This invention relates to a controller circuit, preferably in the form of a semiconductor integrated circuit (IC), for processing video data for liquid crystal matrix display devices, the circuit having an input to which video data is applied and an output from which processed video data is supplied for the pixels of the display device.
In a typical active matrix liquid crystal display device, (AMLCD), a video signal, for example from a computer or other source, is supplied to video signal processing and control circuitry which outputs processed video signals and timing signals to row (selection) and column (source) driver circuits associated with the pixel array of the display panel and which are responsible for sampling the data of the video signal and applying the samples, in the form of data voltage signals, to the appropriate pixels of the array on a row by row basis. The row and column driver circuits, which usually comprise a shift register circuits with the latter also including a sample and hold circuit, can be provided in the form of ICs mounted on the LC display panel or possibly, if the nature of the technology used in the pixel array permits, as in the case for example of polysilicon TFT devices being used as pixel switches, fully integrated on the panel and fabricated simultaneously with the pixel array using the same thin film electronics technology.
An example of the above-described kind of active matrix liquid crystal display device and its general manner of operation is described in U.S. Pat. No. 5,130,829 to which reference is invited for further information.
Normally the video signal processing and the timing and control circuitry is implemented in the form of one or more silicon integrated circuits (ICs) with the processing being performed digitally.
The signal processing functions performed on the applied video signal by the video signal processing and control circuitry can be various.
The present invention is concerned particularly, although not exclusively, with video signal processing for avoiding or reducing unwanted artefacts in the displayed picture due to behavioural effects of the pixels and also for gamma correction and colour temperature correction.
For gamma, colour and kickback corrections, then Look Up Tables (LUTs) can be used to provide correctional values. For the latter correction, data signal sign information usually also would be required. In AMLCDs, the data voltage signals applied to the pixels have to be periodically inverted to prevent any net DC voltage across the LC material, the inversion being for example for every successive frame (so-called field inversion) or, in addition, for every successive row of pixels (so-called line or row inversion), for adjacent columns of pixels (so-called column inversion) or such that adjacent pixels in both the row and column direction are of opposite polarity (so-called pixel inversion), according to the particular inversion drive scheme employed.
In order to reduce the extent of perceived blurring in the display picture when displaying moving images, which results from the inherent behaviour of the pixels, and particularly the slow response characteristics of the LC material to pixel voltage changes, then preferably the video data processing includes correction for achieving motion blur reduction, a preferred example of such being described in U.S. Pat. No. 5,495,265 (PHN 13505), which requires for this purpose data signal information from one field to the next, and thus a field store for storing at least the data signal values for one field, as well as a LUT.
It is an object of the present invention to provide for use with a matrix display device an improved controller circuit for performing certain video signal processing operations.
It is another object of the present invention to provide a matrix display device controller circuit for performing certain video signal processing functions which can be produced as an IC at lower cost.
According to the present invention, there is provided a controller circuit for processing video data for a colour active matrix liquid crystal display device and having an input for video data processing circuitry for processing the video data and an output from which the processed video data is provided for supply to a driver circuit of the display device, wherein the processing circuitry comprises gamma and colour correction circuits which include a Look-Up Table, and a motion blur reduction circuit for modifying the video data so as to reduce perceived blurring in moving images displayed on the display device and comprising a field store for video data and a Look-Up Table, and wherein the motion blur reduction circuit precedes the gamma and colour correction circuits.
The invention provides a controller circuit for use in the driving of an active matrix LC display device and implementable in IC form which performs certain video signal processing functions to improve the quality of the picture produced by the display device and in which the circuits for performing the video signal processing functions are arranged and organised in the circuit in a manner which makes more efficient use of the semiconductor material whereby the area of semiconductor material required, and hence cost of the IC, is reduced.
The video signal processing functions performed comprise gamma correction, colour correction (to achieve white of a desired colour temperature), and motion blur reduction (to reduce blurring caused by the behaviour of the pixel, particularly the slow response to the LC material to pixel voltage change,) when displaying moving images. Preferably, the controller circuit further includes a kickback correction circuit which also follows the motion blur reduction circuit.
Having regard to the nature of these different corrections, it would be thought in principle appropriate for the gamma and colour corrections, and the kickback correction if present, to be carried out first and the motion blur correction to be carried out last as the former corrections are made to the video data in order to get the correct voltages on the pixels in the static case and the motion blur reduction is then supposed to ensure that those same voltages appear on the pixels despite the temporal response behaviour of the pixel. However, the motion blur reduction processing of the video data signals is, in accordance with the invention, arranged instead to be carried out before the gamma, colour and optional kickback corrections. This leads to less complexity and allows the field store required for the motion blur reduction to be narrower, (fewer bits for each data value) than is the case when motion blur reduction processing is performed last, which arrangement necessitates separate correction of the positive and negative drive ranges. Moreover, the size of the associated LUT will be smaller. Substantial benefits are then obtained when the circuitry is translated into IC form, particularly in terms of the area of silicon required.
The gamma, colour and optional kickback corrections could all be performed using a single, suitably programmed, Look Up Table (LUT).
However, in a preferred embodiment incorporating kickback correction the gamma and colour corrections are performed together, using a single LUT, after the motion blur reduction processing, and the kickback correction is performed lastly. With this arrangement the size of the necessary LUT for gamma and colour correction can be considerably reduced as the need to take into account the sign of the data signal (the data signal voltages applied to the pixels periodically being inverted according to particular drive scheme employed) is required only for the kickback correction (because this is drive polarity dependent) and gamma and colour corrections can be made on the xe2x80x9cunsignedxe2x80x9d data value. Although a LUT is still needed for kickback correction this is smaller than the reduction in size enabled for the LUT associated with the gamma and colour combined so that, overall, the combined sizes of the LUTs is reduced.
This size reduction results in further beneficial reduction in the semiconductor area (i.e. silicon) needed for the IC, and consequently a lower cost IC.