National Instruments IEEE 1394 用户手册

Both high-level and low-level functions support snap, grab, sequence, and 
triggered acquisitions. Using high-level functions, you can write programs 
quickly without having to learn the details of the low-level API and driver. 
The low-level functions give you finer granularity and control over the 
image acquisition process, but you must understand the API and driver in 
greater detail to use these functions.

The high-level functions call low-level functions and use certain attributes that are 

listed in the high-level function description of the NI-IMAQ for IEEE 1394 Cameras 
Function Reference Help. Changing the value of these attributes while using low-level 
functions affects the operation of the high-level functions.

This section describes the basic steps of performing an acquisition with the 
NI-IMAQ for IEEE 1394 Cameras software. The basic steps are 
initialization, configuration, and acquisition.

To acquire images using the high-level or low-level functions, you first 
must initialize a camera session. A camera session is a process-safe handle 
to an IEEE 1394 camera. The driver uses a camera session to identify the 
camera to which further NI-IMAQ for IEEE 1394 Cameras functions apply. 
You can simultaneously open as many camera sessions as there are cameras 
connected to you system.

When initializing the camera session, you need to specify two parameters: 
camera name and camera control mode. Refer to the following sections for 
detailed information about these parameters. When an application is 
finished with the camera, call the Close function to close the camera 
session.

NI-IMAQ for IEEE 1394 Cameras references all camera sessions by a 
name. The driver creates default names for each camera in your system in 
the order that the cameras are connected. The names observe the 
convention shown in Table 2-1.