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Can you adjust white balance in a digital image using Photoshop (or similar) in such a way that average blurring the entire image gives gray (R=G=B)? Note, I'm not necessarily looking to achieve "correct" color balance with this method.

  • How would that work? E.g. if I take a photo of a red flower, that flower will be red (or purple, or yellow,...), but never gray, with white balance. It could only work if you have equally sized areas of equally "intense" (as in RGB-values) colors. – flolilo Feb 23 at 17:21
  • @flolilolilo What OP is asking for is a more generic form of colour correction than what is usually encompassed by 'white balance correction'. I have no clue what he needs it for, but it is technically feasible. You might have to adjust the saturation and not just apply a colour filter. – jarnbjo Feb 23 at 17:48
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    What problem are you trying to solve? – osullic Feb 23 at 19:11
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    This is essentially how auto white balance works. – Wirewrap Feb 23 at 21:01
  • @osullic No problem except the one described. It's an academic exercise if you must know. Trying to convince myself that most images that average to gray are correctly color balanced as this is the principal used in analog color printing -- that a typical scene when projected and diffused will produce gray if correctly balanced. – bvy Feb 24 at 17:15
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No.

Unless the subject is a perfect neutral color object.

Take a photo of the leaves of a tree... the average will probably be green (depending on the season of course) Take an underwater image, and probably blue will be the dominating color.

enter image description here

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Can you adjust white balance in a digital image... in such a way that average blurring the entire image gives gray (R=G=B)?

Yes.

But why would you want to do that? It's easier to desaturate.

The following image made by adjusting colors and curves, not by decreasing saturation.

image


Can you adjust white balance in Photoshop based on average blur?

Yes.

It's a useful technique to try with difficult images, but results likely won't be what you're after. (Guassian blur original with radius 500; color layer blend result with original at 50%; adjust curves and color.)

original modified


... a typical scene when projected and diffused will produce gray if correctly balanced.

No.

Anyone who has seen diffuse colored light reflected from a projector screen has seen a demonstration that this isn't true.

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