Pulnix TM-4000CL Series Manuale Utente Scaricare il pdf (Pagina 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 2k x 2k CCD

operating at 40MHz pixel clock, the noise level is around

50 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-4000CL uses a 1.2” CCD with 7.4 µm x 7.4 µm

pixel and two-phase vertical shift register structure. The well

capacity is 42,000 electrons. The theoretical dynamic range

is 42,000:50 = 840:1 (58 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-4000CL 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-4000CL is 2048 x

2048 pixels. The standard speed with dual-channel output

is 15 frames/sec at the pixel clock of 40.0 MHz*. Unlike

an interlace scan camera, the TM-4000CL reads every line

from top to bottom, resulting in all lines being obtained per

captured image frame with electronic shutter.

Partial Scan

Partial scan has 3 scan options from which you can

select: 1000, 500, or 250 lines. It outputs image center of

1000 lines, 500 lines and 250 lines. At 1000 lines the frame

rate is 28 fps. At 500 lines, it is 50 fps, and at 250 lines it is

80 fps.

Dual Tap Output

The TM-4000 has built-in line buffers to select channel

B output direction. CCD output is split into two channels.

The left half outputs data from 1 to 1024 (ch.A) and the

right half outputs from 2048 to 1025 (ch.B). The internal

line buffer corrects the right half (ch.B) output to start from

1025 to 2048 so that frame grabber does not have to convert

the pixel orders. The output order is selectable.

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 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

CCD dynamic range utilization

Linear image: When the PCB surface

is visible, the metal trace is saturated.

If the metal surface appears, then the

plastic surface is too dark.

Two different knee-controlled

images: Both show the full

dynamic range with different

effects.

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Pulnix TM-4000CL Series Manuale Utente Pagina 2

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