Liquid crystal display control circuit for reducing memory size by detecting image edges and saving edge data and method thereof

A liquid crystal display (LCD) control circuit is disclosed. The control circuit includes an edge detecting circuit for detecting image edges in each frame of an image data, and outputting an edge data and a non-edge data; a memory for saving the edge data of the frame; a driving decision circuit for generating a driving voltage setting according to the non-edge data of a current frame, and generating an overdriving voltage setting according to the edge data of a previous frame saved in the memory and the edge data of the current frame outputted by the edge detecting circuit; and an output device for outputting the driving voltage setting and the overdriving voltage setting.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display (LCD) control circuit and a control method thereof, and more specifically, to a control circuit and a method thereof that detects image edges of frames to reduce memory size by decreasing saved pixel data when executing the overdriving procedures.

2. Description of the Prior Art

Liquid crystal display (LCD) panels are mass-produced products applied to the field of computers, monitors, and TVs. The operation principle of an LCD is to vary voltages dropped on two terminals of liquid crystal cells in order to change a twisted angle of the liquid crystal cells. The transparency of the liquid crystal cells is changed for achieving the desired objective of illustrating images. Therefore, accurately and appropriately controlling the voltages between two terminals of liquid crystal cells is a key point for showing images rapidly and clearly.

It is well known by those skilled in the art that overdriving procedures are usually executed to reduce response time of the liquid crystal cells as images vary rapidly. Please refer toFIG. 1.FIG. 1is a block diagram of an LCD control circuit100according to the prior art. The control circuit100receives a gray level value of every pixel and determines the voltage applied on the two terminals of the liquid crystal cell corresponding to a pixel unit in accordance with the gray level value difference of the pixel unit between a current frame and a previous frame. AsFIG. 1shows, the control circuit100includes a buffer circuit110, a frame memory120, and a driving-decision circuit130. Gray level values Dinof pixels are inputted into the control circuit100and then delivered to the driving decision circuit130and the frame memory120respectively through the buffer circuit110. The symbol Gnin the figure shows the data is the gray level value of pixels in the current frame. The frame memory120records inputted gray level values and outputs a pre-saved gray level value Gn-1that corresponds to the pixels in the previous frame to the driving decision circuit130. Next, the driving decision circuit130compares the gray level value Gnof the current frame and the gray level value Gn-1of the previous frame and then compares the difference between these two gray level values with the value saved in a look-up table to determine whether the control circuit100has to execute overdriving procedures and therefore whether a corresponding voltage will be dropped on the liquid crystal cells when the overdriving procedure is executed. Finally, the driving-decision circuit130outputs a driving voltage setting Soutto a voltage supply circuit to provide the voltage dropped on two terminals of the liquid crystal layer.

Because the frame memory120has to save gray level values of all pixels in a frame, the memory size needs to be large enough to include the gray level values of all pixels in a frame. However, the larger the memory size is, the more expensive it becomes.

SUMMARY OF THE INVENTION

It is therefore one of the objectives of the claimed invention to provide a liquid crystal display (LCD) control circuit and a control method, to solve the above-mentioned problems.

According to an embodiment of the present invention, an LCD control circuit is disclosed. The control circuit includes an edge-detecting circuit for detecting image edges in each frame of an image data, and outputting an edge data and a non-edge data corresponding to each frame; a memory coupled to the edge-detecting circuit, for saving the edge data of the frame; a driving decision circuit coupled to the edge-detecting circuit and the memory, for generating a driving voltage setting according to the non-edge data of a current frame outputted by the edge-detecting circuit, and generating an overdriving voltage setting according to the edge data of a previous frame saved in the memory and the edge data of the current frame outputted by the edge detecting circuit; and an output device coupled to the driving decision circuit, for outputting the driving voltage setting and the overdriving voltage setting.

According to another embodiment of the present invention, an LCD control method is disclosed. The method includes: detecting image edges in each frame of an image data, and outputting an edge data and a non-edge data corresponding to each frame; saving the edge data of the frame; generating a driving voltage setting according to the non-edge data of a current frame and generating an overdriving voltage setting according to the edge data of a previous frame and the edge data of the current frame; and outputting the driving voltage setting and the overdriving voltage setting.

DETAILED DESCRIPTION

Please refer toFIG. 2.FIG. 2is a block diagram of the LCD control circuit200according to a preferred embodiment of the present invention. The control circuit200includes an edge-detecting circuit210, a frame memory220, a driving decision circuit230, and a multiplexer280, wherein the driving decision circuit230consists of a non-edge-driving decision circuit240, an edge-driving decision circuit250, a storage unit260, and a weighted circuit270. The operation principle of the control circuit200is described in the following.

Initially, the gray level values Dinof every pixel in the frame are inputted into the edge-detecting circuit210, and the edge-detecting circuit210detects edge parts of images in the current frame, then classifies the pixel data of the current frame into edge data and non-edge data. The pixel data of edge parts is classified as the edge data and the pixel data of the other parts is classified as the non-edge data. There are many methods, known by those skilled in the art, for detecting the edge parts of images. For example, by comparing gray level values of a pixel and other neighboring pixels in the same frame, it can be determined that the pixel and other neighboring pixels respectively belong to different objects if the gray level values of these pixels are very different. Therefore, the pixel is classified into the edge part. The edge-detecting circuit210outputs the non-edge data Gn,nof the current frame to the non-edge-driving decision circuit240positioned in the driving decision circuit230, and outputs the edge data Gn,eof the current frame to the frame memory220and the edge-driving decision circuit250.

As frames are continuous, if the object is moving, only pixel data (such as light intensity, color etc.) in the edge part of the image has great variation; in other words, only the liquid crystal layer of these pixels in the edge part has to execute an overdriving voltage setting, whereas the liquid crystal layer of other pixels in the other parts of the frame merely needs to execute a general driving voltage setting. Therefore, the non-edge-driving decision circuit240generates the driving voltage setting Sncorresponding to the non-edge part of the current frame according to the non-edge data Gn,n(such as the gray level value of the pixel) of the current frame.

The frame memory220saves the edge data Gn,e(such as the gray level value of the pixel) of the current frame outputted from the edge-detecting circuit210, and then outputs pre-saved edge data Gn-1,eof the previous frame to the edge-driving decision circuit250. The edge-driving decision circuit250compares two edge data Gn,e, Gn-1,ethat respectively correspond to the current frame and the previous frame, and accesses a look-up table stored in the storage unit260in accordance with the difference between these two edge data in order to determine the voltage setting of the liquid crystal layer. For example, if the difference between the edge data Gn,eof the current frame and the edge data Gn-1,ethe previous frame is greater than a threshold value, it means that the edge data varies greatly in these two continuous frames. Hence the look-up table must be accessed to obtain a suitable overdriving voltage setting Secorresponding to the difference for accelerating the response time of the liquid crystal cells. Please note that because the frame memory220only has to save edge data rather than the data of all pixels of the frame, the necessary memory size of the present invention is smaller than the memory size required in the prior art.

In a preferred embodiment of the present invention, for avoiding error and increasing stability of the control circuit200, the driving voltage setting Sncorresponding to the non-edge part of the current frame and the overdriving voltage setting Secorresponding to the edge part of the current frame are inputted into a weighted circuit270. The weighted circuit270references the driving voltage setting Snof the pixels located at the non-edge part neighboring the image edge part for adjusting an initial overdriving voltage setting Seof the edge part, and the weighted circuit270then generates a modified overdriving voltage setting SMcorresponding to the edge part of the current frame. There are many methods for the weighted circuit270to execute the weighted operation. For example, please refer toFIG. 3.FIG. 3is a block diagram of the weighted circuit270shown inFIG. 2according to a preferred embodiment of the present invention. The weighted circuit270includes a first multiplier271, a second multiplier272, and an adder273. The first multiplier271firstly multiplies the driving voltage setting Snof at least one pixel located at the non-edge part next to the edge part in the current frame with a first weighted factor α to generate a first operating value αSn, wherein the first weighted factor α is a value less than1. Next, the second multiplier272multiplies the initial overdriving voltage setting Seof a specific pixel located at the edge part in the current frame with a second weighted factor β to generate a second operating value βSe. Finally, the adder273sums up the first operating value αSnwith the second operating value βSeto generate the modified overdriving voltage setting SMof the specific pixel.

The driving voltage setting Snand the modified overdriving voltage setting SMare inputted into a multiplexer280. The multiplexer280is an output device for outputting the driving voltage setting Snand the modified overdriving voltage setting SM. As mentioned above, the non-edge part of the current frame can directly use the driving voltage setting Snto set a voltage supply circuit (not illustrated in the diagram) to provide the voltage dropped on two terminals of the liquid crystal layer, but the edge part has to use the modified overdriving voltage setting SMto set a voltage supply circuit to provide the voltage dropped on two terminals of the liquid crystal layer. Consequently, the multiplexer280selectively switches the driving voltage setting Snor the modified overdriving voltage setting SMto be the setting value of the voltage supply circuit according to whether the pixel belongs to the edge part or the non-edge part of the frame.

Please refer toFIG. 4.FIG. 4is a flowchart of an LCD control method according to a preferred embodiment of the present invention. Steps of the control method are described below:

Step415: Detect edge parts of each frame, then go to step420and step445sequentially;

Step420: Output an edge data corresponding to each frame, then go to step425and step430sequentially;

Step425: Save the edge data of each frame;

Step430: Access a look-up table according to a previous frame and a current frame;

Step435: Determine an overdriving voltage setting corresponding to the edge part of the current frame in accordance with the look-up table;

Step440: Execute a weighted operation to generate a modified overdriving voltage setting according to the driving voltage setting of the non-edge part and the overdriving voltage setting of the edge part, then go to step455;

Step445: Output a non-edge data corresponding to each frame;

Step450: Generate the driving voltage setting of the non-edge part in the current frame according to the non-edge data, then go to step440and step455sequentially;

Step455: Output the overdriving voltage setting and the driving voltage setting to set the voltage value;