Pulnix TMC-1000 Series Manual do Utilizador descarregar pdf (Página 2)

Dynamic Range Control

Typical interline transfer CCDs have fixed noise

levels based on dark current (thermal or KT noise),

pattern noise, and operating clock speed. Typically for a

1k x 1k CCD operating at 25.0MHz pixel clock, the noise

level is around 30 electrons. The maximum capacity

of the CCD charges is limited by the well capacity at

saturation. The range is limited by the structure and the

pixel size.

The TM-1400 uses a 1/2” CCD with 4.65 µm x

4.65 µm pixel and three-phase vertical shift register

structure. The well capacity is 8,000 electrons. The

theoretical dynamic range is 8,000:30 = 267:1 (48 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 has

its gain 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.

Programmable LUT and Knee Control

(patent pending)

The TM-1400 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 bits to be segmented

into three regions. The look-up table selection can be

made either by variable knee curve or by direct input of

the knee coordinates.

Scan Mode

Full Progressive Scan

Normal scanning mode for the TM-1400 is 1392 x

1040 pixels. The standard speed with single-channel

output is 30 frames/sec. at the pixel clock of 50.0 MHz.

(It can also be set to run 15 frames per second at 25.0

MHz.) Unlike an interlace scan camera, the TM-1400

reads every line from top to bottom, resulting in all

lines being obtained per captured image frame with

electronic shutter.

Partial Scan

500 lines and 250 lines partial scan is selectable. It

outputs image center of 500 lines and 250 lines. At 500

lines the frame rate is 56 frames/sec. At 250 lines, it is

99 frames. Standard partial scan control is only available

in 30fps mode.

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

CCD DYNAMIC RANGE VS. VSUB VOLTAGE

Blooming adj. = 13. 5

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

CCD dynamic range utilization

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Linear image: When PCB surface is vis-

ible, metal trace is saturated. If the metal

surface appears, then the plastic surface

is too dark.

Knee-controlled image: The upper

is LUT#6, the lower is #7. Both show

the full dynamic range with differ-

ent effects.

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