Apparatus and method for allocating bits temporaly between frames in a coding system

Abstract

A method and apparatus for temporally allocating bits between frames in a coding system such that temporal fluctuations are smoothed out. Namely, a picture quality is monitored on a frame by frame basis. An average distortion measure is derived from previous picture frames and that average is compared to the distortion measure of a current frame, where the result is used to effect bit budget allocation for each frame in an input image sequence.

1 . A method for adjusting a target bit rate for a frame, comprising: 
 (a) determining a picture quality measure of a current frame for a particular frame type;    (b) computing a difference between (i) an average picture quality measure of a plurality of immediately previous frames corresponding to said frame type of said current frame and (ii) the picture quality measure of said current frame for producing a resultant value; and    (c) adjusting said target bit rate based on the resultant value.    
   
   
       2 . The method of  claim 1 , wherein said frame type is an intra-frame.  
   
   
       3 . The method of  claim 1 , wherein said frame type is a predicted frame.  
   
   
       4 . The method of  claim 1 , wherein said frame type is a bi-directional predicted frame.  
   
   
       5 . The method of  claim 22 , where said adjusting step (c) comprises the step of: reducing said target bit rate if said resultant value is less than said threshold value.  
   
   
       6 . The method of  claim 22 , where said adjusting step (c) comprises the step of: increasing said target bit rate if said resultant value is greater than said threshold value.  
   
   
       7 . The method of  claim 1 , wherein said picture quality measure is a just noticeable difference (JND) measure.  
   
   
       8 . The method of  claim 1 , wherein said picture quality measure is a peak signal to noise ratio (PSNR) measure.  
   
   
       9 . The method of  claim 1 , wherein said picture quality measure is a mean square error (MSE) measure.  
   
   
       10 . The method of  claim 1 , wherein said plurality of immediately previous frames comprises said current frame.  
   
   
       11 . A computer readable medium having stored thereon a plurality of instructions including instructions which, when executed by a processor, causes the processor to perform a method comprising the steps of: 
 (a) determining a picture quality measure of a current frame for a particular frame type;    (b) computing a difference between (i) an average picture quality measure of a plurality of immediately previous frames corresponding to said frame type of said current frame and (ii) the picture quality measure of said current frame for producing a resultant value; and    (c) adjusting said target bit rate based on the resultant value.    
   
   
       12 . Apparatus for encoding an input image sequence having at least one input frame, where said frame is partitioned into at least one block, said apparatus comprising: 
 a block motion compensator for computing a motion vector for the block and for generating a predicted image using said motion vector;    a transform module for applying a transformation to a difference signal between the input frame and said predicted image, where said transformation produces a plurality of coefficients;    a quantizer for quantizing said plurality of coefficients with a quantizer scale;    a controller for adjusting a target bit rate for a current frame based on a difference of a picture quality measure of said current frame and an average picture quality measure of a plurality of immediately previous frames corresponding to a frame type of said current frame; and    a coder for coding said plurality of quantized coefficients.    
   
   
       13 . The apparatus of  claim 12 , wherein said frame type is an intra-frame.  
   
   
       14 . The apparatus of  claim 12 , wherein said frame type is a predicted frame.  
   
   
       15 . The apparatus of  claim 12 , wherein said frame type is a bi-directional predicted frame.  
   
   
       16 . The apparatus of  claim 12 , wherein said controller reduces said target bit rate if said resultant value is less than a threshold value.  
   
   
       17 . The apparatus of  claim 12 , wherein said controller increases said target bit rate if said resultant value is greater than a threshold value.  
   
   
       18 . The apparatus of  claim 12 , wherein said picture quality measure is a just noticeable difference (JND) measure.  
   
   
       19 . The apparatus of  claim 12 , wherein said picture quality measure is a peak signal to noise ratio (PSNR) measure.  
   
   
       20 . The apparatus of  claim 12 , wherein said picture quality measure is a mean square error (MSE) measure.  
   
   
       21 . The apparatus of  claim 13 , wherein said plurality of immediately previous frames measure comprises said current frame.  
   
   
       22 . The method of  claim 1 , further comprising comparing the resultant value to a threshold value for producing a comparing result.  
   
   
       23 . The method of  claim 1 , further comprising computing said average picture quality measure of said plurality of immediately previous frames from a picture quality measure for each of said plurality of immediate previous frames.  
   
   
       24 . The method of  claim 1 , further comprising determining each picture quality measures for each of said plurality of immediate previous frames.