JAI TM-1325 Series, User Manual

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Operation 15
TM-1325 Series
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 55 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-1325 uses a 2/3” CCD with 6.45 μ m x 6.45 μ m pixel and four-phase vertical shift register structure. The
well capacity is 16,000 electrons. The theoretical dynamic range is 16,000:30 = 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 9 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-1325 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 10 sets of knee-control LUT)
•
Variable Gamma
•
Variable knee curve
•
Direct input LUT