Method for calibrating a camera

Abstract

A method calibrates a camera having image sensor having a center position. An image view projected onto the image sensor by a lens is captured. At least one image view boundary of the captured image view is detected. A projection center position corresponding to a center of the projected image view is determined in at least one dimension. Offset between the projection center position and a sensor center position is determined, defined in at least one dimension, corresponding to the center of the image sensor capturing the projected image view. The image sensor is moved in relation to the lens based on the offset in order to arrive at a substantially zero offset in at least one dimension between the center of image sensor and the center of the projected image view.

What is claimed is: 
     
         1 . A method for calibrating a camera including an image sensor having a center position, the method comprising:
 capturing an image view projected onto the image sensor by a lens, the projected image view having a center,   detecting at least one image view boundary of the image view captured by the image sensor,   determining, in at least one dimension, a projection center position corresponding to the center of the projected image view on the image sensor based on detected boundary,   determining offset between the projection center position and the sensor center position, defined in at least one dimension, corresponding to the center of the image sensor capturing the projected image view, and   moving the image sensor in relation to the lens based on the offset in order to arrive at a substantially zero offset in at least one dimension between the center of image sensor and the center of the projected image view.   
     
     
         2 . The method according to  claim 1 , further comprising:
 performing an additional capture of the image view projected onto the image sensor at a point in time after the moving of the sensor,   detecting at least one image view boundary relating to the latter captured image view projected onto the image sensor,   determining, in at least one dimension, an updated projection center position corresponding to the center of the projected image view on the image sensor based on latter detected boundary,   determining offset between the updated projection center position and the sensor center position, defined in at least one dimension, corresponding to the center of the image sensor capturing the projected image view, and   if the offset is not zero or not substantially zero then moving the image sensor in relation to the lens based on the offset in order to arrive at a substantially zero offset in at least one dimension between the center of image sensor and the center of the projected image view.   
     
     
         3 . The method according to  claim 1 , wherein the image view is projected onto the image sensor through a wide angle lens which is producing a circular image or at least a substantially circular image. 
     
     
         4 . The method according to  claim 3 , wherein the determining the position of the center of the projected image view includes calculating parameters defining a circle that are likely to represent the at least one detected edge relating to the projected image view. 
     
     
         5 . The method according to  claim 4 , wherein calculating parameters defining a circle that are likely to represent the at least one detected edge relating to the projected image view is based on a Hough transform. 
     
     
         6 . The method according to  claim 1 , wherein the camera comprises a pan and tilt enabled camera head including the image sensor, wherein the image view is projected onto the image sensor through a lens fixedly arranged in relation to a base of the camera, and wherein the moving of the image sensor includes moving of the camera head in relation to the fixedly arranged lens. 
     
     
         7 . The method according to  claim 6 , wherein the moving of the camera head is performed as pan and/or tilt movements calculated from the offset between the center of projected image view and center of the image sensor capturing the projected image view. 
     
     
         8 . The method according to  claim 6 , further comprising saving a tilt angle of the camera head in response to the offset between the projection center position and the sensor center position being determined to be zero or substantially zero. 
     
     
         9 . A method for calibrating a camera comprising:
 a) selecting a position in an overview image view captured by the camera and presented to the operator,   b) calculating a pan angle and a tilt angle corresponding to the selected position,   c) moving the camera head to a position in which it may capture a detailed image view, not through the wide angle lens, having a center representing the calculated pan angle and tilt angle,   d) adjusting the camera head, after the camera head has moved to the position, until the position selected in the overview image is centered in the detailed view,   e) saving data representing the amount of adjustment used in for centering the position in detailed view,   repeating the steps (a-e) until a predetermined amount of data relating to the adjustment has been saved, and   estimating an error-function based on the saved data.   
     
     
         10 . The method according to  claim 9 , wherein the act of estimating an error function includes determining coefficients of a polynomial error function using Linear Least Square Estimation. 
     
     
         11 . A method for transforming a selected position in an overview image captured by a camera to a pan and tilt angle for a camera that are to capture a more detailed view of the selected position, the method comprising:
 calculating the pan and tilt angle for the selected position based on the selected position in the overview image, and   compensating the resulting pan tilt angle based on an error function achieved by means of the following process:   a) selecting a position in an overview image view captured by the camera and presented to the operator,   b) calculating a pan angle and a tilt angle corresponding to the selected position,   c) moving the camera head to a position in which it may capture a detailed image view, not through the wide angle lens, having a center representing the calculated pan angle and tilt angle,   d) adjusting the camera head, after the camera head has moved to the position, until the position selected in the overview image is centered in the detailed view,   e) saving data representing the amount of adjustment used in for centering the position in detailed view,   repeating the steps (a-e) until a predetermined amount of data relating to the adjustment has been saved, and   estimating an error function based on the saved data.