Patent Application
20060139287
This application claims the priority of Korean Patent Application No. 10-2004-0115072, filed on Dec. 29, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein 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 a DCC compensation apparatus and method for an LCD, which can easily process image data in real time, reduce the number of memories, and hardly suffer from degradation of image quality.
2. Description of Related Art
A liquid crystal display (LCD) injects a liquid crystal between two sheets of glass, applies electrical pressure thereto, and displays characters/images using optical changes that occur when the sequence of the crystal liquid molecules is changed by the electrical pressure. LCDs operate on 1.5V-2V and are widely used in watches, calculators, and laptop computers due to low power consumption.
One of the disadvantages of LCDs is slow response time. The slow response time causes values of previous and current images to be combined, resulting in a blurring phenomenon. Generally, one frame lasts approximately 16.7 ms. When voltage is applied to both ends of liquid crystal material, it takes time for the liquid crystal material to respond. Therefore, time delay is required to express a desired pixel value and such time delay causes blurring.
To improve response time of LCDs, a dynamic capacitance compensation (DCC) method is used. In DCC, the difference between a pixel value of a previous frame and a pixel value of a current frame is calculated, a value proportional to the difference to the pixel value of the current frame is added, and the result of addition is outputted. To perform DCC, pixels values of the previous frame must be stored in a memory.
However, a writing memory for storing the pixel values of the previous frame and a reading memory for reading the stored pixel values are required to store the pixel values of the previous frame without compression. In other words, independent writing and reading memories must be installed to smoothly perform the DCC by storing the uncompressed pixel values of the previous frame in the writing and reading memories.
To relieve the burden of having to install two or more memories, compressing image data may be considered. In other words, a bit stream of the pixel values of the previous frame is compressed using an encoder and stored in a memory, and the compressed bit stream is decoded using a decoder. Then, the pixel values of the previous frame are compared with the pixel values of the current frame to perform the DCC.
A color sampling compression method has been used to compress pixel values of a previous frame. In the color sampling compression method, the pixel values of the previous frame are compressed through YcbCr conversion and down-sampling processes. Here, Y denotes luminance, and Cb and Cr denote chrominance. However, the color sampling compression method changes color and has poor compression efficiency.
In this regard, to perform the DCC, conventional LCDs store the pixel values of the previous frame without compression or compress the pixel values of the previous frame through the color sampling compression, running the risk of compromising image quality.
An aspect of the present invention provides a dynamic capacitance compensation (DCC) apparatus of a liquid crystal display (LCD), which can encode and decode image data in line units.
An aspect of the present invention also provides a DCC compensation method for an LCD, which can encode and decode image data in line units.
According to an aspect of the present invention, there is provided a dynamic capacitance compensation (DCC) apparatus for a liquid crystal display (LCD), the apparatus including: a one-dimensional block-encoding unit reading pixel values of an image in line units, dividing the pixel values of the read image into one-dimensional blocks in predetermined pixel units, transforming and quantizing the one-dimensional blocks, and generating bit streams; a memory storing the generated bit streams; a one-dimensional block-decoding unit which decodes the bitstreams stored in the memory by inverse quantization and inverse transform; and a compensation pixel value-detecting unit detecting a compensation pixel value for each pixel based on a difference between each pixel value of a current frame and each pixel value of a previous frame decoded by the one-dimensional block-decoding unit.
According to another aspect of the present invention, there is provided a dynamic capacitance compensation (DCC) method for a liquid crystal display (LCD), the method including: reading pixel values of an image in line units, dividing the pixel values of the read image into one-dimensional blocks in predetermined pixel units, transforming and quantizing the one-dimensional blocks, and generating bit streams; storing the generated bit streams in a memory; inversely quantizing and inversely transforming the bit streams stored in the memory and decoding the inversely quantized and inversely transformed bit streams; and detecting a compensation pixel value for each pixel based on a difference between each pixel value of a current frame and each pixel value of a previous frame.
According to another embodiment of the present invention, there is provided a method of improving a response time of a liquid crystal display using dynamic capacitance compensation, the method including: reading pixel values of an image in line units, dividing the read pixel values into one-dimensional blocks in predetermined pixel units, transforming and quantizing the one-dimensional blocks, and generating bit streams; storing the generated bit streams; inversely quantizing and inversely transforming the stored bit streams and decoding the inversely quantized and inversely transformed bit streams; and detecting a compensation pixel value for each pixel of the decoded bit streams based on a difference between each pixel value of a current frame and each pixel value of a previous frame.
Additional and/or other aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
The above and/or other aspects and advantages of the present invention will become apparent and more readily appreciated from the following detailed description, taken in conjunction with the accompanying drawings of which:
Reference will now be made in detail to 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 in order to explain the present invention by referring to the figures.
The one-dimensional block-encoding unit 100 reads pixel values of an image in line units, divides the pixel values in predetermined pixel units into one-dimensional blocks, transforms and quantizes the one-dimensional blocks, and generates bit streams. One-dimensional blocks refer to blocks into which pixel values of an image read in line units are divided in predetermined pixel units.
The one-dimensional block-encoding unit 100 reads pixel values of a current frame Fn in line units, divides the pixel values in 4 or 8 pixel units into one-dimensional blocks, encodes the one-dimensional blocks, and outputs the encoded one-dimensional blocks to the first buffer 102.
The spatial predictor 200 spatially predicts pixel values of a one-dimensional block using blocks adjacent to the one-dimensional block and outputs the spatially predicted pixel values to the RGB signal encoder 202. The process of removing spatial redundancy of a one-dimensional block using blocks spatially adjacent to the one-dimensional block is called spatial prediction (referred to as intra prediction). In other words, spatially predicted pixel values are obtained by estimating a prediction direction based on blocks adjacent to a one-dimensional block for each R, G and B color component. The spatial predictor 200 removes spatial redundancy between a current block and its adjacent blocks using the result of spatial prediction compensation output from the first spatial prediction compensator 210, that is, using restored blocks in a current image.
In particular, the spatial predictor 200 spatially predicts a one-dimensional block using only pixel values of blocks in a row above a row where the one-dimensional block is.
When determining a spatial prediction direction using blocks adjacent to a one-dimensional block, the prediction direction determiner 300 determines the spatial prediction direction using pixel values of blocks in a row above a row where the one-dimensional block is and outputs the determined spatial prediction direction to the pixel value filter 302.
Referring to
Referring to
In a right diagonal direction, the differences between the pixel values of the 4×1 one-dimensional block and the pixel values of the block in the row above the row where the 4×1 one-dimensional block exists are a′=a-P, b′=b-A, c′=c-B, and d′=d-C, respectively. It is assumed that sums of the differences in the right diagonal direction for the R, G and B components are S4, S5, and S6, respectively.
In a left diagonal direction, the differences between the pixel values of the 4×1 one-dimensional block and the pixel values of the block in the row above the row where the 4×1 one-dimensional block exists are a′=a-B, b′=b-C, c′=c-D, and d′=d-E, respectively. It is assumed that sums of the differences in the left diagonal direction for the R, G and B components are S7, S8, and S9, respectively.
Prediction directions having minimum sums for the R, G and B components are determined as spatial prediction directions for the R, G and B components, respectively. In other words, a prediction direction having a minimum value among S1, S4, and S7 is determined as the prediction direction for the component R. Likewise, a prediction direction having a minimum value among S2, S5, and S8 is determined as the prediction direction for the component G. A prediction direction having a minimum value among S3, S6, and S9 is determined as the prediction direction for the component B.
In a second method, the prediction direction determiner 300 calculates sums of the differences between the pixel values of the 4×1 one-dimensional block and the pixel values of the block in the row above the row where the 4×1 one-dimensional block is, and calculates a direction determination value in consideration of a compression rate for each direction. The prediction direction determiner 300 determines a direction having a minimum value among the calculated direction determination values as a spatial prediction direction. The prediction direction determiner 300 obtains direction determination values using
C=D+λR, (1)
where C denotes a direction determination value for each direction, D denotes a sum of differences between pixel values of a current block and pixel values of a block adjacent to the current block for each direction, λ denotes a predetermined constant value, and R denotes a compression rate for each direction.
In a third method, the prediction direction determiner 300 calculates the sums of the differences between the pixel values of the 4×1 one-dimensional block and the pixel values of the block in the row above the row where the 4×1 one-dimensional block is for the respective R, G and B components. Then, the prediction direction determiner 300 calculates sums of the sums of the differences for the R, G and B components and determines a prediction direction having a minimum sum among the sums of the sums of the differences as a direction for spatial prediction.
For example, as illustrated in
When calculating a sum of the sums of the differences for the respective R, G and B components, a different weight may be given to each of the R, G and B components. For example, when S1 is a sum of the differences between the pixel values of the 4×1 one-dimensional block and the pixel values of the block in the row above the row where the 4×1 one-dimensional block is for the component R, S2 is a sum of the differences for the component G, and S3 is a sum of the differences for the component B, a sum of S1, S2, and S3 may be calculated by applying different weights to S1, S2, and S3. In other words, the sum of S1, S2, and S3 may be SV=0.3□S1+0.6□S2+0.1□S3. The reason why different weights are given to S1, S2, and S3 is that the processing of the component G is important to an image. The weights described above are merely examples, and various weights can be applied to S1, S2, and S3.
In a fourth method, the prediction direction determiner 300 calculates the sums of the differences between the pixel values of the 4×1 one-dimensional block and the pixel values of the block in the row above the row where the 4×1 one-dimensional block is for the respective R, G and B components and obtains a direction determination value in consideration of a compression rate for each direction. The prediction direction determiner 300 determines a direction having a minimum value among the obtained direction determination values as a spatial prediction direction. The prediction direction determiner 300 obtains direction determination values using Equation 1 described above.
The pixel value filter 302 filters the pixel values of the blocks in the row above the row where the one-dimensional block is and outputs the filtered pixel values to the spatial predictor 304. Such filtering is required to prevent degradation of image quality caused by the spatial prediction performed using only the pixel values of the blocks in the row above the row where the one-dimensional block is.
A filtering method will now be described with reference to
Other pixel values of the blocks in the row above the row where the one-dimensional block is are also filtered as described above. The filtering method described above is just an example, and pixel values of more adjacent blocks may be used in the filtering process.
The pixel value predictor 304 spatially predicts the pixel values of the one-dimensional block using only the blocks in the row above the row where the one-dimensional block is. For example, the pixel value predictor 304 spatially predicts the pixel values of the one-dimensional block in one of the vertical direction, the right diagonal direction, and the left diagonal direction determined by the prediction direction determiner 300.
As shown in
Returning to
The transformer/quantizer 204 transforms and quantizes pixel values of each one-dimensional block, and outputs the converted and quantized spatially predicted pixel values to the first inverse quantizer/inverse transformer 206 and the mode determiner 212. Orthogonal transform encoding is used to convert spatially predicted pixel values of each one-dimensional block. In the orthogonal transform encoding, a fast Fourier transform (FFT), a discrete cosine transform (DCT), a Karhunen-Loeve transform (KLT), a Hadamard transform, and a slant transform are widely used.
In particular, the transformer/quantizer 204 of the present invention uses the Hadamard transform. In the Hadamard transform, a Hadamard matrix composed of +1 and −1 is used to convert pixel values.
The first inverse quantizer/inverse transformer 206 receives the transformed/quantized spatially predicted pixel values from the transformer/quantizer 204, inversely quantizes/inversely transforms transformed and quantized coefficients of a one-dimensional conversion block, and outputs the inversely quantized/inversely transformed coefficients to the first RGB signal decoder 208.
The first RGB signal decoder 208 receives the inversely quantized/inversely transformed coefficients from the first inverse quantizer/inverse transformer 206, decodes an RGB signal of the one-dimensional conversion block, and outputs the decoded RGB signal to the first spatial prediction compensator 210.
The first spatial prediction compensator 210 receives the decoded RGB signal from the first RGB signal decoder 208, compensates for the spatially predicted pixel values of the one-dimensional conversion block, and outputs the compensated spatially predicted pixel values of the one-dimensional conversion block to the spatial predictor 200.
The mode determiner 212 determines a division mode for dividing the one-dimensional conversion block into a first region where at least one of the coefficients of the one-dimensional conversion block is not “0” and a second region where all of the coefficients are “0.” The mode determiner 212 outputs the result of determination to the bit depth determination controller 214.
The division mode is for dividing the one-dimensional conversion block into a region where the coefficients of the one-dimensional conversion block are “0” and a region where the coefficients of the one-dimensional conversion block are not “0.”
Referring to
Returning to
The bit depth determination controller 214 receives a division mode determined by the mode determiner 212 and determines a second bit depth indicating the number of bits used to binarize coefficients of the first region, based on whether all of the coefficients of the first region are within a predetermined range. Then, the bit depth determination controller 214 outputs the determined second bit depth to the bit depth resetter 216.
A bit depth refers to the number of bits used to store information regarding each pixel in computer graphics. Thus, the second bit depth denotes the number of bits used to binarize coefficients of the first region. A range of coefficients is pre-determined.
Table 1 below is a lookup table that shows the second bit depth determined according to a range of coefficients.
If it is assumed that the division mode identification information in Table 1 indicates identification information of each of the second and third division modes in an 8×1 one-dimensional conversion block, the identification information of the second division mode is “1” and the identification information of the third division mode is “2.” The first division mode, i.e., the skip mode, is not shown in Table 1 since the bit stream generator 218, which will be described later, does not generate bit streams for coefficients.
The bit depth determination controller 214 stores information needed to determine the second bit depth in a memory. The information may be a lookup table like Table 1.
The coefficient range determiner 400 determines whether all of coefficients of the first region are within a predetermined range and outputs the result of determination to the flag information setter 402. For example, it is assumed that a predetermined range of coefficients of the first region is “−4 through 3” as shown in Table 1 and that a division mode determined by the mode determiner 212 is the second division mode (here, it is assumed that the identification information of the second division mode is “1”). The coefficient range determiner 400 determines whether the coefficients of the first region of the second division mode are within the predetermined range of “−4 through 3.”
The flag information setter 402 sets first flag information indicating that all of the coefficients of the first region are within the predetermined range, in response to the result of determination made by the coefficient range determiner 400 and outputs the first flag information to the bit depth determiner 404.
The flag information setter 402 sets second flag information indicating that at least one of the coefficients of the first region is not within a predetermined range and outputs the second flag information to the bit depth resetter 216 via an output node OUT1. For example, it is assumed that the predetermined range of the coefficients of the first region is “−4 through 3” as shown in Table 1 and that a division mode determined by the mode determiner 212 is the second division mode (here, it is assumed that the identification information of the second division mode is “1”).
Referring to
Referring to
The bit depth determiner 404 also determines the second bit depth according to the type of division mode determined by the mode determiner 212. For example, if the first flag information is set, the bit depth determiner 404 determines “3 bits,” which correspond to the second division mode whose identification mode is “1” (see Table 1), as the second bit depth. The bit depth determiner 404 may also determine a specific bit depth as the second bit depth regardless of the type of division mode.
The bit depth resetter 216 identifies a need for adjusting a compression rate of the one-dimensional conversion block, in response to the second bit depth determined by the bit depth determination controller 214. If the bit depth resetter 216 identifies the need for adjusting the compression rate of the one-dimensional conversion block, the bit depth resetter 216 resets first bit depth and outputs the reset first bit depth to the converter/quantizer 204. The first bit depth denotes the number of bits used to binarize coefficients of a one-dimensional conversion block. The bit depth resetter 216 resets the first bit depth using a quantization adjustment value for adjusting a quantization interval.
The transformer/quantizer 204 transforms and quantizes pixel values of the one-dimensional conversion block in response to the first bit depth reset by the bit depth resetter 216. If the bit depth resetter 216 does not identify the need for adjusting the compression rate, the bit depth resetter 216 outputs the determined division mode and second bit depth to the bit stream generator 218.
Table 2 below shows first bit depths corresponding to quantization adjustment values.
As shown in Table 2, the greater the quantization value, the smaller the first bit depth. A small first bit depth denotes that a small number of bits are used to binarize coefficients of a one-dimensional conversion block. Since a small number of bits are used to express the coefficients when the first bit depth is small, a small first bit depth is translated into a high compression rate.
Hence, if the quantization adjustment value is raised, thereby making the first bit depth smaller, the compression rate can be raised. However, image quality may be degraded due to the raised compression rate. Conversely, if the quantization adjustment value is lowered, thereby making the first bit depth larger, the compression rate can be lowered.
The bit stream generator 218 generates bit streams for coefficients of the first region according to the determined division mode and second bit depth. For example, if a predetermined range of coefficients of the first region is “−4 through 3” as shown in Table 1 and a division mode determined by the mode determiner 212 is the second division mode, the second bit depth is determined as “3 bits” as shown in Table 1.
If all of the coefficients of the one-dimensional conversion block are “0,” the bit stream generator 218 generates a bit stream only for identification information of a division mode. For example, referring to
When the type of mode is divided into three modes, each mode can be expressed using 2 bits. Therefore, a bit stream for “0,” which is the identification information of the first division mode, is “00.”
Also, if the number of bits required to generate bit streams for coefficients of the first region is greater than or equal to the number of bits required to generate bit streams for pixel values of a one-dimensional block, the bit stream generator 218 generates the bit streams for the pixel values of the one-dimensional block. For example, when an 8×1 block before being transformed/quantized has pixel values having a bit depth of 8 bits, if bit streams for the pixel values of the 8×1 block are generated without compressing the pixel values, the total number of bits is “8×8=64 bits.” Therefore, when the total number of bits of the coefficients of the first region, which will be generated according to the first bit depth or the second bit depth, is 64 bits or greater, the bit stream generator 218 does not generate bit streams for transformed/quantized coefficients and generates bit streams for the pixel values of the one-dimensional block before being transformed/quantized.
The bit stream generator 218 may generate bit streams for coefficients of the first region according to the determined division mode and predetermined first bit depth. For example, it is assumed that the predetermined range of the coefficients of the first region is “−4 through 3” as shown in Table 1 and that a division mode determined by the mode determiner 212 is the second division mode.
The bit stream generator 218 may generate bit streams for the coefficients of the one-dimensional conversion block using a variable length coding method. In the variable length coding method, short bit streams are generated for coefficients that occur in high probability and long bit streams are generated for coefficients that occur in low probability.
In particular, when generating bit streams for the coefficients of the first region, the bit stream generator 218 divides the coefficients of the first region into a first coefficient and the remaining coefficients and generates bit streams using the variable length coding method.
For example, when the first coefficient of the first region is “0” as shown in
Also, when absolute values of the coefficients excluding the first coefficient of the first region are “1,” the bit stream generator 218 encodes the coefficients into “0.” When the absolute values of the coefficients excluding the first coefficient of the first region are “0,” the bit stream generator 218 encodes the coefficients into “10.” However, if the absolute values of the coefficients excluding the first coefficient of the first region are “0” nor “1,” the bit stream generator 218 encodes the coefficients into “11,” generates bit streams for the coefficients excluding the first coefficient of the first region according to the determined division mode and the first or second bit depth, and add the bit stream behind “11.”
The bit stream generator 218 encodes “+ (positive sign)” into “0” and encodes “− (negative sign)” into “1” in order to encode “+ (positive sign” and − (negative sign)” of coefficients of the first region, and adds “0” and “1” to the encoded bit streams of the coefficients.
The bit stream generator 218 may generate bit streams for identification information of a prediction direction mode using the variable length coding method. For example, if each spatial prediction direction is defined as a prediction direction mode, the bit stream generator 218 may encode a vertical prediction direction mode into “0”, a right diagonal prediction direction mode into “10,” and a left diagonal prediction direction mode into “11.”
Generating bit streams for coefficients of the first region or prediction direction modes using the variable length coding method described above is just an example. Bit streams for the coefficients of the first region may be generated using diverse methods.
Returning to
The memory 104 stores the bit stream of the predetermined size received from the first buffer 102. In particular, since the memory 104 of the present invention compresses image data before storing the image data, a large memory capacity is not required. In other words, in the present invention, it is not necessary to separately implement a writing memory for storing pixel values of a previous frame and a reading memory for comparing pixel values of a current frame with the stored pixel values of the previous frame. Hence, the memory 104 used in the present invention may include only one synchronous dynamic random access memory (SDRAM).
The second buffer 106 receives and temporarily stores the bit stream of the predetermined size stored in the memory 104 and outputs the temporarily stored bit stream of the predetermined size to the one-dimensional block decoder 108 in one-dimensional block units. The second buffer 106 divides the bit stream of the predetermined size stored in the memory 104 in one-dimensional block units and transmits the divided bit stream to the one-dimensional block-decoding unit 108.
The one-dimensional block-decoding unit 108 decodes a bit stream for pixel values of a previous frame F′n-1 received from the second buffer 106 in one-dimensional block units by inversely quantizing/inversely transforming the bit stream for the pixel values of the previous frame F′n-1 and outputs the decoded bit stream to the compensation pixel value-detecting unit 110.
The bit depth decoder 500 decodes information of the first bit depth indicating the number of bits used to binarize coefficients of a one-dimensional conversion block and outputs the decoded information to the mode decoder 502. For example, if the first bit depth predetermined or reset in the encoding process has information indicating “9 bits,” the bit depth decoder 500 decodes the information indicating that the first bit depth is “9 bits.”
In response to the decoded information of the first bit depth received from the bit depth decoder 500, the mode decoder 502 decodes information regarding a bit stream for a division mode dividing the one-dimensional conversion block into the first region where at least one of coefficients of the one-dimensional conversion block is not “0” and the second region where all of the coefficients are “0,” and outputs the decoded information to the flag information decoder 504. For example, if a bit stream for a division mode generated in the encoding process are a bit stream for the second division mode of
After receiving the decoded information of the division mode from the mode decoder 502, the flag information decoder 504 decodes the bit stream for the first flag information indicating that all of coefficients of the first region are within a predetermined range or a bit stream for the second flag information indicating that at least one of the coefficients of the first region is not within the predetermined range and outputs the decoded bit stream to the coefficient decoder 506.
For example, in the second division mode of
Also, in the second division mode of
The coefficient decoder 506 receives the decoded first or second flag information from the flag information decoder 504, decodes information of the bit streams for the coefficients of the one-dimensional conversion block, and outputs the decoded information to the second inverse quantizer/inverse transformer 508. For example, the coefficient decoder 506 sequentially decodes “000,” “001,” and “001,” which are bit streams for the coefficients of the first region of
The second inverse quantizer/inverse transformer 508 inversely quantizes and inversely transforms the coefficients of the one-dimensional conversion block received from the coefficient decoder 506 and outputs the inversely quantized/inversely transformed coefficients of the one-dimensional conversion block to the second RGB signal decoder 510. The inverse quantization/inverse transform of the coefficients of the one-dimensional conversion block is performed as a reverse process of the transform/quantization process. In particular, the second inverse quantizer/inverse transformer 508 inversely transforms the transformed coefficients of the one-dimensional conversion block using the Hadamard transform method.
The second RGB signal decoder 510 receives the inversely quantized/inversely transformed coefficients from the second inverse quantizer/inverse transformer 508, decodes an RGB signal of the inversely quantized/inversely transformed block, and outputs the RGB signal to the second spatial prediction compensator 512.
The second spatial prediction compensator 512 receives the decoded RGB signal from the second RGB signal decoder 510 and compensates for the spatially predicted pixel values of the inversely quantized/inversely transformed block having the decoded RGB signal. In particular, the second spatial prediction compensator 512 compensates for the spatially predicted pixel values of the one-dimensional block using only the pixel values of the blocks in the row above the row where the one-dimensional block is.
The compensation pixel value-detecting unit 110 detects a compensation pixel value for each pixel, based on a difference between a value of a pixel of the current frame Fn and a value of a pixel of the previous frame F′n-1 decoded by the one-dimensional block-decoding unit 108. For example, if a pixel value of the current frame Fn is “128” and a pixel value of the previous frame F′n-1 is “118,” the compensation pixel value-detecting unit 110 detects a compensation pixel value “128+50=178,” which is obtained by adding a compensation value (for example, 50) corresponding to the difference between the two pixel values, i.e., “10,” to the pixel value of the current frame Fn. The compensation pixel value-detecting unit 110 stores compensation values respectively corresponding to the differences between pixel values of the current frame Fn and the pixel values of the previous frame F′n-1 in a lookup table.
A DCC method for an LCD according to the present invention will now be described with reference to the attached drawings.
In particular, sums of differences between pixel values of a one-dimensional block and pixel values of blocks in a row above a row where the one-dimensional block is are calculated for the respective R, G and B components and a prediction direction having a minimum sum among sums of the sums of the differences for the R, G and B components is determined as a spatial prediction direction. Since the methods of determining the spatial prediction direction have been described above, their detailed descriptions will be omitted.
After operation 800, the pixel values of the blocks in the row above the row where the one-dimensional block is are filtered (operation 802). Such filtering is required to prevent degradation of image quality caused by the spatial prediction performed using only the pixel values of the blocks in the row above the row where the one-dimensional block is. The method of filtering pixel values of blocks in a row above a row where a one-dimensional block is has been described above, and thus its detailed description will be omitted.
After operation 802, the pixel values of the one-dimensional block are spatially predicted using only the pixel values of the blocks in the row above the row where the one-dimensional block is (operation 804). The pixel values of the one-dimensional block are spatially predicted in a direction determined in operation 800 as the spatial prediction direction among the vertical direction, the right diagonal direction, and the left diagonal direction. Since the methods of determining the spatial prediction direction have been described above, their detailed descriptions will be omitted.
After operation 700, redundant information is removed from the spatially predicted pixel values of the one-dimensional block for each of the R, G and B components, and an RGB signal having the redundant information removed is encoded (operation 702). When pixel values are spatially predicted for each of the R, G and B color components of an RGB image, redundant information is removed using the correlation between the spatially predicted pixel values for each of the R, G and B components, and an RGB signal without the redundant information is encoded.
After operation 702, pixel values of the one-dimensional block are transformed and quantized (operation 704). In particular, in the present embodiment, the Hadamard transform, which is one kind of orthogonal transform encoding, is used. In the Hadamard transform, a Hadamard matrix composed of +1 and −1 is used to transform pixel values.
After operation 704, a division mode for dividing a one-dimensional conversion block, i.e., the transformed/quantized one-dimensional block, into a first region where at least one of the coefficients of the one-dimensional conversion block is not “0” and a second region where all of the coefficients are “0” is determined (operation 706). The division mode is for dividing the one-dimensional conversion block into a region where the coefficients of the one-dimensional conversion block are “0” and a region where the coefficients of the one-dimensional conversion block are not “0.”
After operation 706, a second bit depth indicating the number of bits used to binarize coefficients of the first region is determined based on whether all of the coefficients of the first region are within a predetermined range (operation 708). The second bit depth denotes the number of bits used to binarize coefficients of the first region. Table 1 is a lookup table that shows the second bit depth determined according to a value range.
In operation 1000, if it is determined that at least one of the coefficients of the first region is not within the predetermined range, second flag information indicating that at least one of the coefficients of the first region is not within the predetermined range is set (operation 1006). Since a method of setting the second flag information has been described above, its detailed description will be described.
Returning to
However, if the need for adjusting the compression rate of the one-dimensional conversion block is not identified, bit streams for coefficients of the first region are generated according to the determined division mode and second bit depth (operation 714). If all of the coefficients of the one-dimensional conversion block are “0,” bit streams are generated only for identification information of a division mode. In addition, if the number of bits required to generate bit streams for coefficients of the first region is greater than or equal to the number of bits required to generate bit streams for the pixel values of the one-dimensional block, the bit streams for the pixel values of the one-dimensional block are generated.
Since operation 708 is not necessarily required in the present embodiment, operation 708 may be omitted. If operation 708 is omitted, a bit stream for the coefficients of the first region is generated according to the determined division mode and first bit depth in operation 714. If operation 708 is not omitted, when the second flag information is set but the second bit depth is not set, a bit stream for the coefficients of the first region is also generated according to the determined division mode and first bit depth in operation 714.
Bit streams for the coefficients of the one-dimensional conversion block may be generated using a variable length coding method. In the variable length coding method, short bit streams are generated for coefficients that occur in high probability and long bit streams are generated for coefficients that occur in low probability.
In particular, when generating bit streams for coefficients of the first region, the coefficients of the first region are divided into a first coefficient and the remaining coefficients and then bit streams are generated using the variable length coding method.
Bit streams for identification information of a prediction direction mode can also be generated using the variable length coding method. Since the method of generating bit streams using the variable length coding method has been described above, its detailed description will be omitted.
Returning to
After operation 602, the bit stream of the predetermined size is stored in the memory (operation 604). In particular, in the present invention, since image data is compressed before being stored, a large memory capacity is not required. In other words, in the present embodiment, it is not necessary to separately implement a writing memory for storing pixel values of a previous frame and a reading memory for comparing pixel values of a current frame with the stored pixel values of the previous frame. Hence, the memory used in the present embodiment may include only one SDRAM.
After operation 604, the bit stream of the predetermined size stored in the memory 104 is temporarily stored, and the bit stream of the predetermined size is output in one-dimensional block units (operation 606).
After operation 606, the bit stream received in one-dimensional block units is inversely quantized/inversely converted and decoded (operation 608).
After operation 900, information of bit streams for the division mode dividing the one-dimensional conversion block into the first region where at least one of the coefficients of the one-dimensional conversion block is not “0” and the second region where all of the coefficients of the one-dimensional conversion block are “0” is decoded (operation 902).
After operation 902, bit streams for the first flag information indicating that all of coefficients of the first region are within a predetermined range or bit streams for the second flag information indicating that at least one of the coefficients of the first region is not within the predetermined range are decoded (operation 904).
After operation 904, information of the bit stream for the coefficients of the one-dimensional conversion block is decoded (operation 906). In particular, if the bit stream for the coefficients of the one-dimensional conversion block is generated using the variable length coding method, the coefficients of the one-dimensional conversion block are decoded as a reverse process of the variable length coding method.
After operation 906, the coefficients of the one-dimensional conversion block are inversely quantized/inversely transformed (operation 908 ). The inverse quantization/inverse transform of the coefficients of the one-dimensional conversion block is performed as a reverse process of the transform/quantization process. In particular, the converted coefficients of the one-dimensional conversion block are inversely transformed using the Hadamard transform method.
After operation 908, an RGB signal of the inversely quantized/inversely transformed block is decoded (operation 910).
After operation 910, spatially predicted pixel values of the inversely quantized/inversely transformed block having the decoded RGB signal are compensated for (operation 912). In particular, the spatially predicted pixel values of the one-dimensional block are compensated for using only pixel values of blocks in the row above the row where the one-dimensional block is.
Returning to
In a DCC apparatus and method for an LCD according to the above-described embodiments of the present invention, when the DCC is performed, image data is encoded and decoded in line units. Thus, the image data can be processed in real time.
In addition, in the DCC apparatus and method for the LCD according to the above-described embodiments of the present invention, when performing the DCC to improve response time, which is one of disadvantages of an LCD, the number of memories for storing pixel values of image data used to perform the DCC can be reduced, thereby saving parts.
In the DCC apparatus and method for the LCD according to the above-described embodiments of the present invention, since the number of memories is reduced, the number of pins of memory interfaces can also be reduced, resulting in a decrease in a chip size.
Also, the DCC apparatus and method for the LCD according to the above-described embodiments of the present invention enhance compression efficiency while avoiding much visual degradation of image quality.
Although a few embodiments of the present invention have been shown and described, the present invention is not limited to the described embodiments. Instead, it would be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2004-0115072 | Dec 2004 | KR | national |
