overdrive technique needs the above time of 3 frames could arrive target gray scale as realizing among Fig. 3 shown in a; Dotted line b is the output G ' that overdrives among the figure
nResponse curve.Output G ' overdrives
nMake liquid crystal when the n frame end, reach required GTG G
n, driving voltage is by G ' in the continuous several frames after the n frame
nBecome G again
n, keep the stable of brightness.As seen, overdrive technique makes the time of LCD in a frame arrive target gray scale, has shortened the response time widely.Output G ' overdrives
nBe decided by that initial target gray scale is to (G
n, G
N-1) and Fig. 2 shown in table of comparisons LUT (Look Up Table).
In order to save the space of read only memory ROM, the table of comparisons is generally the two-dimentional sparse matrix of n * n, and therefore, the output of in most cases overdriving can not directly obtain by tabling look-up, and need obtain by interpolation algorithm.Interpolation algorithm commonly used at present has nearest neighbor point interpolation, bilinear interpolation, trigonometric interpolation and bicubic interpolation etc.
The nearest neighbor point interpolation claims the zeroth order interpolation again, and the pixel value of its output equals the nearest input pixel value in position that is mapped to apart from it.For two dimensional image, this method is " getting the gray-scale value of the gray-scale value of 1 adjoint point treating around the sampled point that 4 neighbor pixel middle distances are nearest as this point ".The advantage of nearest neighbor point interpolation is that algorithm is simple, fast operation.But owing to only use the value of the gray-scale value of (being nearest) pixel that this sampled point is had the greatest impact as this point, and do not consider the influence (correlativity) of other neighbors, its shortcoming is that the gradation of image value behind the resampling has tangible uncontinuity, interpolation is of poor quality, can produce artificial vestige in image, image easily produces mosaic and edge sawtooth etc.
Bilinear interpolation claims the single order interpolation again, and it is earlier to carrying out the first-order linear interpolation on the horizontal direction, and then to carrying out the first-order linear interpolation on the vertical direction, rather than on both direction, be linear simultaneously, perhaps conversely, at last both merging are got up.This method is " gray-scale value of 4 adjoint points is done linear interpolation to obtain treating the gray-scale value of sampled point around utilizing on both direction ", promptly according to treating that the distance of sampled point and consecutive point determines that corresponding weights calculate the gray-scale value for the treatment of sampled point.Compare with the nearest neighbor point interpolation, bilinear interpolation owing to considered treats around the sampled point that four direct adjoint points treat the influence of sampled point, has therefore overcome the discontinuous shortcoming of the former gray scale substantially, increases to some extent but its cost is a calculated amount.But further see, because the method is only considered the influence of four direct adjoint point gray-scale values, and reckon without the influence of gray-value variation rate (slope is discontinuous) between each adjoint point, therefore has the character of low-pass filter, make that the high fdrequency component of image incurs loss behind the convergent-divergent, the profile of image becomes fuzzyyer.Compare with original image with the method scaled images, still have the problem that picture quality (details) is degenerated and precision reduces that produces owing to computation model is inconsiderate.
Bicubic interpolation claims the cube convolution interpolation again, it is a kind of complicated more interpolation method, promptly " not only consider the influence of four direct adjoint point gray-scale values, also consider the influence of gray-value variation rate between each adjoint point ", utilized and treated that the gray-scale value of bigger neighborhood interior pixel is made cubic interpolation around the sampled point.This method cubic polynomial.Bicubic interpolation can create the image border more level and smooth than bilinear interpolation, but the calculated amount maximum.
Trigonometric interpolation also is in the enterprising line linearity interpolation of both direction, is that with the difference of bilinear interpolation it has only used three adjacent points around it.Because four direct adjoint points are treated the influence of sampled point around having considered to treat sampled point, so have also overcome the discontinuous defective of gray scale substantially, calculated amount also reduces to some extent than bilinear interpolation algorithm simultaneously.Can be with reference to United States Patent (USP) about trigonometric interpolation: US 2005/0146495A1, there be detailed introduction the inside to its characteristics.
The LCD table of comparisons of overdriving generally all is the sparse matrix that adopts n * n, and expression target gray scale and initial GTG equate on the principal diagonal, have the zero-time response, i.e. still image.On the principal diagonal and near interpolation must accurately, surpass susceptibility to a dynamic image because human eye is very responsive to the out of true of still image.But, adopt bilinear interpolation algorithm process still image keeping static relatively output area to produce noise.And when when principal diagonal carries out interpolation, many interpolation techniques cause the image-region of stable color " boiling " phenomenon to occur, because interpolation technique has been forced a kind of gratuitous interference to pixel value.For example, bilinear interpolation can produce a smooth surface, because interpolation result is the weight summation of 4 sampling spots, 4 sampling spots are all influential to the result.So bilinear interpolation is not to produce a straight line that runs through principal diagonal, but produces a curve, as shown in Figure 4.Equate even this means the initial and target gray scale of pixel, also can produce the effect of overdriving.Trigonometric interpolation doing well on diagonal line, as shown in Figure 5.
In sum, interpolation algorithm commonly used at present respectively has relative merits, and algorithms of different is to the impact effect difference of image, in existing over-driving method, usually all be only to adopt a kind of interpolation algorithm to obtain over-drive value, but single algorithm is difficult to obtain optimum picture quality.
Summary of the invention
Technical matters to be solved by this invention is to provide a kind of and adopts the over-driving method of different interpolation algorithms with the LCD of acquisition better picture quality according to different gray-scale areas.
For achieving the above object, the invention provides a kind of overdriving method of LCD, comprise comparison list and multiple interpolation algorithm, this method comprises the steps:
(a) a plurality of GTGs of definition interval;
(b) be the different interpolation algorithm of the interval appointment of each GTG;
Wherein, described a plurality of GTGs interval defines according to the difference of liquid crystal to the GTG speed, for the slow interval of GTG, adopts the high interpolation algorithm of accuracy; For the fast interval of GTG, adopt the high interpolation algorithm of still image stability.
Liquid crystal GTG in the described GTG interval is close.
The interval that described GTG is slow is corresponding to the mild part of liquid crystal printing opacity curve.
The interval that described GTG is fast is corresponding to the precipitous part of liquid crystal printing opacity curve.
The interpolation algorithm that described accuracy is high can adopt bilinear interpolation algorithm or bicubic interpolation algorithm.
The high interpolation algorithm of described still image stability can adopt the trigonometric interpolation algorithm.
The present invention combines the advantage of existing various algorithms because different algorithms has been selected for use in different GTG intervals, has obtained the optimum picture quality that single algorithm is difficult to acquisition.Especially to the slow mild part in liquid crystal printing opacity curve two ends of GTG, adopt bilinear interpolation algorithm or bicubic interpolation algorithm, guaranteed result's accuracy, obtained precise image; The liquid crystal printing opacity curve precipitous part fast to GTG adopts trigonometric interpolation algorithm or other algorithm, guaranteed that still image is stable.
Description of drawings
Fig. 1 is the printing opacity curve of common liquid crystals display liquid crystal;
Fig. 2 is a LCD overdrive circuit block scheme;
Fig. 3 is the LCD schematic diagram of overdriving;
Fig. 4 A is each the GTG value on the table of comparisons diagonal line of overdriving that adopts the bilinear interpolation algorithm and obtain;
Fig. 4 B is the enlarged drawing in GTG interval among Fig. 4 A;
Fig. 5 A is each the GTG value on the table of comparisons diagonal line of overdriving that adopts the trigonometric interpolation algorithm and obtain;
Fig. 5 B is the enlarged drawing in GTG interval among Fig. 5 A;
Fig. 6 is the process flow diagram of the embodiment of the invention.
Among the figure:
100: enter the computing module 101 of overdriving: define a plurality of GTGs interval
102: accept input data 103: determine between the target gray scale location
104, the different interpolation algorithms of overdriving is selected in different intervals for use
105, over-drive value output
Embodiment
Describe the specific embodiment of the present invention in detail below in conjunction with accompanying drawing.
Fig. 1 is the printing opacity curve of common liquid crystals display liquid crystal.
With reference to Fig. 1, at first define a plurality of GTGs interval: as can be seen from Figure 1 liquid crystal has obvious different to GTG 10% and about 90%, therefore 0~10% part is defined as the first GTG interval, 10%~90% is defined as the second GTG interval, and 90%~100% is defined as the 3rd GTG interval.Because the printing opacity curve of different liquid crystal is inequality, can mark off different GTG intervals fully according to the difference of the light transmission features of liquid crystal.The GTG interval not necessarily is divided into 3, also can be 2,4 and not wait, and sees that specifically GTG has or not significant change.
Fig. 4 is each GTG value and the interval enlarged drawing of GTG thereof on the table of comparisons diagonal line of overdriving that adopts the bilinear interpolation algorithm and obtain; Fig. 5 is each GTG value and the interval enlarged drawing of GTG thereof on the table of comparisons diagonal line of overdriving that adopts the trigonometric interpolation algorithm and obtain.
Then with reference to Fig. 4, Fig. 5, specify the interpolation algorithm of overdriving for each GTG is interval: as can be seen from Figure 4, bilinear interpolation can obtain the smooth curve of pixel gray level transition, therefore is the interval and interval bilinear interpolation algorithm of specifying of the 3rd GTG of first GTG; As can be seen from Figure 5, trigonometric interpolation doing well on diagonal line when the initial and target gray scale of pixel equates, can produce the effect of overdriving hardly, therefore is the interval trigonometric interpolation algorithm of specifying of second GTG.Certainly the present invention is not limited only to this 2 kinds of algorithms, also can be other algorithm, as long as be fit to the interval characteristic of the different GTGs of liquid crystal.
With reference to Fig. 6, describe implementing procedure of the present invention in detail at last:
100 for entering the computing module of overdriving, 101 is a plurality of GTGs of the printing opacity curve definitions interval according to liquid crystal, 102 for accepting the data of input, the data of input comprise initial GTG and target gray scale, initial GTG is former frame GTG signal, target gray scale is present frame GTG signal, 103 is the target gray scale data according to input, judge the GTG interval at target gray scale place, enter step 104 then, be that different GTG intervals utilizes this interval to go up the interpolation algorithm of overdriving of appointment, according to initial GTG, target gray scale, calculate the needed GTG of overdriving with the table of comparisons, step 105 is upgraded former frame GTG signal for calculating the over-drive value that the back acquisition is wanted, and prepares to accept in proper order next frame GTG signal.
The above only describes the present invention in detail with preferred embodiment, and person skilled in the art person can know understanding, and various variations and the change carried out under scope that does not break away from claim of the present invention and spirit do not break away from the spirit and scope of the present invention.