# Auto WB 18% gray RGB values



## millerstreet (Jan 28, 2012)

While I'm fairly sure this won't be an easy answer from the arcane math equations on RGB values and 18% gray, however does someone have approximate values for the eyedropper tool in LR3 for percentages? I'm coming close with the 76%-77%-76% range, and using a gray card in some of the bball venues just doesn't work (light is too varied).  I'm trying to see if I can find a percentage range or very close value to search the photos for to hit on that neutral.  Am I making this waaay to difficult? Probably...  

Let me know if anyone has some info?


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## Hal P Anderson (Jan 28, 2012)

Yes, you're overthinking the problem, and your thinking is wrong...

The numbers don't matter. You don't even need an 18% grey. You have to click with the eyedropper on a part of the image that is neutral grey _in real life_, not in the image on your computer. 

The whole idea is that the light that illuminated the scene has some kind of cast to it, and that grey card (or grey dress, or white shirt in shadow) doesn't look grey in the picture because the light shining on it isn't white light. By clicking on that patch with the eyedropper, you tell LR to _make_ that patch grey, and to adjust the colour in the rest of the image as if the scene was illuminated by white light.

If you click on a place in the image that is grey in the image (R=G=B), absolutely no white balancing will take effect. If the patch in the image is already grey, there is nothing LR needs to do to make it grey, so it does nothing.

Hal


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## erro (Jan 28, 2012)

And the trick is also to decide what part of the image should have the "correct" white balance. A person wearing white shirt in daylight (sun) will have two shades of white: white (in the sun) and grey (in the shadow). The white will hopefully not be a blown out white, but a white with some details in it, but it should probably be a pure white anyway (no color cast). The shaded part of the shirt will not be pure grey though, since it is not illuminated by the sun directly, but rather by reflected light from the blue sky, green grass, a red wall or whatever. Making that "white in the shade" neutral will make you sunlit whites go the other way in color.


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## Mark Sirota (Jan 28, 2012)

Right -- the short answer, with the WB eyedropper, click on something that _should be_ white.

Ideally, you want to clip on something that is (in real life) bright white, but be sure that none of the channels are clipped.

A grey card will work, but not as well as a proper white balance target. Grey cards are not always color-neutral, and you'll get more accurate results from something brighter.


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