Colour verification via usb webcam

[S_Maher]

Hi all,

Bit of a newbie to Labview. can do most simple things but having some trouble when it comes to things that are a little more advanced.

basically I am looking to use a usb webcam for colour verification in a project that I am working on. the part will be placed under the webcam and a snaphot will be taken and as a result of this the part would be moved to the appropriate bin.

have my webcam working in vision assistant and it can take snapshots of the part but after that i am a bit stumped as to what to do as my experience with vision systems etc is limited.

any help would be appreciated 

[Norbert_B]

Well, color is such a subjective thing... very dependend on the lighting!

So IF you can make sure that the images are comparable at all, you are searching for color histograph.

Norbert

[S_Maher]

well i have the lighting issue solved as i have a led ring light around the webcam so shadows/ colour change shouldnt be a problem. but just have no idea how to go about it. have an idea about how it should work but no idea how to implement it. basically take a sample picture/s and store these on computer.

the webcam then takes a shot of the part and compares it to the image already stored and if they are a match the part will pass. would that be correct??

[Norbert_B]

A simple compare between those images will not likely to result in what you are looking for except you can make sure that

a) the DUT is always on the same position (coordinates and rotation and size) in the image per pixel

b) the color always looks alike per pixel information (RGB?)

I doubt that this is achievable. So i would go for color histogram and make some "intervall" around the expected color values. If the DUT is within the intervall, it passes, otherwise, it fails.

Norbert

[S_Maher]

sounds like what im looking for and how would i go about this?? complete newbie to this side of labview im afraid

[Norbert_B]

Color histogram is one function part of the Vision Development package.

[Henrik_Volkers]

A simple way to deal with light and drifts and a simple white light calibration don't work:

Place color standards (could be a good device as a 'gold standard') in the same field of view and compare the results.

Depending on your DUT surface even small changes in light angle can change the result!!

Keep in mind that usual colour webcams calculate the color from three more or less narrow spectral sensitive pictures. ...

[CarlosOtiniano]

Example using a webcam and the module NI Labview IMAQdx

http://www.youtube.com/watch?v=aJCxJLuAhTs