12.2 Image Correction
:
7
1 0
9
7
9
7
8
7
9
4
3
2
3
4
1
1
9
6
8
4
6
1 0
1
3
4
g
r a y r e f e r e n c e
p i c t u r e
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
)
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
=
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
g a i n c o r r e c t i o n
m a t r i x
Figure 12.3: 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 detailed procedure to set the grey reference image is described in Section
C.6.
•
The grey reference image must be obtained at uniform illumination at about 70% of the
saturation level.
Use a high quality light source that delivers uniform illumination. Standard illu-
mination will not be appropriate.
•
If
PreGain
is correctly set, so that the saturation level is at 4095 DN (@ 12 bit resolution),
then the grey reference image should have a mean between 2400 and 3200 DN (@ 12 bit
resolution). If PreGain is set to 1.0 then the mean of the grey reference image should be
between 1500 DN and 2000 DN (@ 12 bit resolution).
•
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.
•
The grey reference image is stored in the camera by sending the command
Correction_SetGreyRef
.
12.2.4
Defect pixel correction
Calibration
The positions of the hot and cold pixels are determined in the
Calculate
step.
Defect pixels are identified:
•
Using the grey reference image: every pixel with an intensity value below the
cold-pixel-threshold or above the hot-pixel-threshold is marked as a defect pixel.
MAN093 08/2021 V1.1
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Summary of Contents for MV4 Series
Page 8: ...CONTENTS 8 of 143 MAN093 08 2021 V1 1 ...
Page 12: ...1 Preface 12 of 143 MAN093 08 2021 V1 1 ...
Page 40: ...4 Image Acquisition 40 of 143 MAN093 08 2021 V1 1 ...
Page 42: ...5 Exposure Control 42 of 143 MAN093 08 2021 V1 1 ...
Page 52: ...6 Counter Timer 52 of 143 MAN093 08 2021 V1 1 ...
Page 64: ...10 Image Format Control 64 of 143 MAN093 08 2021 V1 1 ...
Page 66: ...11 Frame Rate 66 of 143 MAN093 08 2021 V1 1 ...
Page 82: ...12 Pixel Data Processing 82 of 143 MAN093 08 2021 V1 1 ...
Page 92: ...12 Pixel Data Processing 92 of 143 MAN093 08 2021 V1 1 ...
Page 96: ...13 Precautions 96 of 143 MAN093 08 2021 V1 1 ...
Page 120: ...16 Troubleshooting 120 of 143 MAN093 08 2021 V1 1 ...
Page 126: ...19 Support and Repair 126 of 143 MAN093 08 2021 V1 1 ...
Page 128: ...20 References 128 of 143 MAN093 08 2021 V1 1 ...