SOYO STH-DCAM user manual Subsampling, Subwindowing

STH-DCAM USER’S MANUAL

Both imagers are treated in exactly the same manner. It is not possible to set a different exposure or gain on each imager.

Digitization control can operate in either manual or automatic mode. Refer to Figure 6-1for the controls in the video capture program.

In manual mode, the user program sets the exposure and gain. The exposure and gain are based on a 0 to 100 scale. Here are some tips for setting exposure and gain.

•In general, keep the gain as low as possible, since it introduces additional noise into the system. Use it only if the exposure is set to maximum, or if the exposure must be kept low to minimize motion blur.

•Adjust the manual iris of the lens to as small an opening as possible for your application, without having to use gain. This will increase the depth of field and give better optical performance.

6.3Subsampling

In many applications it is not necessary to work with the the full 640x320 pixel array. The CCD image processors are capable of reducing the amount of information contained in the digital video stream sent back to the host. They do this by averaging the values from neighboring pixels, giving a higher signal-to-noise ration. This technique is called binning. Binning occurs automatically when a smaller frame size is selected.

Figure 6-2shows the frame size control on the video capture application. The two frame sizes allowed are 640x480 (full frame) and 320x240 (x2 binning).

6.4Subwindowing

The STH-DCAMs do not support subwindowing..

2001 VIDERE DESIGN

Figure 6-2 Frame size control in the main capture window.

6.5Frame Rates

Frame rates from the STH-DCAM depend on the frame size and color mode. Frame rates can be set under program control with the SetRate() function; see the Small Vision System User’s Manual. For the smallv and smallvcap applications, frame rates are set at 30 Hz.

Frame Rates, Hz	Monochrome	Color
320x240	30, 15, 7.5	30, 15, 7.5
640x480	30, 15, 7.5	30, 15, 7.5

Table 6-1 Allowable frame rates for the STH-DCAM in different

modes.

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