Use Every Image mode to acquire sequential images. If your acquisition is happening faster than your inspection, the buffers will fill up and so some acquisition steps may fail getting the next image and have to clear out the buffer and start with the first image in the buffer. You could:
1. Increase the buffer size to reduce the chances of this happening. You will still run into this case if your acquisition is faster than your processing, but just not as frequently. Add the following to the Vision Builder.ini file in the [Settings] section if you want to increase the max allowed buffers.
MaxIMAQdxBuffers = <Max Allowable Num Buffers>
It's important to note that IMAQdx only allows user access to half the buffers so if you specify 10 buffers, we can only have access to 5 of them.
2. Reset the acquisition using a Read/Write IMAQdx Attribute step before your acquisition steps to ensure the first three steps always get the first three images of the acquisition. This is probably not what you want since resetting the acquisition can take ~50-100ms.
3. Use a triggered acquisition where you send three triggers for every iteration of your inspection. This will ensure you don't ever get into the roll over case where you exceed the number of buffers you specified.
Also make sure to put a delay to simulate your processing after the third acquisition step. When I just had 3 acquisition steps in a row without anything else I saw the same behavior you described but this is because the first step gets an image that's already been acquired, the second step gets one that is being acquired and the third waits for the image to be acquired (a simple high level rough idea of what is probably happening). If I add a delay equal to the acquisition time*3 after these three acquisition steps, all three steps take about 1-2ms to complete when using the Next Image Mode and the frame index is always sequential (i.e. no missed images).
Hope this helps,
Brad
