Think like a vision system

Regular readers know that I’m a big believer in the value of education, so it will be no surprise that I’m recommending the first-rate machine vision primer from Greg Hollows and Glenn Archer, published in the May ’08 Assembly magazine. (Unfortunately I can’t find a way to link directly to the article, so you’ll need to open up the digital version of the May edition.)

However, regulars will also know that I can never resist point out an opportunity for improvement, so here it comes.

The weakness with this article is that it focuses (yes, that’s a deliberate pun,) on hardware rather than on solving the application. The guys note that lighting is the “most critical and least understood factor,” but they don’t discuss what you’re trying to achieve with the lighting. Perhaps that needs a separate article, but I can sum it up in one word: contrast.

OK, maybe it needs a few more words, so here’s a slightly better explanation. Your vision system “sees” only grayscale values – all it knows about the scene is a matrix of numbers – it has no inherent ability to understand what it’s looking at, so you have to make it very obvious. This means you need to light your target to create a strong contrast between what you want to see and what you don’t. Think like a vision system and not a human.