"Buffer Number In"

[ceger]

The help documentation for IMAQ1394 Get Image and IMAQ1394 Get Image data (for IMAQ 2.0.2) both describe the Buffer Number In parameter as follows:

"Buffer Number In is the cumulative image number to get.  A value of -1 gets the most recently acquired buffer.  A value of -2 gets the last acquired buffer."

Huh?  What's the difference between "most recently acquired" and "last acquired"?  These terms seem synonymous to me.

If I've allocated 5 buffers for continuous acquisition (A, B, C, D, and E) and the acquisition process has wrapped the buffers once and is currently acquiring buffer 7 (corresponding to buffer location C), which buffer will be returned if I call Get Image with -1 for Buffer Number In?  And for -2?

[David S.]

Hi ceger -

This confusion has been mentioned before, and we're working on a better way to word that documentation for future releases of the driver.

A value of  -1 means that the function will wait for the current buffer being acquired to finish and then return that.   A value of -2 to means that it will simply return the the last entire buffer that has already been acquired into memory.

So if you have this function in a loop and give it -1 for the buffer number, the loop will iterate at the rate at which frames are coming in, and each frame will be a new image. If you have -2 for the buffer number, the loop will iterate as fast as it can, and it will get the same image until the next one has been fully acquired.

[ceger]

Thanks!