Can you "De-couple" Levels sliders?

BL
Posted By
Bill_Lamp
Apr 5, 2004
Views
368
Replies
3
Status
Closed
I have checked the manual, FAQ, and tried a search under "Levels".

The Fuji-S2 starts to pick up blue noise in shadows ( beginning to be a problem around 4-5 stops under exposed). This is from some tests I have seen on-line by people who are far better able to do this type of testing than I am. There is also some red noise (less and beginning at about the same EV) but, for my work, this is FAR less objectionable.

I have noticed this when doing drastic enlargements and have been controling it by moving the left blue level slider to the right to chop/force to solid color that section and then try to move the middle slider back to the original mid point to avoid an overall color shift.

Is there a way to de-couple the levels sliders so you can move one end without the center one moving?

If not:

If I move the left slider 10 units right, is a 5 unit left the proper correction to move the center slider back to it’s original position? (Those numbers were used to make the math easy.)

OR

Is this best handled in Curves?

Thank you.

Bill

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RW
Rene_Walling
Apr 5, 2004
Is this best handled in Curves?

As a rule, curves give you a lot more control than levels, so I would say yes, it is better handled that way.
GA
George_Austin
Apr 5, 2004
Bill,

The middle slider is inherently changed when either end slider is moved. The original middle slider position is not necessarily desirable after you have changed an end slider position. Photoshop’s correction of the middle slider adjusts the power curve (which the middle slider represents) to best approximate its new shape, but the adjustment cannot be exact because PS is trying to construct a power curve to match a curve comprised of two linear segments—one segment going horizontally from a corner to the end slider position and the other angling from the end slider position to the opposite corner. Photoshop constructs a power curve that best fits that segmented line pair, and that is a better representation of the input-output relationship after the end slider is moved. You ought not decouple these sliders, but if you don’t like the result you can then tweak the middle slider. The end sliders are not affected by moving the middle slider, despite the fact that the middle slider is affected by the end sliders. You seem to be looking for a fixed relationship between middle and end slider movements, but there isn’t one. The relative movements will vary depending on the magnitude of the end slider movement.

George
BL
Bill_Lamp
Apr 6, 2004
George,

Thank you for the information on just how the sliders work and what they represent. For most images, Levels, on the combined channels, is the first tool I use especially with low brightness range images.

From what you and Rene have written, I would be getting better results by controling those pesky pixels with the blue channel curve.

As a side note, I am very satisfied with the camera and have a far easier time with it’s images than I do with the film N-90 and the LS-40 scanner (Hamrick software 4 to 8 x multi-pass multi-scan).

Thanks again.
Bill

Must-have mockup pack for every graphic designer 🔥🔥🔥

Easy-to-use drag-n-drop Photoshop scene creator with more than 2800 items.

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