Sunday, April 10, 2011

Stay away from color!

Those new to machine vision are often tempted to reach for a color camera to solve their inspection problems. This is probably because most of us see in color, but I don’t think it helps that the camera companies like to trumpet the arrival of every new color product from the rooftops. This just encourages the habit of grabbing the color cam rather than the monochrome. (Yes PPT, I am talking to you! “PPT VISION introduces twenty-six new IMPACT M-Series color cameras… ”)

So I’m here to tell you to avoid color at all costs. Color machine vision is really challenging, for more than a few reasons. Perhaps the biggest is that our human perception of color correlates poorly with the actual wavelength of reflected light. The color of a surface is also heavily dependent on it’s texture, it’s orientation to the incident light, and of course the spectrum of the light used for illumination. (And please don’t try to do color vision with a red LED lighting – yes I have seen it attempted!)

Then there are all the problems with processing color images, plus the loss in resolution: is the edge at the green pixel or the red one? Color is just a real headache and should only be attempted by those with years of experience. In fact to support this point, note that the AIA’s Certified Vision Professional program deals with color in the Advanced category!

Have I put you off or are you still leaning towards a color camera? If you are, then read “Color Vision: Luck Has Nothing to Do With It” by Winn Hardin and published on the AIA web site, March 7th, 2011. This is a good article that goes into more detail than I have time for. If you really want to work with color at least go into it with your eyes open.


makc said...

Don't see why. If you know the color of object you're looking for, you can discard most of pixels in the image and resort to simplest algorithms. I am completing an app right now that tracks two different colored gloves. Doing the same in grayscale would be much harder, if at all possible.

Logan Cale said...

Matrox Imaging just released a white paper on this topic....