JAI TMC-4200GE User Manual download pdf (Page 81)

Page 69

TM-4200GE Hardware

Operation

9.4 Dynamic Range Control

FIGURE 69. Output and Blooming

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-4200CL uses a CCD with 7.4 µm x 7.4 µm pixel and two-phase vertical shift register structure.

The well capacity is 40,000 electrons. The theoretical dynamic range is 40,000:30 = 1333:1 (60 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.

9.4.1 Programmable Look-Up Table (LUT) and Knee Control

The TM-4200CL 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 12-bit A/D input so that the full dynamic range of the

CCD is utilized at 12-bit references as the input and the LUT output is converted into either 8-bit or 10-

bit to adjust the gamma correction. There is no 12-bit LUT.

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 by knee curve direct input.

100

120

200

400

600

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

Vsub = 8 V

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JAI TMC-4200GE User Manual Page 81

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