Gray point

PE
Posted By
phoney.email
Apr 10, 2004
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170
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1
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This is a bit theoretical but I hope someone can chime in…

I never really understood how gray point worked, so I decided to create a range of fills, apply gray points, and plot the results in an Excel sheet.

Well, I’m now even more confused… 🙂

For one, Levels gray point and Curves gray point do different things. (I confirmed this by Apply Image/Difference). In general, Curves seem to add more contrast (and that’s all without touching black and white points, just the gray!)

Anyway, can anybody throw some light on how Levels and Curves calculate the gray point?

Don.
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TA
Timo Autiokari
Apr 10, 2004
(Don) wrote:

how Levels and Curves calculate the gray point?

They do it incorrectly, do not use the gray buttons.

To set the gray balance:

1) drop a sampler (in 5×5 mode) over a an area that was gray in the real scene.

2) Have the Info palette visible, note the smallest value of the R, G and B of that sampler.

3) Using the Levels dialog, adjust the right *output* slider (output scale is the bottom most thing in the dialogs) of the two channels that are higher than the smallest value so that the sampler shows R=G=B ==smallest.

4) Now, do not exit the Levels dialog, just select the ‘RGB channel’ and scale the right input slider downwards (image gets more bright) but do not clip image data. Then press OK to the Levels dialog.

Timo Autiokari http://www.aim-dtp.net/

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