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Programmer: I want you to tell me if you see any apples.
Robot: Describe this thing you call "apple."
Apples are apple-shaped. Look for something that's apple-shaped.
What do you mean by "apple-shaped"?
Well, sort-of round with a dimple at the top and a little stem.
This "stem" is always at the top of an apple?
Not necessarily. The apple might be upside-down or sideways. You must look for stems in all directions.
What if the stem is hidden behind the apple so I can't see it? And what is a stem anyway?
Good point. Forget about stems. Let's start with color. Most apples are red, but then again some are green. I guess a bad apple might even be brown.
Are all things red, green or brown apples?
No! Apples are other things too. For example, most apples are a little bit shiny.
What do you mean by shiny, and how shiny is "a little bit shiny"?
They reflect light well, but not as well as a mirror.
Great. What is a mirror? And what do you mean by "reflect"?
A mirror is something that shows an image of you and what's behind you when you look into it.
I don't know what I look like, or what's behind me - I only have one camera.
Ok, forget about the mirror. You asked what "reflecting" means. Reflecting is when light bounces off of something. If there's a bright light on the apple, you will see a small white reflection off of it.
Got it. So wherever I can find red, green, or brown, and a white spot inside (if it's bright), there's an apple. How can I tell if the light is bright enough that it would make a reflection?
Argh! Never mind! Let's try something else - size. Apples are about 3 inches across.
What do you mean by "about"? If it's 4 inches across could it be an apple? How about if it's 27 inches across?
Let's say all apples are between 3 and 5 inches across.
Is a quarter of an apple still an apple?
Yes, but let's pretend it's not.
What if in front of me there's a red apple sitting on a red table? How can I tell where the apple ends and the table begins? If I can't do that, I couldn't possibly find an apple.
Well, you can see the edge of the apple, right?
Maybe. How do I do that?
The edge is darker than the rest of the apple if there's a shadow, or lighter if there's no shadow and the table is lighter than the edge of the apple, but the apple isn't necessarily a perfectly solid color - I mean there could be dark spots on the apple that aren't edges, and - oh no - there could be photographs of apples on the table which aren't actually apples, or even a wax model of an apple which looks exactly like an apple but isn't, or the apple could have a bite taken out of it, or be really far away so it looks too tiny or too close so it looks really big, or, or... um...
Had enough?
Yes, I think I get your point.

机器人视觉（Robot Vision）简介 article.php?sid=138