ISPRS Commission III, Vol.34, Part 3A „Photogrammetric Computer Vision‘, Graz, 2002 
  
  
The analysis of record pixels positions with respect to 
resulting image 
The enhancement fulfilling the following is 
considered: 
R<S 2 (14) 
where 
S - the length of record pixel side 
R - the length of resulting image pixel side 
This conditions reduces the number of 
possible types of relative positions of record pixels 
with recpect to the resulting image to four types. Even 
for doubling of the resolution these equation is valid. 
The four types of actual pixel cover are possible: 
I" type: Actual pixel is covered by part of one record 
pixel. 
2"type: Actual pixel is covered by two parts of 
neighbouring record pixels. 
3" type: Actual pixel is covered by three parts of 
neighbousring record pixels. 
4" type: Actual pixel is covered by four parts of 
neighbousring record pixels. 
The examples of every type are illustrated in the 
Figure 7. 
  
Figure 7 Four possible types of resulting image pixel 
covering by record pixels 
The actual pixel type is determined by 
enumerating the number of record pixels overlapping 
It. 
It is done by investigation of relative positions of all 
pairs of neigbouring R and S-lines with respect to the 
actual pixel. It is not necessary to investigate all the 
pairs. With suitable order of investigated pixels in 
resulting image it is possible to reduce this number. 
The procedure in this method is as follows: 
The actual pixel vertices positions with respect to 
record R and S-lines are determined. From this 
information it is detected whether actual pixel is 
bounded by one, two or four pixels of the record. In 
case of one or two bounding pixels these pixels 
already overlap the actual pixel. However if this pixel 
is bounded by four record pixels it doesn‘t mean that 
all four pixels overlap it. There can occur the case 
with only three pixels overlaping it. The determination 
of these positions is done by determining the 
intersection of bounding record pixels position. If this 
intersection is in interior of investigated pixel the it is 
overlapped by four record pixels else it is overlaped 
by three. 
  
P - mtersection of record bounded pixel 
Figure 8 Two possibilities of actual pixel overlap in 
case of four bounding pixels 
The calculation of pixels parts overlaping the actual 
pixel 
Because It is already known how many pixels 
overlap actual pixel it is possible to determine the 
areas of parts of all overlapping pixels. 
Because the areas are polygons (with at most 
6 vertices) at first the coordinates of polygons vertices 
are calculated which are intersections of R and S-lines 
of the record and resulting image. The polygons are 
divided into triangles or trapuziums respectively. By 
enumeration of its areas and by addition the areas of 
the overlapping pixels parts are determined. 
For acceleration of the method and reduction 
of number of arithmetic operations first the pixles 
parts are sorted according to their vertices number. 
Then the areas of all pixles parts are calculated except 
the last one with greates number of vertices. The area 
of that pixel part is computed by subdividing all the 
previously computed parts areas from area of the 
whole pixel. Example is illustrated in Figure 9. S;, S,, 
$; are record pixel parts overlapping the actual pixel, 
S; is the are of triangle ABC, S; is the area of the 
triangle DEF, S; is calculed by S; = R° - S, - S, 
  
Figure 9 The computation of the pixel part S; 
The determination of actual pixel color 
On a basis of known areas of the overlapping 
pixels parts of the records it is possible to determine 
the amount of contributions of record pixels to the 
resulting color of actual pixel. 
The color which contributes to the resulting 
color of actual pixel willl be the weighted average of 
color of record pixels overlapping the actual pixel. 
The weights are areas of pixle parts covering the 
actual pixel. 
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