Image processing method and system

Abstract

In an image processing method a sequence of at least two image frames is provided and a motion vector representing relative movement of at least a part of said image frames is calculated. At least said part in the image frames is repositioned in accordance with the calculated motion vector, and the image frames are combined to form a combined image frame. The image frames are divided into blocks and a block motion vector representing relative movement of each block is calculated. Each block is repositioned in accordance with the calculated block motion vector and the blocks are combined to form combined blocks in order to obtain the combined image frame.

1 . Image processing method, comprising
 providing a sequence of at least two image frames   calculating a motion vector representing relative movement of at least a part of said image frames,   repositioning at least said part in the image frames in accordance with the calculated motion vector,   combining the image frames to form a combined image frame,   dividing the image frames into blocks,   calculating a block motion vector representing relative movement of each block,   repositioning each block in accordance with the calculated block motion vector and   combining the blocks to form combined blocks in order to obtain the combined image frame.   
   
   
       2 . Method according to  claim 1 , wherein the size of the blocks is determined according to the amount of the variation in the image frames. 
   
   
       3 . Method according to  claim 2 , wherein the amount of variation is determined by determining the deviation from the mean of a global motion vector, wherein the size of the blocks is reduced with respect to an initial size if the amount of variation exceeds a threshold value. 
   
   
       4 . Method according to  claim 2 , wherein the image frames are divided into blocks of an initial size, wherein the block motion vector is determined for at least a plurality of blocks of the initial size and the difference between the block motion vectors is used as a representation of the amount of variation, wherein the image frames are divided into blocks of a reduced size if the amount of variation exceeds a threshold value. 
   
   
       5 . Method according to  claim 2 , wherein the pixel values of corresponding blocks of the sequence of image frames are compared to determine the amount of variation, wherein the image frames are divided into blocks of a reduced size if the amount of variation exceeds a threshold value. 
   
   
       6 . Method according to  claim 2 , wherein a global motion vector is determined for the image frames, wherein a block motion vector for each of the blocks is determined by means of the global motion vector and the position of the block in the image frames. 
   
   
       7 . Method according to  claim 2 , wherein pixel values in the boundary areas of the repositioned blocks are checked for mismatch, wherein if the mismatch between the pixel values exceeds a threshold value the size of the blocks is reduced and the steps to obtain the combined image frame are repeated. 
   
   
       8 . Method according to  claim 2 , wherein the pixel values in the boundary areas of the repositioned blocks are averaged. 
   
   
       9 . Method according to  claim 8 , wherein the pixel values in the boundary areas of the repositioned blocks are averaged according to a weighting algorithm. 
   
   
       10 . Method according to  claim 2 , wherein a high resolution image is used as a first image, wherein the blocks of each further image are repositioned with respect to the blocks of the high resolution image. 
   
   
       11 . Image processing system for forming a combined image frame from a plurality of image frames, which the image processing system comprises an arrangement for loading an array of pixel values of a first image and at least an array of pixel values of one further image, the image processing system being configured to perform the steps of
 calculating a motion vector representing relative movement of at least a part of said image frames,   repositioning at least said part in the image frames in accordance with the calculated motion vector,   combining the image frames to form a combined image frame, wherein said system is further configured   to divide the image frames into blocks,   to calculate a block motion vector representing relative movement of each block,   to reposition each block in accordance with the calculated block motion vector and   to combine the blocks to form combined blocks in order to obtain the combined image frame.   
   
   
       12 . Computer program configured, when loaded into a programmable processing device ( 1 ) to enable the programmable processing device to carry out a method according to  claim 1 . 
   
   
       13 . Digital camera comprising an image processing system according to  claim 11 .