National Instruments NI-IMAQ - Manual (Page 20)

Chapter 3 Programming with NI-IMAQ for 1394
NI-IMAQ for IEEE-1394 Cameras User Manual 3-4 ni.com
Scalable Image Size
IEEE-1394 digital cameras support a predefined set of image sizes which
you can select through the Format and Mode attributes in MAX. See your
camera documentation for a list of supported formats.
If you are using IMAQ Vision, the NI-IMAQ for 1394 software recognizes
the predefined formats and automatically allocates enough memory to
accommodate the image in IMAQ Vision. When you use C or C++ with
NI-IMAQ for 1394 functions, you must know the size of the image for the
selected format and mode to allocate enough memory to contain the image.
You can obtain the size of the image using the Image Width and Image
Height attributes.
Some IEEE-1394 cameras support the Scalable Image Format (format 7),
which allows you to define the size of the acquired image. If you use this
format, you must input the image size using the ROI parameter in
LabVIEW or the Rectangle parameter in C and C++, as shown in
Figure 3-1. The size and position of the sub-image you are acquiring must
be a multiple of the attributes Unit Width and Unit Height, or the driver
acquires the smallest sub-image that contains the ROI you defined.
Figure 3-1. Scalable Image Format (format 7)