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Page 20
TM-6760 Series Progressive Scan Shutter Cameras
3.7 Dynamic Range Control
mV
600
400
200
0
0
The typical interline transfer CCD has fixed noise levels based on dark current (thermal or KT noise),
pattern noise, and the operating clock speed. In general, the level of the 25 MHz pixel clock CCD at
room temperature is around 20 to 50 electrons. The maximum capacity of CCD charges is limited by the
well capacity at saturation. The range is limited by the structure and the pixel size.
The TM-6760 uses a 1/2" CCD with 9.0 µm x 9.0 µm pixel and two-phase vertical shift register
structure. The well capacity is 32,000 electrons. The theoretical dynamic range is 32,000:60 = 533:1
(54.5 dB).
A typical CCD camera does not use the full dynamic range due to the nominal gain and the output
specification such as RS-170. The typical CCD camera's gain is set at 16 to 22 dB and the RS-170 video
level is 714 mV. Using 20 dB gain for the calculation, CCD output is limited to 714/10 = 71.4 mV.
Since the CCD's saturation voltage is 400 mV to 500 mV, it uses less than 1/5 of the full dynamic range.
Machine vision and outdoor applications, cannot afford to miss image information behind the
saturation, which is why the dynamic range adaptation is critical.
3.7.1
The TM-6760 has a built-in LUT (look-up table) for dynamic range control.
At a specific gain setting, the offset (minimum level.... dark point) and A/D reference top voltage
(maximum level... saturation point) are set to 10-bit A/D input so that the full dynamic range of the
CCD is utilized at 10-bit references as the input and the LUT output is converted into 8-bit to adjust the
gamma correction.
The 10-bit input is segmented into two or more regions by the knee-point settings as variable gamma
selection.
LUT selections: (a standard LUT is 20 sets of knee-control LUT)
•
Operation
Max. Digital dynamic range at 3 dB amp
Digital saturation at 16 dB amp
Analog saturation at 20 dB amp
20
40
60
80
LUMINANCE
Programmable Look-Up Table (LUT) and Knee Control
Variable positive Gamma and negative Gamma
Blooming adj. = 13. 5 V
Lens: F=5.6
Vsub = 8 V
Vsub = 10 V
Vsub = 12 V
Vsub = 14 V
Vsub = 16 V
Vsub = 18 V
100
120
160
140
FL
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