Sunday, July 20, 2008

Croquet Balls

What’s wrong with these croquet balls?

Well one thing you might notice right away is that they’re in pretty bad shape. That’s because they endured a good-natured grudge match between our 14-year-old and Ralph Bakshi at an artist party here a few years ago. Note the chunk missing from the yellow ball.

Here's another photo, this time of a green ball and a yellow ball. I was going to include the blue ball, but someone sent it deep into the woods, and it never showed up again.

By the way, these balls are set up indoors in a shaft of sunlight, and they’re resting on black velvet, so effectively they’re only lit by the sun and each other.

Well, of course you guessed it. The photos have been doctored in Photoshop. I know—my Photoshop skills are about at the level of the Iranian News Agency.

The thing that's wrong with the croquet balls is the color of the reflected light. I switched the left balls in the two pictures, but the ball that was there originally left its telltale color in the shadow of the yellow ball.

Look what happens when we set the balls up in that shaft of sunlight and let their reflected light spill over to an adjacent piece of white board. The light bounces up and to the right. Its influence drops off fairly rapidly as the distance increases from the balls, and the colors intermix in the intermediate areas.

Note, too that the reflected light from the green ball doesn’t have much influence on the adjacent red ball. Their complementary colors cancel each other out.

Here’s a whole color spectrum set up in the shaft of sunlight, again bouncing into the white board. The reflected colors softly gradate from greens on the left to reds on the right. The individual colors in the reflected light are most distinct and separated where the spectrum is close to the board. The yellow area of the spectrum is far from the board, and its effect is mingled with all the other colors into a neutral-colored light at the top of the board.

We can draw at least three conclusions about color in reflected light.
1. Colors of reflected light drop off quickly as you get farther from their source.
2. The effect is clearest if you remove other sources of reflected and fill light.
3. The color reflected into the shadow is a composite of all the sources of reflected illumination, combined with the local color of the object itself.


Murat Kayi said...

I am hereby awarding myself a sunday-bounce-light-cookie, because the green light on the yellow ball struck me as odd...^^ there's still hope for me...:D

Tom Scholes said...

Hahah so mean! I trusted you! I was racking my brain trying to figure out what could cause such a phenomenon :( hehehe.

ricardo said...

Yeah, I figured that out rather quickly. :P
Although, yes, I was sort of puzzled, thinking it couldn't be true that the green ball was reflecting red. :D

Remember that post you added so long ago of a reflecting Christmas ball that'd be used as a guide? I would like to know more about that... you know, the process of using it.