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Chapter 2 Basic Acquisition with NI-IMAQdx
NI-IMAQdx User Manual 2-6 ni.com
transferred from the camera to system memory. In all video modes, the ROI
specifies the amount of data decoded by the driver while acquiring into a
user buffer.
By default, the driver transfers the entire image. Specify a smaller ROI for
the following reasons:
• To acquire only the necessary subset of data
• To increase the acquisition speed by reducing the amount of data
transferred and/or decoded
• To allow for multiple simultaneous acquisitions by reducing
bandwidth usage
Note Although you can specify an ROI of any size, the NI-IMAQdx software coerces the
ROI into one that is more compatible for the given camera. Refer to Chapter 3, Advanced
Programming with NI-IMAQdx, for more information about defining an ROI for scalable
images.
Pixel Format
The pixel format specifies the source type of the image format. Different
pixel formats decode into different image types. Refer to the Decoding
section for more information.
Acquisition
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.
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 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.
Note Unlike internal buffers, you are responsible for destroying user buffers.