Справочник Пользователя для National Instruments IEEE 1394

Although you can specify an ROI of any size, the NI-IMAQ for IEEE 1394 Cameras 

software coerces the ROI into one that is more compatible for the given camera. Refer to 
Chapter 3, 

, for more 

information about defining an ROI for Format 7 images.

After configuring and starting your acquisition, the camera sends data to 
the internal buffers. To process the acquired image data, you must copy the 
data from the internal buffer into your user buffer.

Before starting the acquisition, you must allocate a user buffer in addition 
to configuring internal buffers. The driver copies or decodes image data 
from the internal buffer into the user buffer during acquisition. Then, 
process and analyze the image in the user buffer.

When acquiring data into an IMAQ Vision image, the driver resizes and 
casts the image as needed. However, if you acquire data into a user buffer, 
you must allocate enough space for one decoded image.

Unlike internal buffers, you are responsible for destroying user buffers.

A buffer number is a zero-based index that represents the cumulated 
transferred image count. For example, during a continuous acquisition with 
three internal buffers, the buffer number is updated as follows: 0, 1, 2, 3, 4, 
5, and so on. Buffer numbers 0 and 3 refer to the same internal buffer in the 
buffer ring.

For a one-shot acquisition, you can request only one of the available buffer 
numbers. For a continuous acquisition, you can request any present or 
future buffer number. You can also request the next logical buffer or the 
buffer containing the most recently acquired data. With high-level grab 
acquisitions, the buffer number defaults to the next transferred buffer.

When you complete the buffer acquisition step, the driver returns the actual 
buffer number with the image.