> > The original tutorial that I was following at
> > http://digital-photography-school.com/precise-color-cast-correction-with-gray-fill-layers
> > had the user add a temporary 50% Gray Layer (7f7f7f), Mode: Difference
> > to find a gray point. I manually picked the point, wrote it down on a
> > piece of paper, and then relocated that point in the Levels Dialog. I
> > had asked the question, is there another way to remember this x/y
> > location. This is where the Sample Points Dialog was suggested to
> > record the location, I think, rather than writing it down on a piece
> > of paper. It's a nice idea and Dialog.
> Probably the easiest way to mark a point is to use two rulers. But sure,
> the sample points can also be used for that.
> The grey-point picker in the GIMP levels tool doesn't require you to
> pick a perfectly gray point though. It is totally sufficient to pick a
> point that is supposed to be some shade of gray. Basically any surface
> that should be white will do it. The actual luminance is not relevant.
That is very useful to know, thanks.
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