P: Tone curve broken...White point not adjustable

Greetings all,

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@Rikk Flohr: Photography @Bob Somrak 

I believe LrC is simply constantly using ExtendedToneCurvePV2012 and the ExtenedRGB while ACR is not.

Please notice that as soon as we engage HDREditMode even ACR behaves like LrC

ACR in SDR

When in HDREditMode 

All signs point out at LrC using ExtendedToneCurvePV2012 at all times even in SDR 

I had observed this behavior time ago internally and was never given an answer.

One control points are created in the HDR region and we switch to SDR then ACR as well will keep using ExtendedToneCurvePV2012 and the ExtenedRGB to not break the curve just like LrC does.

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@richardplondon 

I don't know how this change in behavior affects "existing" edits with the old behavior as I do not think I have ever done this on one of my photos except in testing.  If it does it would require a new process version.  Also, the fact that it only affects the white point and not the black point indicates it is a bug introduced when the histogram was changed to accomodate HDR.

Is a departure from the established norm, always a BUG? Could be the first showing of a functional redesign - OR could be a simple failure to remain the same. Curious minds wonder which!

Is the illustration below an accurate representation of the problem? Because if I look at this as a movement restriction (can’t move the white point along two axes simultaneously), I don’t see any evidence of that, because there are many times in the uploaded videos where both the white point input and output values change in the next frame as the white point is dragged.

But what I did notice is what happens to the point curve beyond the white point, when the white point Input and Output values are both lowered. Is that what you mean? If so, I do see that: What Lightroom Classic does with the point curve beyond the white point is not consistent with what Photoshop and Camera Raw do. In the Lightroom Classic example below, the green highlight is what other Adobe software do, but the red highlight is what Lightroom Classic does. Which is a little weird, because it seems like because Camera Raw and Lightroom Classic process the same way, at least those two should match, if not all three.

It seems that two points define a straight line (tilting as you move the points around).

Three or more points define a spline curve (which bends around as you move the points).

If you want to bring down some parts of the histogram while bringing up other parts of the histogram, a straight line logically and geometrically can't do this. It requires a midpoints curve defined by (at minimum) three points.

So that involves clicking in between the point defining white, and the point defining black, to place a new point that can then tonally "shape" things.

The illustrated behaviour from PS is in effect producing three points with a sharp corner between, and in the process is forcing a very distinct and sudden clip. A curve transition for this "bend" is much more pictorially benign IMO. It's important to remember that PS and LrC constitute very different kinds of postprocessing "space" with different design aims and practical usages. As I consider it, if PS and LrC did operate exactly the same way as each other, our available toolkiit would be poorer not richer for that. Perhaps LrC tone curve points did previously work as those in PS still do - I don't remember - but the current behaviour in LrC seems to be workable. Life is change!

I am not able to replicate this problem. The White Point of the Curve (Point, R, G, or B) moves in both directions simultaneously. 

I recommend resetting your preference file to see if it clears the bad behavior. 

This procedure works for both Lightroom Classic and Lightroom Desktop.

If you are using Lightroom Desktop, it can change your local storage location. Please review this setting after resetting preferences. 

Reset Procedure:

1. Close Lightroom.

2. Hold down [Alt/Opt]+[Shift] while restarting Lightroom.

3. Overwrite the Preferences when prompted by the dialog.

4. Close Lightroom.

5. Restart Lightroom.