Two questions about white point/black point in curves adjustment layer

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  • Updated 2 years ago
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I have two questions about using the white point/black point ends of the curve in a curves adjustment layer.

If you click the triangle shown here, you change the mapping of which RGB level maps to white (255/255/255). I use this all the time at both ends of the curve.

First question.
If you want to know what the actual numbers are of the adjustment, or just want to tweak the adjustment by 1 or 2 levels, you need to click on the point or the triangle. However, 9 times out of 10, you end up changing the level when you click on it, and often you can't even see that you changed it.

Q: Is there any way to select the point, or the triangle, without inadvertently changing the values?

Second question.
If you hold down the option key while moving the triangle, Photoshop will show which pixels (in each of the RGB channels) are being clipped, which I find to be very useful. However, the feedback of which pixels are being clipped is not accurate. If you drag the triangle to the left a few pixels, and then drag it to the right, different pixels will show as being clipped. There is some kind of hysteresis in the feedback, and the same values (Input/Output) will show different pixels being clipped depending on the history of how you have dragged the triangle.

Q: Is this a known bug in Photoshop? Is there any way to get an accurate preview of exactly which pixels are clipped at any given input/output value?

I can post the second as a bug, but it will take some work to show it (as it is difficult to take a screen shot while option-dragging). And since this bug (or perhaps just an "infelicity") has been around for a number of years, I suspect that Adobe will not prioritize addressing it, since they, not surprisingly, don't seem to want to address bugs that have not generated numerous complaints.
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Alan Harper

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Posted 2 years ago

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Cameron Rad

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First question:
Shift + Control + Click

Second Question:
Maybe try setting cache level to 1, although this will slow down your general performance. 
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Alan Harper

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Thanks for the response, Cameron. I had forgotten that the control modifier can have various effects in Adobe programs. Sometimes it means "move smoothly, don't be 'sticky'" -- in this case it appears to mean "don't move when selected." AFAICT, it is control, not shift + control, and it only works when clicking on the point, not on the triangle. But that does solve my problem.

The cache levels didn't seem to affect the second issue. At least, I moved the setting from 4 to 1, relaunched Photoshop, and the problem wasn't resolved.