Video decoder with down conversion function and method for decoding video signal

Abstract

The present invention relates to a video decoder with a down conversion function, and a method for decoding a video signal. According to the video decoder and the method for decoding a video signal of the present invention, a VLD analyzes a received compressed video stream, and extracts motion signals. The bitstream analyzed at the VLD is converted into a macro block through an IQ and IDCT in succession, and a MC makes motion compensation of an up sampled data by using the extracted motion signals. A data from the IDCT and a data from the MC are added, down sampled by an adaptive down sampler, and stored in an external memory. For motion compensation, the adaptive up sampler up samples the data down sampled at the adaptive down sampler, and provides to the MC.

1 . A video decoder comprising: 
 a VLD (Variable Length Decoder) for analyzing a received compressed bitstream;    an IQ (Inverse Quantizer) for inverse quantizing the compressed bitstream analyzed at the VLD;    an IDCT for discrete cosine transform of a data from the IQ;    an MC (Motion Compensator) for making motion compensation of a data up sampled by using motion signals extracted at the VLD;    an adder for adding a data from the IDCT and a data from the MC;    an adaptive down sampler of a matrix for converting a data from the adder to be in conformity with a picture structure of the compressed bitstream, subjecting the data to adaptive down sampling, and storing the data in an external memory in a field basis; and,    an adaptive up sampler of a structure converted into a transposed matrix of a matrix form for up sampling the data down sampled at the adaptive down sampler, and providing to the MC.    
   
   
       2 . A video decoder as claimed in  claim 1 , wherein the compressed bitstream is an MPEG-2 signal.  
   
   
       3 . A video decoder as claimed in  claim 2 , wherein the MPEG-2 signal is a predictive picture signal or a bi-directional picture signal.  
   
   
       4 . A video decoder as claimed in  claim 1 , wherein the video decoder carries out IDCT in 8×8 block units to suit to a MPEG-2 video syntax.  
   
   
       5 . A video decoder comprising: 
 a VLD for analyzing a received compressed bitstream;    an IQ for inverse quantizing the bitstream analyzed at the VLD;    an IDCT for inverse discrete cosine transform of a data from the IQ in macro block units;    an MC for making motion compensation of a data up sampled by using motion vectors, a motion type, and a motion vertical field selection signal extracted at the VLD;    a DCT buffer for separating a data from the IDCT into a top field data and a bottom field data by using a DCT type signal, a picture structure signal, and a progressive sequence signal extracted at the VLD;    an MC buffer for separating a data from the MC into a top field data and a bottom field data by using the DCT type signal, the picture structure signal, and the progressive sequence signal;    a first adder for adding the top field data from the DCT buffer and the top field data from the MC;    a second adder for adding the bottom field data from the DCT buffer and the bottom field data from the MC;    an adaptive down sampler for subjecting added top field data and added bottom field data from above two adders to adaptive down sampling, and storing in an external memory; and,    an adaptive up sampler for up sampling a down sampled data stored in the external memory and providing to the MC.    
   
   
       6 . A video decoder as claimed in  claim 5 , wherein the block is an 8×8 block.  
   
   
       7 . A video decoder as claimed in  claim 5 , wherein the down sampler includes; 
 a down sampling controlling part for controlling down sampling according to received down sampling parameters,    a vertical down sampling part for down sampling a received data in a vertical direction on a data from the adders under the control of the down sampling controlling part,    a temporary buffer for temporary storage of the vertical down sampled data,    a horizontal down sampling part for down sampling a data from the temporary buffer in a horizontal direction under the control of the down sampling controlling part, and    a forwarding multiplexer for forwarding either of the received data and a data from the horizontal down sampling part selectively under the control of the down sampling controlling part.    
   
   
       8 . A video decoder as claimed in  claim 7 , wherein the down sampler reduces each field data from the adders by one of reduction ratios selected from unity, ½, and ¾.  
   
   
       9 . A video decoder as claimed in  claim 8 , wherein the down sampler carries out down sampling only in a horizontal direction when the down sampler reduces an original data by the ½ reduction ratio.  
   
   
       10 . A video decoder as claimed in  claim 5 , wherein the motion compensator and the up sampler includes; 
 a motion vector translator for translating a motion type signal, a motion vector, and a motion vertical field selection signal from the VLD, to obtain a reference memory read address, and a reference pel for prediction,    a horizontal up sampling filter for making a horizontal up sampling by using the motion vector, the reference memory address, and the reference pels for prediction,    a vertical up sampling filter for making a vertical up sampling a data from the horizontal up sampling filter by using the motion vector, and the motion type,    a combiner for combining up sampled field blocks from the vertical up sampling filter into up sampled frame blocks when a frame prediction is used, and    an ½ pel interpolator for interpolating a data from the combiner by ½ pels, and forwarding to the MC_buffer.    
   
   
       11 . A video decoder as claimed in  claim 5 , wherein, when the received bitstream is an intra picture, data from the IDCT is stored in the external memory right away after the data is down sampled.  
   
   
       12 . A video decoder as claimed in  claim 5 , wherein the up sampler includes; 
 an up sampling controlling part for controlling up sampling according to received up sampling parameters,    a horizontal up sampling part for subjecting a data accessed from the external memory to horizontal up sampling under the control of the up sampling controlling part,    a temporary buffer for temporary storage of the horizontal up sampled data,    a vertical up sampling part for subjecting a data from the temporary buffer to vertical up sampling under the control of the up sampling controlling part, and    a forwarding multiplexer for forwarding either the data access by the external memory or a data from the vertical up sampling part under the control of the up sampling controlling part, selectively.    
   
   
       13 . A video decoder as claimed in  claim 12 , wherein the up sampler adjusts extents of up sampling in horizontal and vertical directions according to unity, ½, or ¾ reduction mode.  
   
   
       14 . A video decoder as claimed in  claim 13 , wherein the up sampler carries out up sampling only in a horizontal direction in the ½ reduction mode, and in vertical and horizontal directions in the ¾ reduction mode.  
   
   
       15 . A video decoder as claimed in  claim 13 , wherein, when C 4×8   T  denotes a 4×8 dimension down sampling transposed matrix, and y 4×1  denotes a down sampling pel value, the up sampler of a luminance carries out up sampling by carrying out 2·C 4×8   T ·y 4×1 , and, when y 2×1  denotes a down sampled 2×1 pels, and C 2×4  denotes a down sampling matrix of 2×4 dimension, the up sampler of chrominance carries out up sampling by carrying out X [4×1]   UP 2·C 2×4 ·y 2×1 .  
   
   
       16 . A method for decoding a video signal, comprising the steps of: 
 (a) detecting signals related to a motion and a picture structure signal from a received video sequence;    (b) processing the received video sequence, for providing data of macro block units;    (c) subjecting the data of macro block units to down conversion, and storing in an external memory as a field basis vertical pel structure; and,    (d) subjecting the down converted data stored in the external memory to motion prediction compensation by using the detected motion signals, and the picture structure signal, to obtain a final down converted data.    
   
   
       17 . A method as claimed in  claim 16 , wherein the step (b) includes the steps of, 
 subjecting the video sequence to VLD to obtain DCT coefficients,    subjecting the DCT coefficients to inverse quantizing, and    subjecting inverse quantized coefficients to IDCT, to provide data of the macro block unit.    
   
   
       18 . A method as claimed in  claim 16 , wherein the macro block unit is 8×8 block suitable for MPEG-2.  
   
   
       19 . A method as claimed in  claim 16 , wherein the detected motion related signals includes a motion vector signal, a motion type signal, and a motion vertical field selection signal.  
   
   
       20 . A method as claimed in  claim 16 , wherein the step (d) includes the steps of, 
 making access to pel values in field units from the external memory for the motion compensation,    converting the accessed field unit pel values if the detected picture structure signal is a frame picture, and    making motion prediction compensation on the frame unit pel values.    
   
   
       21 . A method as claimed in  claim 16 , wherein the step (d) includes the steps of, 
 dividing the frame picture signal into a luminance signal and a chrominance signal,    subjecting a luminance data accessed from the external memory to up sampling filtering by using an up sampling matrix of 2·C 4×8   T ·y 4×1  (C 4×8   T  denotes a 4×8 dimension down sampling transposed matrix, and y 4×1  denotes a down sampled pel value), to obtain up sampled top field and bottom field, respectively,    adding the top field and bottom field of the up sampled luminance data together,    subjecting the added luminance signal data to ½ pel prediction, subjecting a chrominance data accessed from the external memory to up sampling filtering by using an up sampling matrix of X [4×1]   UP =2·C 2×4 ·y 2×1  (where C 2×4  denotes a 2×4 dimension down sampling transposed matrix, and y 2×1  denotes a down sampled pel value), to obtain up sampled top field and bottom field, respectively,    adding obtained top field and bottom field of the chrominance data, and    subjecting the added chrominance data to ½ pel prediction.    
   
   
       22 . A method as claimed in  claim 21 , wherein the step of obtaining top fields and bottom fields of the luminance data and the chrominance data, before carrying out up sampling filtering for obtaining ½ pel interpolation, includes the steps of; 
 making access to a macro block of a reduced resolution from the external memory,    taking blocks adjoining to the macro block of the reduced resolution for producing a macro block of an original picture, and    restoring blocks of perfect resolutions in vertical and horizontal directions of the taken adjoining blocks by using up sampling matrices of X [×1]   UP =2·C 4×8   T ·y 4×1  (where C 4×8   T  denotes a 4×8 dimension down sampling transposed matrix, and y 4×1  denotes a down sampled pel value), and X [4×1]   UP =2·C 2×4 ·y 2×1  (where C 2×4  denotes a 2×4 dimension down sampling transposed matrix, and y 2×1  denotes a down sampled pel value).    
   
   
       23 . A method as claimed in  claim 21 , wherein the step of obtaining top fields and bottom fields of the luminance data and the chrominance data, before carrying out up sampling filtering for obtaining ½ pel interpolation, includes the steps of; 
 malting access to a macro block of a reduced resolution from the external memory,    taking blocks adjoining to the macro block of the reduced resolution in a horizontal direction if there is a ½ pel interpolation in the horizontal direction or a horizontal perfect resolution motion vector is not exact multiple of 8, and    up sampling the taken adjoining blocks by using X[ 8 × 1 ] UP =2·C 4×8   T ·y 4×1  (where C 2×4   T  denotes a 4×8 dimension down sampling transposed matrix, and y 4×1  denotes a down sampled pel value).    
   
   
       24 . A method as claimed in  claim 16 , wherein the step (c) includes, when the picture structure signal is for frame picture and it is intended to reduce the picture by 75%, the steps of; 
 dividing the chrominance signal into n×2n sized top field and bottom field, and dividing the luminance signal to 2n×2n top field and bottom field, and    down sampling the chrominance signal by using an equation y [2×1] =C 2×4 ·X 4×1  (where C 2×4  denotes a down sampling matrix of 2×4 dimension, and y 4×1  denotes 4×1 pels), and down sampling the luminance signal by using an equation y [4×1 ]=C 4×8 ·X 8×1  (where C 4×8  denotes a down sampling matrix of 4×8 dimension, and X 8×1  denotes 8×1 pels).    
   
   
       25 . A method as claimed in  claim 24 , wherein the n×2n denotes 4×8, and 2n×2n denotes 8×8.