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OBJECT BASED DETERMINATION OF COMPARATOR COORDINATES 
IN BLURRED IMAGES 
by Alfons Meid, Aarau (Switzerland); Development Engineer at Leica Heerbrugg AG; 
ISPRS Washington 1992 , Commission V 
Abstract : 
A method for the determination of 2D comparator coordinates in blurred images for orientation and photogram- 
metric point determination purposes is described. From a certain amount of image blur it provides an accuracy en- 
hancement compared to visual or edge based digital measurement. Homologous image points are defined based on 
geometric optical laws. The method is applied to images blurred by an inproper arrangement of the optical compo- 
nents between object and image surface; it may be extended to images blurred by any physical reason. The results 
obtained by processing a 3D-point determination for a multi-media image block prove the practicability of this 
method. 
KEY WORDS : Comparator Coordinates, Blurred Images, Ray Tracing, Target Matching, Bundle Adjustment 
1.0ccurance of Blurred Images 
A blurred image is the result of disturbed optical 
imaging and can be caused by several physical ef- 
fects: 
- bw relative movement between camera and ob- 
ject; this is mainly a problem of aerial photo- 
grammetry 
- by a reduced resolution of the image sensor; this 
can be noticed very well on colour sensitive CCD 
cameras 
- by an inproper arrangement of the optical com- 
ponents. 
- A by many other reasons, e.g. specific characteris- 
tics of films emulsions, film processing or light 
scattering between object and camera (see Kup- 
fer 1972 and Mertens 1980). 
This paper deals with the case of inproperly arranged 
optical components, which means, that the relative 
spatial positions of camera and object are not well ad- 
justed to the refraction properties of the media be- 
tween image plane and object . This leads to: 
1. Unsharpness, caused by geometric optical aberra- 
tions of rays. 
2. Variations of the distortion within the small image 
of the point target. In the context of this paper distor- 
tion means any shift of an image point within the 
image plane from the position resulting from a pure 
central perspective transformation to another posi- 
tion by any physical reason. 
3. Unsharpness, caused by diffraction. 
This paper deals with unsharpness as stated in point 
1. and distortion variations, as stated in point 2. Only 
these two effects are called aberrations in this con- 
text. Note this definition of "aberrations" differs from 
that used in optical science, where not only distortion 
variations, but distortions themselves are defined as 
aberrations, too. But these do not affect the measure- 
ment of comparator coordinates. See Fig. 1 as an ex- 
ample for geometric optical aberrations: the target on 
the left side is imaged to a blurred target image, to be 
seen on the rigth side. 
The diffraction, named under 3. is not included for 
reasons described later in section 2.2. 
The problem of inproper arranged optical components 
is typical for a wide range of close range applications. 
For example: 
- A certain depth of field, required due to network op- 
timization, can overtax the optical capabilities of the 
used camera. 
- In the extreme close range there is no depth of field; 
unsharp images can only be avoided if the object is 
completely flat and the camera fulfills the 
Scheimpflug-condition. 
- In multi-media applications further optical compo- 
nents, i.e. refracting surfaces and refraction indices of 
media, are added to the space between object and 
camera (Fig. 2). In general, this leads to reduced 
image quality, because the blur minimization of a 
standard lens design is valid only if one specific me- 
dium is located between lens and object.