Data Translation DT3153, User Manual

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Principles of Operation
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Passthru
The DT3153 board can continuously capture and display video data;
this operation is called
passthru . The goal of passthru is to allow you
to view images (in as close to real time as possible for the
configuration and passthru method chosen) for the purpose of
focusing or positioning the camera.
In a passthru operation, the image is captured, converted to a bitmap,
and transferred to the display memory of the video board. Image
data in display memory is continuously overwritten and is not
stored.
This section describes the following aspects of passthru:
• Bitmap passthru mode,
• Source origin,
• Passthru scaling, and
• Overlays.
Bitmap Passthru Mode
The DT3153 board supports both synchronous and asynchronous
bitmap passthru mode. In a synchronous passthru operation, you
cannot perform another operation until the synchronous passthru
operation is stopped. In an asynchronous passthru operation, the
operation starts but gives control to you immediately, allowing you to
perform other operations while data is displayed.
Bitmap passthru mode requires a frame in device memory into which
the image is first captured. Once it is captured, Windows functions
perform bit copies of the image data to display memory. Windows
functions handle obstructions to the passthru window by
automatically clipping the passthru image to the visible client
window region. Therefore, even if the window is obstructed, the
passthru can continue unabated. Once an obstruction has been