JAI TM-1020 - Manual (Page 36)

Page 26
TM-1020 Series Progressive Scan Shutter Cameras
Operation
3.7 Dynamic Range Control
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 20 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-1020 series uses a 1” CCD with 9.0 µm x 9.0 µm pixel and two-phase vertical shift register
structure. The well capacity is 50,000 electrons. The theoretical dynamic range is 50,000:30 = 1667:1
(64 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 Programmable Look-Up Table (LUT) and Knee Control
The TM-1020 series 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 look-up table has two knee points (variable gamma selection) that allow the 10-bit input to be
segmented into three regions. The look-up table selection can be made either by variable knee curve or
by direct input.
0 20 40 100 60 120 80
0
200
400
600
FL
Lens: F=5.6
Vsub = 10 V
Vsub = 12 V
Vsub = 14 V
Vsub = 16 V
Vsub = 18 V
CCD OUTPUT VOLTAGE
LUMINANCE
Blooming adj. = 13. 5 V
Digital saturation at 16 dB amp
Analog saturation at 20 dB amp
Max. Digital dynamic range at 3 dB amp
140 160
mV
Vsub = 8 V