Thursday, March 13, 2008

Chip Color Balance: How Much of a Difference Does It Make?

Does the RED ONE’s 5000k balanced chip reduce latitude under tungsten light?

Life isn’t easy when one lives with overly intelligent appliances. In my case, my home is “enriched” by Harry the Civil Toaster ("civil" not as in kind, but because he used to be in civil service), an appliance who frequently makes life more interesting than it needs to be.

Yesterday I got home from work to find a pile of potato chips in the middle of the kitchen floor, and Harry in the middle sorting through them one at a time.

“What the heck, Harry!” I said. “What are you doing now?”

“Keep your crust on,” he replied. “I’m in the midst of a great scientific experiment. I read that the RED ONE’s chip is daylight balanced, and I figure if I can find a daylight balanced chip I can probably make my own camera and sell it cheaper!

“Problem is, I don’t know what a daylight balanced chip looks like. I found one that was really, really dark, and my suspicion is that it’s only good for infra-red. I want to start with a full spectrum chip before I get into the esoteric stuff.” He bit into a chip. “Maybe I’m going down the wrong track. Would a daylight chip be corn-based?”

Harry is a highly intelligent toaster. That’s not saying much; any toaster that doesn’t burn Wonder Bread is considered to have an above-average IQ.

“Harry, a chip is a silicon wafer that’s sensitive to light. That’s it. It’s not made of potato or corn. It’s basically melted sand.

“And you can’t tell if a chip is daylight balanced just by looking at it. Most chips are probably balanced for 3200k, as we add an 85 filter when we go outside. What that means is that under 3200k light the chip response in all three color channels (red, green and blue) is relatively equal, resulting in a combination of colors that’s very easy to ‘balance’ so that colors render properly. When shooting under daylight conditions an 85 filter is added because daylight is bluer than tungsten light--and without removing some of that blue, the blue channel will clip long before the other channels do, making it very difficult to white balance.”

“So you’re saying I should be looking for a tungsten chip?” asked Harry, testing another chip. “This one is really salty but it could be hiding a slight metallic taste...”

“Harry,” I said, “you should stick to sourdough. You’re out of your league. You can’t tell what light a chip is optimized for just by taste!”

“Ah, so you’ve tried?”

“No, but...”

“Just keep jabbering, butter boy.” Harry opened a bag of dip chips and dumped them on the floor. “Maybe the ruffles, with their greater surface area, will give me greater sensitivity and resolution.”

I don’t know why I bother, but I do. “Look,” I told him, “I’m not totally sure it makes a difference. There are cameras that can handle daylight situations without an 85 filter. The Sony DXC-D50, for example, has an “electronic” 85 filter that you can turn on for exteriors, but I suspect all it’s doing is reducing the blue gain to bring it in line with the others.

“That seems like a reasonable trick if you can pull it off, but it worries me. My gut says I’ll get better results using an 85 filter, so that’s what I try to do. Fortunately most of the cameras I use have 85 filters built in.”

“Yeah, and luckily they’re all smarter than you are,” said Harry. “Hey, this chip is pretty big. Does that mean it’s higher resolution? I could make a 65mm version of the RED and clean up!’

“You will be cleaning up,” I said, looking at Harry’s chip plant situated on my floor, “but not by selling cameras. And the interesting thing about the RED is that I’m told it’s a 5000k chip. I’m not sure what that means yet.”

“I think it means that it’s manly enough to kick your ass, white bread.” Harry can be very rude sometimes. “Who cares how a chip is balanced anyway? None of these balance very well at all.” He showed me by putting a chip on one finger and trying to balance it. “At best it’s a pale yellow balance, except for the dark ones. Did I say that I think those are infra-red?”

“Yes, you did. The issue with a 5000k chip is that it’s going to get used under tungsten light a lot, which means that the red channel is going to be more saturated than the others. Potentially it will clip sooner than the other channels, and if it does it will severely limit exposure latitude under tungsten light.

“Normally this would be compensated for by reducing the red gain… but the RED is a ‘raw’ camera, and doesn’t have any gain controls. It also doesn’t have a knee circuit to smooth out and desaturate highlights.

“I don’t know this for a fact, but I’m going to test it soon. I’ve already played with someone else’s footage and I’ve noticed that flesh tones do tend to clip sooner than I expect under tungsten light. I can solve the problem by desaturating the image in REDCine, but I don’t always want to be stuck doing that for most tungsten situations.

“It’ll be an interesting test. I’m also curious if I’ll run into problems in the other direction, for example if I shoot a test under skylight at 8000-10,000k. Will the blue clip sooner than the other colors?”

“Beats me,” said Harry. “Maybe a single chip isn’t the answer. Maybe I need an array of three chips. Small chips, like Fritos. Yeah, that’s it. I’m going to the store to get some corn chips.”

“Okay, Harry, and while you’re at it get some bean dip. You’re going to need an A/D converter.”

Harry stopped at the door. “Hey, you’re not so stupid after all, white bread. Maybe I’ll get some guacamole, too. After all, most of the luminance info comes from the green channel… hmmm.”

He spent most of the next hour trying to get his jacket on. Even the simplest task is difficult for a toaster. No opposable thumbs.

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