R/G/B gain -- makes no sense at DVinfo.net

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Old July 21st, 2006, 12:25 PM   #1
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R/G/B gain -- makes no sense

Where I come from, Red and Cyan are opposite colors. Green and Magenta are opposite colors. Blue and Yellow are ooposite colors. But in the HD100, G gain increases BOTH green and megenta. B gain increases BOTH blue and yellow, etc. HUH?!?!?! This seems completely counter-intuitive and seems to defeat the whole notion of color adjustment.

Put another way... if I want to increase yellow, I DON'T want to increase blue.
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Old July 21st, 2006, 12:54 PM   #2
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Yellow = R + G

The primary colors of emitted light are Red, Green & Blue
Cyan = Blue + Green
Magenta = Blue + Red

Try it with any computer program that lets you define a color with RGB values.
To get "more" yellow, you can either increase Red and Green .... or decrease blue.
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Old July 21st, 2006, 07:22 PM   #3
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It makes more sense if you look at it on a vectorscope. The camera's not doing these color transformations in RGB color space, but rather in YUV color space. Watch the vectorscope, when you twiddle the R gain control, it's actually scaling the entire vectorscope plot along the axis defined by the color red, so colors on the opposite side of the vectorscope from red are affected as well.

Counterintuitive? You bet.
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Old July 21st, 2006, 07:43 PM   #4
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Find some information on floating white point. It seems counterintuitive however it keeps the entire color space inside the gammut of ITU709. The opposite would be absolute white point which would affect a color individually without affecting the other colors (when adjusted).

These are two different ways to adjust color in relationship to white.
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Old July 21st, 2006, 11:41 PM   #5
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Bill, as Stephen has suggested you have to look at the gain using a Vscope. In that way you'll see that not only the gain of Red, for example, affects blue, but also that by increasing the gain you cause a shift in the rotation. Take a look at my articles about the TrueColor configuration, there are some snapshots of a Vscope. The easiest, IMHO, way of making sense of it is to use a DSC chart and a Vscope and tweak the gain *and* rotation.
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