Vertical compensation in a moving camera

Abstract

A hand-held device comprising a housing ( 10 ) shaped and dimensioned to allow the device to be hand held, a display ( 12 ) secured to the housing for displaying moving pictures on a frame-by-frame basis, and a camera ( 16, 18 ) having an optical axis (O) extending generally away from the display to image a person who is viewing the display. The hand-held device further comprises a sensor ( 20 ) configured to determine a rotational angle between an alignment axis (V) of the hand-held device and a reference alignment axis in real space. Alternative embodiments use a reference alignment axis obtained on the basis of data content of the images, as determined by image processing techniques. In this way, subjective picture quality can be improved by compensating for vertical mis-alignment of the image content of the frames obtained by the camera.

What is claimed is:  
     
         1 . A device comprising: 
 (a) a housing shaped and dimensioned to allow the device to be hand held;    (b) a display secured to the housing for displaying moving pictures on a frame-by-frame basis;    (c) a camera arranged in the housing so as to define an optical axis extending away from the housing in a direction from which the display is viewable, thereby to image an object positioned to view the display, the camera including a detector comprising an array of light sensitive elements for obtaining respective pixels of an image frame;    (d) a sensor operable to make measurements of a physical parameter from which a rotational angle between an alignment axis of the hand-held device and a reference alignment axis in real space can be determined; and    (e) a signal processing circuit arranged to associate image frames taken by the camera with respective rotational angles determined from the sensor measurements.    
     
     
         2 . A device according to  claim 1 , further comprising: 
 (f) an output stage arranged to output image frames taken by the camera; and    (g) a digital signal processor operatively arranged between the camera's detector and the output stage so as to apply a transform to each image frame taken by the camera prior to supply to the output stage, the transform being a rotation of the image frame through an angle derived from the rotational angle associated with that frame.    
     
     
         3 . A device according to  claim 2 , further comprising: 
 (h) a first frame memory connected in relation to the camera's detector to store at least one image frame from the camera's detector prior to frame transformation by the digital signal processor.    
     
     
         4 . A device according to  claim 3 , further comprising: 
 (i) a second frame memory connected in relation to the digital signal processor and the output stage to store at least one image frame after transformation by the digital signal processor.    
     
     
         5 . A device according to  claim 2 , wherein the output stage includes a wireless transmitter.  
     
     
         6 . A device according to  claim 2 , wherein the output stage includes an electrical or optical communication line for output of the image frames to a data carrier to allow storage of a sequence of image frames.  
     
     
         7 . A device according to  claim 6 , further comprising a drive for removably receiving a data carrier which, when loaded in the drive, is in operative communication with the electrical or optical communication line to allow storage of a sequence of image frames.  
     
     
         8 . A device according to  claim 1 , further comprising: 
 (f) an input stage for receiving image frames together with associated rotational angles; and    (g) a digital signal processor operatively arranged between the input stage and the display so as to apply a transform to each image frame received by the input stage prior to supply to the display, the transform being a rotation of the image frame through an angle derived from the rotational angle associated with that frame.    
     
     
         9 . A device according to  claim 8 , further comprising: 
 (h) a first frame memory connected in relation to the input stage to store at least one image frame from the input stage prior to frame transformation by the digital signal processors.    
     
     
         10 . A device according to  claim 9 , further comprising: 
 (i) a second frame memory connected in relation to the digital signal processor and the display to store at least one image frame after transformation by the digital signal processor.    
     
     
         11 . A device according to  claim 8 , wherein the input stage includes a wireless receiver.  
     
     
         12 . A device according to  claim 8 , further comprising a drive for removably receiving a data carrier which, when loaded in the drive, is in operative communication with the signal processing circuit to allow storage of a sequence of image frames together with associated rotational angles.  
     
     
         13 . A device according to  claim 1 , further comprising: 
 (f) a wireless transmitter arranged to output image frames taken by the camera together with associated rotational angles; and    (g) a wireless receiver arranged to receive image frames for loading onto the display.    
     
     
         14 . A device according to  claim 13 , wherein the wireless receiver is arranged so as to supply image frames to the display without rotational transformation.  
     
     
         15 . A device according to  claim 13 , further comprising: 
 a base station for wireless communication including 
 a receiver for receiving sequences of image frames with associated rotational angles;  
 a digital signal processor arranged to apply a transform to each image frame received with an associated rotational angle, the transform being a rotation of the image frame through an angle derived from the rotational angle associated with that frame; and  
 a transmitter for outputting a sequence of image frames transformed by the digital signal processor.  
   
     
     
         16 . An image processing method, comprising: 
 receiving a sequence of image frames taken by a camera;    determining a vertical alignment axis for each frame of the sequence;    applying a rotational transform to each frame through an angle determined from mis-alignment between a vertical alignment axis related to image content and a fixed alignment axis of the frame; and    outputting the sequence of image frames thus transformed to compensate for vertical misalignment of the image content of the frames.    
     
     
         17 . A method according to  claim 16 , wherein the angle is determined responsive to reference data of actual camera alignment in real space obtained contemporaneously with the frame concerned.