IMAQdx

[fary]

I am a beginner in labview. i have been trying to make a VI that captures an image at a time using imaqdx.snap. but it gives a black(blank) image in return. i checked the camera result using NI MAX , where snap fuction gives black image in display but grab function works perfectly fine. I have already tried unistalling vision acquisition software and reinstalling it.  

need help urgently 

[Hockeyjim07]

have you looked at your acquisition properties? It could be that the exposure time for snap is to low. 

[fary]

i changed its acquisition attributes, but still getting the same black image. and since i am using the integrated webcam hence the camera attributes has no option such as exposure time, so that i can vary it.

[Hockeyjim07]

what camera are you using? 

[fary]

i am using interated hd webcam 

[Hockeyjim07]

Fary,

This camera is likely working over the USB bus then and must use the DirectShow API in order to be compatible with LabVIEW. Below is a KB discussing this in further detail.

http://digital.ni.com/public.nsf/allkb/4331B4AA3AE95233862574C200539A2F

It is possible that this webcam works perfectly fine but since it might not use DirectShow, it will not be compatible with LabVIEW. If you can determine one way or another if it uses this API please post back.

[fary]

I implemented every method through which i could make sure in time that camera is using directshow API.and then i discovered that people having same laptop model(but running on windows xp )have their snap function working perfectly fine. whereas my OS is windows 8. so there must be some driver issues. i have been searching since for the appropriate drivers but am not yet succeeded. 

[BlueCheese]

Many cheaper webcams have an auto-exposure functiionality that has the behavior you describe where the first few frames are not exposed properly while the algorithm finds the right exposure time. Since a continuous grab sounds like it works, this sounds like your problem.

Some suggestions:

- Disable auto exposure if possible

- Stop using Snap and do a continuous grab if possible. If you are acquiring repeatedly, this will be much more efficient. You could even just pick an image on-demand while the grab works in the background.

- If you want to do a one-shot acquisition still, just do a sequence of enough images just that the last one is properly exposed.

Eric