How to display every other images in image indicator

Question

Hi All,
I am using IMAQ to grab and save high freq and high resolution images. I have an image indicator directly from "Image Grab Acquire". So, the image indicator is displaying every single images at a very high frequency too. We have to display frames, but not necessarily every single one (enough so the operator can see what's going on). So, I am wondering how I can display, say every other images (such as all odd/even number of images), or jump over two and display the third?
Any help will be appreciated!
Thanks!
Wenlong
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Answer 1

Here are some general comments.
Image acquisition is "a horse of a different color" -- unlike many other I/O devices, the memory that holds the data (here called the "buffer") is managed by the driver, and isn't directly available to LabVIEW.
I'm guessing that you are using NI Video hardware, as you are using IMAQ functions (I've only used IMAQdx).  Is this true?  What camera are you using?
The IMAQ Extract Buffer (probably) "clocks" itself to the camera (I say "probably" because I don't know the hardware you are using).  This means that the While loop containing it will run at the frame rate of the camera (hence you can easily calculate the frame rate, as your code shows).
This looks like an NI Demo routine, so I'm guessing that you don't have a lot of experience with Vision processing.  If you've got a lot of other LabVIEW experience, you should be able to make the leap to vision, once you get the idea of how buffers work.  Unfortunately, there's not as much in the way of tutorials and white papers on Vision as on other LabVIEW topics.
So to your question -- how to display every Nth image.  Here's the key loop (which is lifted directly from your code):
As menioned above, this routine is "clocked" by the Extract Buffer function.  What you do to display every N'th image is to put the Image control inside something like a Case statement that "fires" every Nth time.  
Here's an "Nth" version of the above loop (some details omitted) --
We still drive the loop filling every buffer with a frame.  But we then use the Integer Divide function to select the Nth image (those that have a remainder of 0 when i is divided by Nth) and wire the "image" line (it doesn't really hold an image) to the "Image" control, with the other case being "Default" (so all other valeus go there) and with nothing inside.  Thus every Nth time through this loop, the output of Extract Buffer is wire to an Image (and displayed), the other N-1 times the wire goes nowhere.
Bob Schor