Ring

Table of Contents

1. Description

2. Common Applications

3. What To Expect

1. Description

A ring is a continuous, high-speed acquisition to multiple buffers in memory.

Basic steps in performing a ring acquisition are as follows:

• Initialize the interface

• Select and allocate the number of buffers necessary to ensure that no frames will be lost under the worst case of processing and operating system delays

• Create an acquisition loop in which one of the buffers is locked out of the acquisition and made available for processing

• Perform the processing and/or display on the locked-out buffer; release the buffer and lock out the next frame's buffer

• Close the image acquisition session and free the memory allocated during the acquisition

Grab vs. Ring Acquisitions
A grab acquisition before NI-IMAQ 3.0 used a single acquisition buffer to store acquired images, while a ring typically used multiple buffers in a circular acquisition scheme. With NI-IMAQ 3.0 and later, a grab is now implemented as a 2 buffer ring. The grab requires the acquisition buffer to be copied for subsequent processing, in order to allow the acquisition to continue while the processing is being done. Since a ring has multiple buffers, the processing can be done in place in the acquisition buffer, eliminating the need for copying.

Prior to NI-IMAQ 3.0, a grab acquisition could result in "split" frames, where a single output image contained information from adjacent frames. NI-IMAQ 3.0 and later remove this problem because the grab is implemented as a 2 buffer ring.

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2. Common Applications

The ring acquisition is appropriate for continuous high-speed applications which require processing on every image.

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3. What To Expect

A continuous display of processed images
Related Links:
Ring Acquisitions
Multi-Camera Acquisition
NI-IMAQ Driver