Photon Focus CameraLink MV1-D1312 series User Manual page 36

4 Functionality
:
a v e r a g e
o f g r a y
r e f e r e n c e
p i c t u r e
Figure 4.22: Schematic presentation of the gain correction algorithm
Gain correction always needs an offset correction matrix. Thus, the offset correc-
tion always has to be performed before the gain correction.
How to Obtain a Grey Reference Image
In order to improve the image quality, the grey reference image must meet certain demands.
• The grey reference image must be obtained at uniform illumination.
Use a high quality light source that delivers uniform illumination. Standard illu-
mination will not be appropriate.
• When looking at the histogram of the grey reference image, ideally there are no grey
levels at full scale (1023 DN @ 10 bit). All pixels that are saturated white will not be
properly corrected (see Fig. 4.23).
• Camera settings may influence the grey level. Therefore, the camera settings of the grey
reference image must be identical with the camera settings of the image to be corrected.
Figure 4.23: Proper grey reference image for gain correction
34
1 4 2 3 3
1
-
1 0
3 7 9 7
1
6
1 8 7 1 0
- 2
4 9 7 9 1
1
4 9 6 8 4
1
g r a y r e f e r e n c e
p i c t u r e
)
)
1 - 1 0 0
- 1 2 0 0
=
- 1
2 1
- 1
- 1 0 2 - 2
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 - 1 0 0
1 1 0 . 8
0 . 9 1
- 2 1 . 2 1 . 2 0 . 8 1 . 3
1 0 . 9 1 1
1
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