Picture encoding method, picture encoding apparatus and picture recording medium

Abstract

This invention employs a scheme to allow an input video signal to undergo encoding, e.g., predictive encoding, DCT processing, quantization at fixed quantization step size and variable length encoding to generate first encoded data to determine (calculate) allocated code quantity every frame or every GOP on the basis of data quantity every predetermined time, e.g., every frame or every GOP of the first encoded data and total quantity of usable data to encode the input video signal every predetermined time on the basis of the allocated code quantity to generate second encoded data. Thus, variable rate encoding such that encoding rate changes every predetermined time is realized. As a result, even if pictures (frames) of complicated are successive, there is no possibility that quantization step size is caused to be large with respect to these pictures as in the conventional apparatus. Thus, uniform high picture quality can be obtained through the entirety. Further, since second encoded data obtained in a manner as described above has variable rate, in the case where such encoded data is recorded onto picture recording media, limited memory capacity can be effectively used, and recording time of picture recording media can be prolonged. In addition, picture data of high picture quality uniform over the entirety can be reproduced from the picture recording media.

1. An encoding method, comprising the steps of:
 receiving an input video signal;  
 selectively encoding at least a portion of said input video signal by intra-frame encoding or predictive encoding to generate first encoded data, said predictive encoding including forward predictive encoding and backward predictive encoding;  
 transform encoding said first encoded data to generate first coefficient data;  
 quantizing said first coefficient data by a fixed step size;  
 variable length encoding said first quantized data to generate a first bit stream;  
 determining an encoding rate of said first bit stream every GOP as a function of a data quantity of intra-frame and forward-predictive encoded pictures only in the GOP;  
 selectively encoding said input video signal by intra-frame or predictive encoding to generate second encoded data;  
 transform encoding said second encoded data to generate second coefficient data;  
 setting a variable step size according to the encoding rate determined every GOP;  
 quantizing said second coefficient data by said variable step size;  
 variable length encoding said second quantized data to generate a second bit stream; and  
 outputting said second bit stream.  
 
     
     
       2. An encoding apparatus, comprising:
 means for receiving an input video signal;  
 means for selectively encoding at least a portion of said input video signal by intra-frame encoding or predictive encoding to generate first encoded data, said predictive encoding including forward predictive encoding and backward predictive encoding;  
 means for transform encoding said first encoded data to generate first coefficient data;  
 means for quantizing said first coefficient data by a fixed step size;  
 means for variable length encoding said first quantized data to generate a first bit stream;  
 means for determining an encoding rate of said first bit stream every GOP as a function of a data quantity of intra-frame and forward-predictive encoded pictures only in the GOP;  
 means for selectively encoding said input video signal by intra-frame or predictive encoding to generate second encoded data;  
 means for transform encoding said second encoded data to generate second coefficient data;  
 means for setting a variable step size according to the encoding rate determined every GOP;  
 means for quantizing said second coefficient data by said variable step size;  
 means for variable length encoding said second quantized data to generate a second bit stream; and  
 means for outputting said second bit stream.  
 
     
     
       3. A recording medium on which there is recorded a second bit stream obtained by:
 receiving an input video signal;  
 selectively encoding at least a portion of said input video signal by intra-frame encoding or predictive encoding to generate first encoded data, said predictive encoding including forward predictive encoding and backward predictive encoding;  
 transform encoding said first encoded data to generate first coefficient data;  
 quantizing said first coefficient data by a fixed step size;  
 variable length encoding said first quantized data to generate a first bit stream;  
 determining an encoding rate of said first bit stream every GOP as a function of a data quantity of intra-frame and forward-predictive encoded pictures only in the GOP;  
 selectively encoding said input video signal by intra-frame or predictive encoding to generate second encoded data;  
 transform encoding said second encoded data to generate second coefficient data;  
 setting a variable step size according to the encoded data rate determined every GOP;  
 quantizing said second coefficient data by said variable step size;  
 variable length encoding said second quantized data to generate a second bit stream; and  
 recording said second bit stream on said recording medium.  
 
     
     
       4. An encoding method, comprising the steps of:
 receiving an input video signal;  
 selectively encoding at least a portion of said input video signal by inter-frame encoding or predictive encoding to generate first encoded data, said predictive encoding including forward predictive encoding and backward predictive encoding;  
 transform encoding said first encoded data to generate first coefficient data;  
 quantizing said first coefficient data by a fixed step size;  
 variable length encoding said first quantized data to generate a first bit stream;  
 determining a difficulty of encoding said first bit stream every GOP based on inter-frame and forward-predictive encoded pictures only in the GOP;  
 calculating an encoding rate frame said difficulty of encoding determined every GOP;  
 selectively encoding said input video signal by intra-frame or predictive encoding to generate second encoded data;  
 transform encoding said second encoded data to generate second coefficient data;  
 quantizing the second coefficient data by a step size set according to said calculated encoding rate;  
 variable length encoding said second quantized data to generate a second bit stream; and  
 outputting said second bit stream.  
 
     
     
       5. An encoding apparatus, comprising:
 means for receiving an input video signal;  
 means for selectively encoding at least a portion of said input video signal by intra-frame encoding or predictive encoding to generate first encoded data, said predictive encoding including forward predictive encoding and backward predictive encoding;  
 means for transform encoding said first encoded data to generate first coefficient data;  
 means for quantizing said first coefficient data by a fixed step size;  
 means for variable length encoding said first quantized data to generate a first bit stream;  
 means for determining a difficulty of encoding said first bit stream every GOP based on intra-frame and forward-predictive encoded pictures only in the GOP;  
 means for calculating an encoding rate from said difficulty of encoding determined every GOP;  
 means for selectively encoding said input video signal by intra-frame or predictive encoding to generate second encoded data;  
 means for transform encoding said second encoded data to generate second coefficient data;  
 means for quantizing the second coefficient data by a step size set according to said calculated encoding rate;  
 means for variable length encoding said second quantized data to generate a second bit stream; and  
 means for outputting said second bit stream.  
 
     
     
       6. A recording medium on which there is recorded a second bit stream obtained by:
 receiving an input video signal;  
 selectively encoding at least a portion of said input video signal by intra-frame encoding or predictive encoding to generate first encoded data, said predictive encoding including forward predictive encoding and backward predictive encoding;  
 transform encoding said first encoded data to generate first coefficient data;  
 quantizing said first coefficient data by a fixed step size;  
 variable length encoding said first quantized data to generate a first bit stream;  
 determining a difficulty of encoding said first bit stream every GOP based on intra-frame and forward-predictive encoded pictures only in the GOP;  
 calculating an encoding rate from said difficulty of encoding determined every GOP;  
 selectively encoding said input video signal by intra-frame or predictive encoding to generate second encoded data;  
 transform encoding said second encoded data to generate second coefficient data;  
 quantizing the second coefficient data by a step size set according to said calculated encoding rate;  
 variable length encoding said second quantized data to generate a second bit stream; and  
 recording said second bit stream on said recording medium.  
 
     
     
       7. An encoding method, comprising the steps of:
 receiving an input video signal;  
 selectively encoding at least a portion of said input video signal by intra-frame or predictive encoding to generate first encoded data representing intra-frame or predictive encoded pictures, respectively;  
 transform encoding said first encoded data to generate first coefficient data;  
 quantizing said first coefficient data by a fixed step size;  
 variable length encoding said first quantized data to generate a first bit stream;  
 counting a data quantity of said first bit stream every predetermined time to indicate a difficulty of encoding;  
 determining said difficulty of encoding said first bit stream based on intra-frame and forward-predictive encoded pictures only;  
 calculating an allocated code quantity for each unit of predetermined time as a function of said difficulty of encoding so that said allocated code quantity is set to be larger for complex pictures and smaller for simple pictures;  
 selectively encoding said input video signal by intra-frame or predictive encoding to generate second encoded data;  
 transform encoding said second encoded data to generate second coefficient data;  
 quantizing said second coefficient data at a step size set in response to said allocated code quantity;  
 variable length encoding said second quantized data to generate a second bit stream; and  
 outputting said second bit stream.  
 
     
     
       8. A method according to  claim 7 , wherein the fixed quantization step size equals one. 
     
     
       9. A method according to  claim 7 , further comprising the step of storing said second bit stream in a buffer before it is output, wherein said quantization step size is further based on a quantity of said second bit stream stored in said buffer. 
     
     
       10. A method according to  claim 7 , wherein said predetermined time is a frame. 
     
     
       11. An encoding apparatus, comprising:
 means for receiving an input video signal;  
 means for selectively encoding at least a portion of said input video signal by intra-frame or predictive encoding to generate first encoded data representing intra-frame or predictive encoded pictures, respectively;  
 means for transform encoding said first encoded data to generate first coefficient data;  
 means for quantizing said first coefficient data by a fixed step size;  
 means for variable length encoding said first quantized data to generate a first bit stream;  
 means for counting a data quantity of said first bit stream every predetermined time to indicate a difficulty of encoding;  
 means for determining said difficulty of encoding said first bit stream based on intra-frame and forward-predictive encoded pictures only;  
 means for calculating an allocated code quantity for each unit of predetermined time as a function of said difficulty of encoding so that said allocated code quantity is set to be larger for complicated pictures and smaller for simple pictures;  
 means for selectively encoding said input video signal by intra-frame or predictive encoding to generate second encoded data;  
 means for transform encoding said second encoded data to generate second coefficient data;  
 means for quantizing said second coefficient data at a step size set in response to said allocated code quantity;  
 means for variable length encoding said second quantized data to generate a second bit stream; and  
 means for outputting said second bit stream.  
 
     
     
       12. An apparatus according to  claim 11 , wherein the fixed quantization step size equals one. 
     
     
       13. An apparatus according to  claim 11 , further comprising a buffer for storing said second bit stream before it is output, wherein said quantization step size is further based on a quantity of said second bit stream stored in said buffer. 
     
     
       14. An apparatus according to  claim 11 , wherein said predetermined time is a frame. 
     
     
       15. A recording medium on which there is recorded a second bit stream obtained by:
 receiving an input video signal;  
 selectively encoding at least a portion of said input video signal by intra-frame or predictive encoding to generate first encoded data representing intra-frame or predictive encoded pictures, respectively;  
 transform encoding said first encoded data to generate first coefficient data;  
 quantizing said first coefficient data by a fixed step size;  
 variable length encoding said first quantized data to generate a first bit stream;  
 counting a data quantity of said first bit stream every predetermined time to indicate a difficulty of encoding;  
 determining said difficulty of encoding said first bit stream based on intra-frame and forward-predictive encoded pictures only;  
 calculating an allocated code quantity for each unit of predetermined time as a function of said difficulty of encoding so that said allocated code quantity is set to be larger for complicated pictures and smaller for simple pictures;  
 selectively encoding said input video signal by intra-frame or predictive encoding to generate second encoded data;  
 transform encoding said second encoded data to generate second coefficient data;  
 quantizing said second coefficient data at a step size set in response to said allocated code quantity;  
 variable length encoding said second quantized data to generate a second bit stream; and  
 recording said second bit stream on said recording medium.  
 
     
     
       16. An encoding method for encoding source video data, the method comprises the steps of:
   encoding said source video data with a predetermined quantization step size to generate first encoded data;        detecting a difficulty of the encoding process of source video data based on bit amount of said first encoded data;        deciding an optimum quantization step size, said optimum quantization step size being varied depending on said difficulty so that said optimum quantization step size becomes smaller when said source video data is more complex and said optimum quantization step size becomes larger when source video data to be encoded is more simple; and        encoding said source video data by using said optimum quantization step on encoding unit basis,        wherein the predetermined quantization step size has a fixed value and the optimum quantization step size has a non - fixed value,        wherein said source video data is always encoded using said predetermined quantization step and said optimum quantization step in which the predetermined quantization step size is always different from the optimum quantization step size.      
     
     
       17. An encoding method for encoding source video data, the method comprises the steps of:
   encoding said source video data with a predetermined quantization step size to generate first encoded data;        detecting a difficulty of the encoding process of source video data based on bit amount of said first encoded data;        calculating an allocated code quantity which is varied depending on said difficulty so that said allocated code quantity is more increased when said source video data is more complex and said allocated code quantity is more decreased when source video data is more simple; and        encoding said source video data by an optimum quantization step size based on said allocated code quantity,        wherein the optimum quantization step size has a non - fixed value, and        wherein said source video data is always encoded using said predetermined quantization step and said optimum quantization step in which the predetermined quantization step size is always different from the optimum quantization step size.      
     
     
       18. An encoding method for encoding source video data, the method comprises the steps of:
   detecting motion vector of a macro block of said source video data;        encoding said macro block of said source video data by using a predetermined quantization step size and said detected motion vector to generate first encoded data;        detecting a difficulty of the encoding process of source video data based on amount of said first encoded data;        deciding an optimum quantization step size, said optimum quantization step size being varied depending on said difficulty so that said optimum quantization step size becomes smaller when said source video data is more complex and said optimum quantization step size becomes larger when source video data be encoded is more simple; and        encoding said macro block of said source video data by using said optimum quantization step and said detected motion vector,        wherein the predetermined quantization step size has a fixed value and the optimum quantization step size has a non-   fixed value, and        wherein said source video data is always encoded using said predetermined quantization step and said optimum quantization step in which the predetermined quantization step size is always different from the optimum quantization step size.      
     
     
       19. An encoding method for encoding source video data, the method comprises the steps of:
   selecting a predictive mode of a macro block of said source video data;        encoding said macro block of said source video data by using a predetermined quantization step size and said selected predictive mode to generate first encoded data;        detecting a difficulty of the encoding process of source video data based on amount of said first encoded data;        deciding an optimum quantization step size, said optimum quantization step size being varied depending on said difficulty so that said optimum quantization step size becomes smaller when said source video data is more complex and said optimum quantization step size becomes larger when source video data to be encoded is more simple; and        encoding said macro block of said source video data by using sad optimum quantization step and said selected predictive mode,        wherein the predetermined quantization step size has a fixed value and the optimum quantization step size has a non - fixed value, and        wherein said source video data is always encoded using said predetermined quantization step and said optimum quantization step in which the predetermined quantization step size is always different from the optimum quantization step size.      
     
     
       20. An encoding apparatus for encoding source video data, the apparatus comprising:
   means for detecting motion vector of a macro block of said source video data;        first encoding means for encoding said macro block of said source video data by using a predetermined quantization step size and said detected motion vector to generate first encoded data;        means for detecting a difficulty of the encoding process of source video data based on amount of said first encoded data;        means for deciding an optimum quantization step size, said optimum quantization step size being varied depending on said difficulty so that said optimum quantization step size becomes smaller when said source video data is more complex and said optimum quantization step size becomes larger when source video data to be encoded is more simple; and        second encoding means for encoding said macro block of said source video data by using said optimum quantization step and said detected motion vector,        wherein the predetermined quantization step size has a fixed value and the optimum quantization step size has a non - fixed value, and        wherein said source video data is always encoded using said predetermined quantization step and said optimum quantization step in which the predetermined quantization step size is always different from the optimum quantization step size.      
     
     
       21. An encoding apparatus for encoding source video data, the apparatus comprising:
   means for selecting a predictive mode of a macro block of said source video data;        first encoding means for encoding said macro block of said source video data by using a predetermined quantization step size and said selected predictive mode to generate first encoded data;        means for detecting a difficulty of the encoding process of source video data based on amount of said first encoded data;        means for deciding an optimum quantization step size, said optimum quantization step size being varied depending on said difficulty so that said optimum quantization step size becomes smaller when said source video data is more complex and said optimum quantization step size becomes larger when source video data to be encoded is more simple; and        second encoding means for encoding said macro block of said source video data by using said optimum quantization step and said selected predictive mode,        wherein the predetermined quantization step size has a fixed value and the optimum quantization step size has a non - fixed value, and        wherein said source video data is always encoded using said predetermined quantization step and said optimum quantization step in which the predetermined quantization step size is always different from the optimum quantization step size.      
     
     
       22. An encoding apparatus for encoding source video data, the apparatus comprising:
   first encoding means for encoding said source video data with a predetermined quantization step size to generate first encoded data;        second encoding means for encoding said source video data based on supplied quantization step size to generate second encoded data;        transmitting buffer for buffering said second encoded data; and        control means for detecting a difficulty of the encoding process in said first encoding means, and for deciding said quantization step size, said optimum quantization step size being varied depending on said difficulty so that said quantization step size becomes smaller when said source video data is more complex and said quantization step size becomes larger when source video data to be encoded is more simple, and said quantization step size being dependent on a remaining capacity of said transmitting buffer so as to suppress overflow and underflow in said transmitting buffer,        wherein the predetermined quantization step size has a fixed value and the optimum quantization step size has a non - fixed value, and        wherein said source video data is always encoded using said predetermined quantization step and said optimum quantization step in which the predetermined quantization step size is always different from the optimum quantization step size.