IMAQ vision acquisition does auto white/black level adjustment

[hspec]

Hi,

I am using IMAQ Vision to capture RS170 video from a device we manufacture. I have noticed that the white/black levels seem to be "adjusted" automatically for each image acquisition I make. I would like to turn this feature off, but cannot find a method to do this. Can anyone point me in the right direction?

Thanks,

Howard Spec

CMC Electronics

Canada 

[Christopher W]

Hi Howard,

It sounds like you are turning on the auto exposure before each acquisition.  Are you performing these acquisitions in LabVIEW?  If so, you may be programmatically setting the white and black reference levels.  This is done in the shipping example HL Analog Attributes.vi.  Try performing the acquisitions in Measurement and Automation Explorer (MAX).  If you hit the Auto Exposure button in MAX before each snap/grab, you should see this behavior, otherwise you shouldn’t.

Christopher M.

Applications Engineer

National Instruments

[hspec]

Christopher,

I am not programmatically changing any IMAQ properties or attributes in my Labview code. On the first run I call the IMAQ Grab Setup vi, and from then on I only call the IMAQ Grab Acquire vi. I have played with the Auto exposure button in MAX. That is when I realized that the the levels were being changed during the acquisition in my application. I have looked at the image using a simple monitor and the levels are constant.

Does the IMAQ Grab Setup vi perform an Auto Exposure?  Maybe I only think I am running it once.

Howard

[hspec]

Christopher,

I just looked at my code again and noticed that I am also calling the "IVA Adjust Dynamic vi". Will this perform an auto exposure?

Howard 

[Christopher W]

Howard,

That VI may have similar effects.  If you delete it do you still see the same behavior?  So did you generate your code using the Vision Assistant? If so, what step is that VI included in?

Christopher M.

Applications Engineer

National Instruments