Methods and apparatus for dynamically adjusting f-codes for a digital picture header

Abstract

The present invention provides methods and apparatus for dynamically adjusting f-codes for a digital picture header of a coded picture. A video encoder having at least one motion estimation stages is provided for encoding the current picture. Motion vectors are determined for one motion estimation stage of the encoder. The motion vectors are analyzed to determine a maximum motion vector range for the picture. A corresponding minimum f-code is determined for the maximum range. The minimum f-code is then inserted into the digital picture header. In this manner, the f-codes carried in the digital picture header can be reduced to the minimum required value, thus reducing the number of bits needed to encode the f-codes.

1 . A method for dynamically adjusting f-codes for a digital picture header of a coded picture, comprising the steps of: 
 determining motion vectors for one motion estimation stage of a video encoder encoding said picture, said video encoder having at least two motion estimation stages;    analyzing the motion vectors to determine a maximum motion vector range for said picture;    determining a corresponding minimum f-code for said maximum range; and    inserting said minimum f-code into the digital picture header.    
   
   
       2 . A method in accordance with  claim 1 , wherein: 
 said motion vectors are determined for use during a second to last motion estimation stage; and    said minimum f-code is inserted into said digital picture header prior to encoding said picture.    
   
   
       3 . A method in accordance with  claim 1 , wherein: 
 said motion vectors are determined for use during a final motion estimation stage; and    the digital picture header containing said minimum f-code is constructed subsequent to said final motion estimation stage.    
   
   
       4 . A method in accordance with  claim 1 , wherein: 
 said maximum range comprises at least one of a maximum horizontal range or a maximum vertical range; and    a corresponding minimum vertical f-code and a minimum horizontal f-code is determined for each of said maximum ranges.    
   
   
       5 . A method in accordance with  claim 4 , wherein: 
 said maximum horizontal and maximum vertical ranges may be ranges of either a field or a frame of said picture.    
   
   
       6 . (canceled)  
   
   
       7 . (canceled)  
   
   
       8 . (canceled)  
   
   
       9 . (canceled)  
   
   
       10 . A method in accordance with  claim 1 , wherein: 
 said encoding comprises two-pass encoding; and    motion vectors from a first pass encoding are used to determine the f-codes needed for a second pass encoding.    
   
   
       11 . A method in accordance with  claim 10 , further comprising: 
 determining during said second pass encoding whether any motion vectors exceed the f-code range established by the f-codes from said first pass encoding; and    reducing the values of any such motion vectors which exceed the f-code range.    
   
   
       12 . A method in accordance with  claim 1 , wherein: 
 said picture is a B-picture; and    separate minimum f-codes are determined for forward motion vectors and for backward motion vectors.    
   
   
       13 . A method in accordance with  claim 1 , wherein: 
 said encoding comprises high definition television encoding.    
   
   
       14 . A method in accordance with  claim 1 , wherein said picture comprises an MPEG-2 picture.  
   
   
       15 . Encoder apparatus for dynamically adjusting f-codes for a digital picture header of a coded picture, comprising: 
 at least one motion estimation stage for determining motion vectors for use in encoding said picture;    a motion vector selector capable of analyzing motion vectors from one of the motion estimation stages to determine a maximum motion vector range for said picture; and    an f-code processor capable of determining a corresponding minimum f-code for said maximum range;    wherein said minimum f-code is inserted into the digital picture header.    
   
   
       16 . Apparatus in accordance with  claim 15 , wherein: 
 said motion vectors are determined for use during a second to last motion estimation stage; and    said minimum f-code is inserted into said digital picture header prior to encoding said picture.    
   
   
       17 . Apparatus in accordance with  claim 15 , wherein: 
 said motion vectors are determined for use during a final motion estimation stage; and    the picture header containing said minimum f-code is constructed subsequent to said final motion estimation stage.    
   
   
       18 . Apparatus in accordance with  claim 15 , wherein: 
 said maximum range comprises at least one of a maximum horizontal range or a maximum vertical range; and    said f-code processor determines a corresponding minimum vertical f-code and a minimum horizontal f-code for each of said maximum ranges.    
   
   
       19 . Apparatus in accordance with  claim 18 , wherein: 
 said maximum horizontal and maximum vertical ranges may be ranges of either a field or a frame of said picture.    
   
   
       20 . (canceled)  
   
   
       21 . (canceled)  
   
   
       22 . (canceled)  
   
   
       23 . (canceled)  
   
   
       24 . Apparatus in accordance with  claim 15 , comprising: 
 a first pass encoder; and    a second pass encoder;    wherein motion vectors from a first pass encoding are used to determine the f-codes needed for a second pass encoding.    
   
   
       25 . Apparatus in accordance with  claim 24 , further comprising: 
 a vector processor capable of: 
 determining whether any motion vectors exceed the f-code range established by the f-codes from said first pass encoder; and  
 reducing the values of any such motion vectors which exceed the f-code range.  
   
   
   
       26 . Apparatus in accordance with  claim 15 , wherein: 
 said picture is a B-picture; and    separate minimum f-codes are determined for forward motion vectors and for backward motion vectors.    
   
   
       27 . Apparatus in accordance with  claim 15 , wherein: 
 said encoding comprises high definition television encoding.    
   
   
       28 . Apparatus in accordance with  claim 15 , wherein said picture comprises an MPEG-2 picture.