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4.6 Image Correction
2400 2600 2800 3000 3200 3400 3600 3800 4000 4200
0
0.2
0.4
0.6
0.8
1
Histogram of the uncorrected grey reference image
Grey level, 12 Bit [DN]
Relative number of pixels [−]
grey reference image ok
grey reference image too bright
Figure 4.35: Proper grey reference image for gain correction
5
7
6
5 7
6 6
5 6
4 3 7
3
4
7
1
7 4 6 4
4
3
1
3
4
c
u r r e n t i m a g e
)
5
6
6
5 5
6 5
5 4
4 3 7
3
4
7
1
7 4 6 4
4
3
1
3
4
)
1
1
1
2 - 1
2 - 2
- 1 0
1 - 1 1
- 1
0
2
0
- 1
0
- 2
0
1 1 - 2 - 2 - 2
o f f s e t c o r r e c t i o n
m a t r i x
-
1
1 . 2
1
0 . 9 1
1 . 2
- 2
0 . 9 1
1 - 1 1
0 . 8
1
1
0
1 . 3
0 . 8
1
0
1 1 - 2 - 2 - 2
g a i n c o r r e c t i o n
m a t r i x
=
.
c o r r e c t e d i m a g e
)
Figure 4.36: Schematic presentation of the corrected image using gain correction algorithm
4.6.5 Correction Ranges
Table 4.5 shows the minimum and maximum values of the correction matrices, i.e. the range
that the offset and gain algorithm can correct.
Minimum Maximum
Offset correction -1023 DN @ 12 bit +1023 DN @ 12 bit
Gain correction 0.7 1.69
Table 4.5: Offset and gain correction ranges
.
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