Patent Grant
7929602
This application claims the benefit of Korean Patent Application No. 10-2004-0091850, filed on Nov. 11, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to Dynamic Capacitance Compensation (DCC) for a Liquid Crystal Display (LCD), and more particularly, to an apparatus and method for performing Dynamic Capacitance Compensation (DCC) of a Liquid Crystal Display (LCD), capable of minimizing a chip size and reducing picture-quality deterioration.
2. Description of the Related Art
A Liquid Crystal Display (LCD) displays characters or images using optical variations caused by injecting and arranging liquid crystals between two glass plates and then applying a voltage to change the arrangement of the liquid crystal particles. Since the LCD uses a low voltage of 1.5 through 2 V, it has been widely employed in clocks, calculators, notebook computers, etc.
However, in the LCD, a current image overlaps a previous image due to a slow response speed, which produces blurring. In general, one frame has a duration of about 16.7 ms. When a voltage is applied to both ends of a liquid crystal material, the liquid crystal material responds to the voltage after a predetermined time has elapsed. Accordingly, in order to obtain a desired pixel value, a time delay is needed and such a time delay causes blurring.
In order to improve a response speed of the LCD, Dynamic Capacitance Compensation (DCC) is used. According to the DCC, a difference between a pixel value of a previous frame for an arbitrary pixel and a pixel value of a current frame for the pixel is obtained, and a sum of a value proportional to the difference and the pixel value of the current frame is output. In order to perform the DCC, the pixel values of previous frames must be stored in advance in a memory.
However, to store the pixel values of the previous frames without compression and stably perform the DCC, a write memory for storing the previous pixel values and a read memory for reading the stored pixel values and comparing the stored pixel values with current pixel values are required.
In order to reduce memory loads, a technique of compressing image data can be considered. That is, by compressing pixel values of a previous frame to bit streams using an encoder, storing the compressed bit streams in a memory, decoding the bit streams using a decoder, and comparing the decoded bit streams with pixel values of a current frame, DCC can be performed. Conventionally, color sampling compression has been used to compress pixel values of a previous frame. In the color sampling compression, pixel values of a previous frame are compressed by YCbCr sampling and down-sampling. Here, Y represents Luminance and Cb and Cr represent Chrominance.
However, such color sampling compression causes color changes when data is compressed and has low compression efficiency.
For these reasons, conventionally, to perform DCC in an LCD, a method of storing pixel values of image data for a previous frame without compression or a method of compressing pixel values of image data by color sampling compression with picture-quality deterioration has been used.
Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention.
The present invention provides an apparatus and method for performing Dynamic Capacitance Compensation (DCC) of a Liquid Crystal Display (LCD), capable of minimizing a chip size and reducing picture-quality deterioration.
According to an aspect of the present invention, there is provided an apparatus for performing dynamic capacitance compensation (DCC) in a liquid crystal display (LCD), the apparatus including: a first line buffer reading and temporarily storing pixel values of an image for each line; an encoder transforming and quantizing the pixel values stored for each line for each block and generating bit streams; a memory storing the generated bit streams; a decoder decoding the bit streams stored in the memory for the each block and outputting the decoded bit streams; a second line buffer reading and temporarily storing the decoded pixel values for the each block; and a compensation pixel value detector detecting a compensation pixel value for each pixel, from pixel value differences between pixel values of a current frame stored in the first line buffer and pixel values of a previous frame stored in the second line buffer.
According to another aspect of the present invention, there is provided a method of performing dynamic capacitance compensation (DCC) in a liquid crystal display (LCD), the method including: (a) reading and temporarily storing pixel values of an image for each line; (b) transforming and quantizing the pixel values stored for the each line for each block and generating bit streams; (c) storing the generated bit streams; (d) decoding the stored bit streams for the each block; (e) reading and temporarily storing the decoded pixel values for the each block; and (f) detecting a compensation pixel value for each pixel from pixel value differences between pixel values of a current frame stored in operation (a) and pixel values of a previous frame stored in operation (e).
These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures.
Hereinafter, a Liquid Crystal Display (LCD) according to the present invention will be described with respect to the appended drawings.
The first line buffer 100 reads and temporarily stores pixel values of an image for each line. In detail, the first line buffer 100 reads pixel values of an image of a current frame Fn for each line, temporarily stores the read pixel values for a predetermined number of lines, and outputs them to the decoder 102. If a unit block in which pixel values are encoded by the encoder 102 is a M×M block, the predetermined number of lines is M−1. For example, if a block is a 4×4 block, the first line buffer 100 reads and temporarily stores pixel values corresponding to three lines. When the first line buffer 100 reads pixel values corresponding to a fourth line, the first line buffer 100 outputs the pixel values corresponding to these four lines to the encoder 102.
The encoder 102 transforms and quantizes pixel values of each line for each block and generates bit streams. If the encoder 102 receives pixel values of an image corresponding to each block from the first line buffer 100, the encoder 102 transforms and quantizes the pixel values for each block, generates bit streams, and outputs the generated bit streams to the memory 104.
The spatial image predictor 200 spatially predicts pixel values of a current block using blocks spatially adjacent to the current block and outputs the predicted pixel values to the RGB signal encoder 202. A process of removing spatial redundancy of a block using blocks spatially adjacent to the block is called intra prediction. That is, the spatially predicted pixel values are obtained by estimating prediction directions from a current block and blocks spatially adjacent to the current block for each color component. The spatial image predictor 200 performs intra prediction by removing spatial redundancy between a current block and its peripheral blocks, using spatially predicted and compensated results received from the first spatial image prediction compensator 210, that is, using restored blocks of a current image.
The RGB signal encoder 202 removes redundant information among R, G, and B pixel values of the current block, according to the spatially predicted results of the current block, encodes a resultant RGB signal from which the redundant information is removed, and outputs the encoded RGB signal to the transform and quantization unit 204. In detail, the RGB signal encoder 202 removes redundant R, G, and B pixel values using correlation of spatially predicted pixel values for R, G, and B components, and encodes a RGB signal from which the redundant components are removed.
The transform and quantization unit 204 transforms and quantizes the pixel values in the block and outputs the transformed and quantized pixel values to the first inverse-quantization and inverse-transform unit 206 and the mode decision unit 212. For example, the transform and quantization unit 204 divides and transforms a time-based image signal into frequency-based image signals using Discrete Cosine Transform (DCT). That is, the transform and quantization unit 204 divides and transforms a time-based image signal into high-frequency parts requiring high signal power and low-frequency parts requiring low signal power. After the DCT is performed, the high-frequency parts requiring high signal power are distributed in the upper and left region of the transformed and quantized block and the low-frequency parts requiring low signal power are distributed in the lower and right region of the transformed and quantized block. The block transformed and quantized by the transform and quantization unit 204 is referred to as a transform block.
The first inverse-quantization and inverse-transform unit 206 receives the transform block from the transform and quantization unit 204, performs inverse-quantization and inverse-transform on the transformed and quantized coefficients of the transform block, and outputs the inverse-quantizated and inverse-transformed coefficients to the first RGB signal decoder 208.
The first RGB signal decoder 208 receives the inverse-quantized and inverse-transformed coefficients from the first inverse-quantization and inverse-transform unit 206, decodes a RGB signal of the transform block, and outputs the decoded RGB signal to the first spatial image prediction compensator 210.
The first spatial image prediction compensator 210 receives the decoded RGB signal from the first RGB signal decoder 208, compensates for the spatially predicted pixel values of the transform block, and outputs the compensated pixel values to the spatial image predictor 200.
The mode decision unit 212 sets a division mode for dividing the transform block into a first area in which at least one coefficient is not “0” and a second area in which all coefficients are “0”, along a predetermined diagonal line, and outputs the division mode to the bit depth decision controller 214.
Diagonal lines for setting first through fourth division modes for a 4×4 transform block are not limited to those shown in
In
In
In
In
In
Meanwhile, an embodiment in which a transform block is divided into eight division modes, as shown in
For example, the mode decision unit 212 decides a division mode in which all coefficients of a second area are “0”, among the first through fourth division modes of
The bit depth decision controller 214 decides a second bit depth representing the number of bits required for binarizing each coefficient in the first area, according to whether or not all the coefficients of the first area are within a predetermined value range, in response to a division mode decided by the mode decision unit 112, and outputs the decided second bit depth to the compression rate adjustment request sensor 216. The bit depth means the number of bits used to store information for each pixel in computer graphics. The predetermined value ranges are defined in advance.
Table 1 is a look-up table showing second bit depths corresponding to predetermined value ranges.
If it is assumed that division mode identification information shown in Table 1 represents identification information of the second through fourth division modes for the 4×4 transform block shown in
The bit depth decision controller 214 stores information, such as the look-up table shown in Table 1, in a predetermined memory, to decide a second bit depth.
The coefficient range determination unit 300 determines whether all coefficients of a first area are within a predetermined value range, and outputs the determined result to the flag information setting unit 302. For example, if it is assumed that a predetermined value range, as shown in Table 1, is “−2 through 1” and a division mode decided by the mode decision unit 212 is a second division mode (here, identification information of the second division mode is “1’), the coefficient range determination unit 300 determines whether all coefficients of a first area of the second division mode are within a predetermined value range “−2 through 1”.
If all the coefficients of the first area are between −2 and 1, the flag information setting unit 302 sets first flag information indicating that all the coefficients of the first area are within the predetermined value range “−2 through 1”, in response to the determination result of the coefficient range determination unit 300, and outputs the first flag information to the bit depth decision unit 304.
Meanwhile, the flag information setting unit 302 sets second flag information indicating that at least one of coefficients of a first area is not within a predetermined value range, and outputs the second flag information to the compression rate adjustment request sensor 216 through an output terminal OUT1. For example, it is assumed that the predetermined value range, as shown in Table 1, corresponds to a range “−4 through 3”, and a division mode decided by the mode decision unit 212 is a third division mode (here, identification information of the third division mode is “2”). Referring to
The bit depth decision unit 304 decides a second bit depth, in response to first flag information set by the flag information setting unit 302, and outputs the decided second bit depth to the compression rate adjustment request sensor 216.
The bit depth decision unit 304 decides the second bit depth according to a division mode and a predetermined value range. For example, if first flag information is set, the bit depth decision unit 304, as shown in Table 1, decides a second bit depth “2”, which satisfies a second division mode and corresponds to division mode identification information “1” and a predetermined value range “−2 through 1”. That is, the bit depth decision unit 304 decides a second bit depth to generate a bit stream corresponding to 2 bits for each coefficient of the first area.
Also, the bit depth decision unit 304 can decide the second bit depth to a specific bit depth regardless of the type of a division mode.
The compression rate adjustment request sensor 216 senses whether adjustment of a compression rate of a transform block is requested, in response to a control signal received from the bit depth decision controller 214. If adjustment of the compression rate of the transform block is requested, the compression rate adjustment request sensor 216 outputs the sensed result to the bit depth resetting unit 218. If adjustment of a compression rate of the transform block is not requested, the compression rate adjustment request sensor 216 outputs the sensed result to the bit stream generator 220.
The bit depth resetting unit 218 resets a first bit depth indicating the number of binarized unit bits for each coefficient of the transform block, in response to the sensed result received from the compression rate adjustment request sensor 216, and outputs the reset first bit depth to the transform and quantization unit 204. The transform and quantization unit 204 transforms and quantizes pixel values for the transform block in correspondence to the reset first bit depth.
The first bit depth means the number of bits used to binarize each coefficient of the transform block. Then, the first bit depth is reset using a quantization adjustment value for adjusting a quantization period. Table 2 shows first bit depths corresponding to quantization adjustment values.
As shown in Table 2, as a quantization adjustment value increases, a first bit depth value relatively decreases. The first bit depth value means the number of bits used to binarize each coefficient of a transform block. Since, if a first bit depth value is small, this means that the number of bits used to represent a coefficient is small, a small bit depth value means that a compression rate is high. Accordingly, to increase a compression rate, it is needed to increase a quantization adjustment value and thus decrease a first bit depth value. However, picture quality is deteriorated due to the increase of a compression rate. On the contrary, to decrease a compression rate, it is needed to decrease a quantization adjustment value and thus increase a first bit depth value.
The bit stream generator 120 generates a bit stream for the coefficients of the first area, according to the decided division mode and second bit depth. For example, if it is assumed that a predetermined value range, as shown in Table 1, corresponds to “−2 through 1” and a division mode decided by the mode decision unit 212 is a second division mode, a second bit depth, as shown in Table 1, is decided to 2 [bits]. Referring to
If all coefficients of a transform block are “0”, the bit stream generator 120 generates a bit stream for only identification information of a division mode. For example, as shown in
Also, if the total number of bits used when bit streams of all coefficients of a first area are generated is equal to or greater than the total number of bits used when bit streams of pixel values of a transform block are generated, the bit stream generator 130 generates bit streams of the pixel values of the transform block. For example, if a 4×4 block not subjected to transform and quantization has pixel values each with 8 bits of a bit depth and bit streams are generated using the pixel values of the 4×4 block without compression, 128 bits (16×8=128) are required. If the total number of bits required is greater than or equal to 128 [bits], the bit stream generator 120 generates bit streams of the pixel values of the block not subjected to transform and quantization, without generating bit streams of the transformed and quantized coefficients.
Meanwhile, the bit stream generator 120 generates bit streams of the coefficients of the first area, according to the decided division mode and the predetermined first bit depth. For example, it is assumed that a predetermined value range, as shown in Table 1, is “−4 through 3” and a division mode decided by the mode decision unit 212 is a third mode.
The memory 104 stores bit streams generated by the encoder 102. In the present invention, since pixel values for previous frames are compressed and stored, a high capacity memory is not required. Accordingly, in the present invention, all of a write memory for storing pixel values of previous frames and a read memory for comparing stored pixel values with pixel values of a current frame, are not required, differently from a conventional technique. That is, in the present invention, a single SDRAM (Synchronous Dynamic Random Access Memory) can be used.
The decoder 106 decodes bit streams of pixel values for a previous frame F′n−1 stored in the memory 104 for each block, and outputs the decoded bit streams to the second line buffer 108.
The bit depth decoder 400 decodes first bit depth information representing the number of bits required to binarize coefficients of a transform block, and outputs the decoded first bit depth information to the mode decoder 302. For example, if a first bit depth, which has been set in advance or reset when encoding, is information indicating 9 [bits], the bit depth decoder 400 decodes the first bit depth information.
The mode decoder 402 decodes a bit stream for a division mode to divide the transform block into a first area and a second area, in response to the decoded first bit depth received from the bit depth decoder 400, and outputs the decoded bit stream to the flag information decoder 404. For example, if a bit stream for a division mode generated when encoding is a bit stream for the second division mode shown in
The flag information decoder 404 decodes a bit stream with first flag information indicating that all the coefficients of the first area are within a predetermined value range or a bit stream with second flag information indicating that at least one coefficient of the first area is not within the predetermined value range, in response to the decoded result for the division mode received from the mode decoder 402, and outputs the decoded bit stream to the coefficient decoder 406. For example, since all the coefficients of the first area of the second division mode shown in
The coefficient decoder 406 receives the decoded result of the first flag information or the second flag information from the flag information decoder 404, decodes the bit streams of the coefficients of the transform block, and outputs the decoded bit streams to the second inverse-quantization and inverse-transform unit 408. For example, the coefficient decoder 406 sequentially decodes data “00” and two data “01” which are bit streams for the coefficients of the first area shown in
The second inverse-quantization and inverse-transform unit 408 inverse-quantizes and inverse-transforms the decoded coefficients of the transform block received from the coefficient decoder 406, and outputs the inverse-quantized and inverse-transformed results to the second RGB signal decoder 410.
The second RGB signal decoder 410 receives and decodes a RGB signal of the inverse-quantized and inverse-transformed results from the second inverse-quantization and inverse-transform unit 408 and outputs the decoded RGB signal to the second spatial image prediction compensator 412.
The second spatial image prediction compensator 412 receives the decoded RGB signal from the second RGB signal decoder 410 and compensates for spatially predicted pixel values of the block whose RGB signal is decoded.
Returning to
The compensation pixel value detector 110 detects compensation pixel values for respective pixels, using pixel value differences between the pixel values of the current frame Fn stored in the first line buffer 100 and the pixel values of the previous frame F′n−1 stored in the second line buffer 108. For example, if a pixel value of a specific pixel of a current frame Fn is “128” and a pixel value of a corresponding specific pixel of a previous frame F′n−1 is “118”, the pixel compensation value detector 110 detects a compensation pixel value 178 (128+50=178) obtained by adding the current pixel value with a compensation value (for example, 50) corresponding to “10” which is a difference between the two pixel values. The compensation pixel value detector 110 stores a look-up table including compensation values corresponding to pixel value differences between pixel values of a current frame Fn and pixel values of a previous frame F′n−1.
Hereinafter, a method for performing DCC of a LCD, according to the present invention, will be described with reference to the appended drawings.
Referring to
Then, the pixel values stored for each line are transformed and quantized for each block, thereby generating bit streams (operation 502).
Referring to
After operation 600, redundant information is removed from the R, G, and B pixel values of the current block, and a RGB signal from which redundant information is removed is encoded (operation 602). When pixel values are directly spatially predicted for R, G, and B colors of an RGB image, redundant information is removed using correlation of the spatially predicted pixel values for the R, G, and B colors and a RGB signal from which the redundant information is removed is encoded.
After operation 602, the pixel values of the pixels of the block are transformed and quantized (operation 604). The pixel values are generally transformed using orthogonal transform encoding, for example, Discrete Cosine Transform (DCT). Here, the transformed and quantized block is referred to as a transform block
After operation 604, a division mode for dividing the transform block into a first area in which at least one coefficient is not “0” and a second area in which all coefficients are “0”, along a predetermined diagonal line, is decided (operation 606). The division mode is used to divide the transform block into an area in which all coefficients are “0” and an area in which at least one coefficient is not “0”.
In a 4×4 transform block as shown in
In a 4×4 transform block as shown in
After operation 606, a second bit depth representing the number of binarized bits of each coefficient of a first area is decided according to whether all coefficients of the first area are within a predetermined value range (operation 608). The second bit depth means the number of bits used for binarizing the coefficients of the first area. Table 1 is a look up table representing second bit depths corresponding to predetermined value ranges.
First, it is determined whether all coefficients of a first area are within a predetermined value range (operation 700).
If all the coefficients of the first area are within the predetermined value range, first flag information indicating that all the coefficients of the first area are within the predetermined value range is set (operation 702). Referring to
After operation 702, a second bit depth is decided in response to the set first flag information (operation 704). The second bit depth is decided according to the type of a division mode and a predetermined value range. Also, the second bit depth can be decided regardless of the type of the division mode.
In operation 700, if one or more of the coefficients of the first area is not within the predetermined value range, second flag information indicating that at least one of the coefficients of the first area is not within the predetermined value range is set (operation 706). Referring to
Meanwhile, after operation 608, it is determined whether adjustment of a compression rate of a transform block is requested (operation 610).
If adjustment of the compression rate of the transform block is requested, a first bit depth indicating the number of binarized bits of each coefficient of the transform block is reset and the process proceeds to operation 600 (operation 612). The first bit depth means the number of bits used to binarize each coefficient of the transform block. The first bit depth is reset using a quantization adjustment value for adjusting a quantization period. Table 2 lists first bit depths corresponding to quantization adjustment values.
However, if adjustment of the compression rate of the transform block is not requested, bit streams of the coefficients of the first area are generated according to a decided division mode and a second bit depth (operation 614). At this time, if all the coefficients of the transform block are “0”, only a bit stream for identification information of the division mode is generated. Also, if the total number of bits used when the bit streams for all the coefficients of the first area are generated is equal to or greater than the total number of bits used when bit streams for all the pixel values of the block are generated, the bit streams for the pixel values of the block are generated.
Meanwhile, operation 608 can be omitted. If operation 608 is omitted, in operation 614, the bit streams for the coefficients of the first area are generated according to the decided division mode and the predetermined first bit depth. Although operation 608 is performed, if no second bit depth is decided due to setting of the second flag information, in operation 614, the bit streams for the coefficients of the first area are generated according to the decided division mode and the predetermined first bit depth.
After operation 502, the generated bit streams are stored (operation 504). In the present invention, a single memory is used as a write memory for storing pixel values of previous frames and as a read memory for comparing stored pixel values with current pixel values, differently from the conventional technique.
After operation 504, the stored bit streams are decoded for each block (operation 506).
A block in which pixel values are transformed and quantized is hereinafter referred to as a transform block. Referring to
After operation 800, information of bit streams for a division mode for dividing the transform block into a first area in which at least one of the coefficients of the transform block is not “0” and a second area in which all the coefficients of the transform block are “0”, along a predetermined diagonal line, is decoded (operation 802).
After operation 802, a bit stream of first flag information indicating that all the coefficients of the first area are within a predetermined value range is decoded, or a bit stream of second flag information indicating that at least one of the coefficients of the first area is not within the predetermined value range is decoded (operation 804).
After operation 804, information of bit streams for the coefficients of the transform block is decoded (operation 806).
After operation 806, the decoded coefficients are inverse-quantized or inverse-transformed (operation 808).
After operation 808, a RGB signal of the inverse-quantized and inverse-transformed block is decoded (operation 810).
After operation 810, spatially predicted pixel values for the block whose RGB signal is decoded are compensated for when encoding (operation 812).
Meanwhile, after operation 508, the decoded pixel values are read and temporarily stored for each block (operation 508).
After operation 508, compensation pixel values for the respective pixels are detected from pixel value differences between the pixel values of the current frame stored in operation 500 and the pixel values of the previous frame stored in operation 508 (operation 510).
As described above, in an apparatus and method for performing dynamic capacitance compensation (DCC) in an LCD, according to the present invention, it is possible to reduce the number of memories for storing pixel values of image data, required to perform the DCC for improving a response speed of a LCD.
Also, in an apparatus and method for performing DCC of a LCD, according to the present invention, it is possible to reduce the number of pins of a memory interface by reducing the number of memories, resulting in minimizing a chip size.
Also, in an apparatus and method for performing DCC of a LCD, according to the present invention, it is possible to enhance compression efficiency without visual deterioration in images.
Also, in an apparatus and method for performing DCC in an LCD, according to the present invention, it is possible to easily perform real-time encoding and decoding for images.
Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2004-0091850 | Nov 2004 | KR | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 6181823 | Takahashi | Jan 2001 | B1 |
| Number | Date | Country | |
|---|---|---|---|
| 20060098879 A1 | May 2006 | US |
