The document discusses camera calibration. It describes determining the internal optical parameters (IOP) of cameras like focal length and principal point coordinates. It discusses different distortion models like radial, decentric, and atmospheric distortions. It outlines laboratory, field, and stellar calibration methods. It explains how equivalent focal length, radial distortion, and calibrated focal length are calculated. It also mentions self-calibration, using calibration objects, and bundle adjustment methods for calibration.

1. Presented by:
Sandeep Sasidharan
IIT Kanpur

2.  Purpose of camera calibration
 Calibration distortion models
 Methods of calibration

3.  Determine the IOP of camera
 Focal length (f)
 The principal point co-ordinates (x0,y0)
 Image distortion parameters

4.  For carrying out photogrammetry
 Camera lens must provide perfect central projection
 Camera focal plane is perfectly flat
OR
 Camera lens perspective centre, the ground point
and the corresponding point on the image lies in a
straight line

5.  Radial lens distortion (RD)
 Decentric lens distortion (DLD)
 Atmospheric refraction distortion (ARD)
 Affine deformation distortion (ADD)

6.  Laboratory methods
 Field methods
 Stellar methods

7. Wolf, P.R.,(Elements of
photogrammetry)

8. Wolf, P.R.,(Elements of photogrammetry)

9.  Equivalent focal length
 FL at distortion free central area of lens
 EFL= (gf+ gh+ gs+ gt)/ 4 tan θ
 Radial lens distortion of each angle θ
 RD=EFL x tan n θ ( theoretically for angle n)
 Directly measured and averaged ( practical value)
 Difference of both gives RD for each angle

10.  Calibrated focal length
 FL which produces mean distribution of RD
 CFL is selected so that Max +ve RD = Max –ve RD
(D1-CFL tan θ1 + D2-CFL tan θ2 )=0
 Principal point location

11.  Target points are near to the centre and sparse
in outer areas and radial distortion is
predominant at outer areas
 Method is very expensive
 Measurements must be very accurate

12.  Self calibration
 Calibration using 2D/3D calibration objects
 Bundle Adjustment Method

13.  Development of new algorithms for IOP
determination
 Helped using less expensive digital cameras for
conventional photogrammetry