Acquired image frame brightness changes for static lighting and camera parameters

[PierreB]

I have a VBAI inspection which acquires a single frame from an AVT Pike 505-C using the 'Acquire Image (1394, GigE, or USB) step. The acquisition occurs without issue and the VBAI inspection runs fine, however over time the brightness of the source frame acquired changes. At first I thought I might have a parameter set to 'Automatic' or something which was trying to dynamically adjust for lighting conditions but the closest thing I can think of that would be doing this is having the shutter set to 'Relative'.

When frame acquisition is manaully toggled through Measurement & Automation Explorer  it exhibits the same behavior, however when I use the AVT acquisition software (SmartView) I do not have this issue. I've tried the following items to correct this:

- Upgrading to the latest NI Vision Acquisition drivers 

- Upgrading to NI VBAI 2009

- Set all camera parameters to 'Ignore' in the VBAI Acquire Image step

It would seem that I have missed some parameter menu somewhere that would allow me to configure this camera to acquire images with a constant brightness given a fixed optical train and light source with a fixed intensity. Can someone point me in the right direction?

[The_Chancenator]

Hi Pierre,

The camera attributes are actually going to depend on the camera file that is pulled from the camera itself.  You said that the camera also experiences this behavior in MAX?  Is this when you are doing a series of snaps that you see this behavior?  What about if you are doing a grab?   Also, do you know if it is just in the display of the image, or is inherent of the actual image itself (you may be able to do a histogram or something on the acquired images and see if it is shifting over time)?

Secondly, are you using any kind of strobe or light accessory with the camera?  This could be changing over the acquisition too.  

I'd say start with the camera attributes in MAX and see if any of those seem to pertain to the issues that you are seeing.  If not, then move on to testing it with the histogram.  If this doesn't work we can keep troubleshooting. 

Cheers, 

[BlueCheese]

Hi Pierre,

Note that with the 'mode' parameter of the various DCAM attributes set to 'Ignored', it means that IMAQdx does not modify them. This is more designed for cameras that are buggy and where those registers don't work in the expected manner. What this also means is that you will be getting the camera's default settings when you open the camera in IMAQdx (which might have been modified in AVT's software and saved into the camera). Thus, the camera might actually be in an 'Auto' mode for some attribute like brightness.

I would suggest you put all the attributes into a Manual mode to ensure they stay fixed. The term 'Relative' refers not to an automatic mode but rather to a manual mode where the value parameter is a relative value between the camera's minimum and maximum for that feature (as in it has no defined units other than what the camera's own manual might define their interval to be). This is in contrast to Absolute mode where the units are defined in real-world units.

Eric 

[Andrey_Dmitriev]

Probably "brightness changes" are just visual changes caused by 16 to 8 bit mapping (if you have more than 8 bpp image)? Try to measure real intencity in the images.

Andrey.

[The_Chancenator]

Hi Pierre,

Adding to BlueCheeses post, I noticed that your camera has "Auto controlled gain, exposure, white balance"--this may be causing the behavior you are seeing.  See the specs PDF:http://www.uniforcesales.com/docs/avt/specs/PIKE_F_505B_C.pdf

Cheers, 

[oliver.guennel]

Do you mean changes from image to image or does the image brightness change after starting e.g. the application a second time?

For the first case, only the automatic modes or an unsynchronized illumination could be responsible.

We know the second effect in some cases, where it was related to the camera-built in Gamma correction. There was a misinterpretation of the feature as the driver writes it into the camera and the way the camera “understands” it. Initializing the camera a second time, set the correct value. I have only seen this effect with the Legacy 1394 driver. In the (latest) IMAQdx driver is disappeared.

The solution for the issue was to set the Gamma feature in MAX to “off” instead of "0".