Tone Curve Background Color

There is no known way to change the colors in that area of the user interface.

But you might want to consider doing this another way. It sounds like you're trying to bring in the end points by looking at the graph alone. But that method can be flawed, because the tones at the exact ends of the histogram can include specular highlights and fully blocked shadows, which are often OK to cut off. But the graph cannot tell you what kind of tones are at the ends of the histogram, so you have to evaluate them by looking at the image itself. You can do this in Lightroom (and Photoshop and Camera Raw) by turning on the clipping display. When you have the clipping display on, you can visually inspect the image as you drag the end points in, so that you can make a more informed decision as to whether you should stop dragging where tones start appearing in the histogram, or keep going.

In other words, the flaw with looking at the histogram is that it doesn't tell you whether the end tones are important to the image, but the clipping display does. So if you properly use the clipping display, you kind of don't need to see the histogram at all when setting your end points. Which means you no longer need to care about the histogram colors.

For example, if part of the black film frame is in the scanned image area, those tones will appear at one end of the histogram but are not relevant to the content; if you clip where the histogram sees the black film frame tones start, you may be setting the black point incorrectly. But if you see that the black point starts clipping in the film frame instead of in the image, you immediately understand that it is OK to keep dragging until you see clipping in the image content itself.

By the way, the image used in the example is a scanned color negative, although I didn't show the inversion part because my scanning software does that.

LeviDavis49  wrote
I have worked the combined curve, but it does not give me as accurate of a rendition of the image like doing each R G B by themselves.
And as you can see distinguishing the edges can been formidable.  If I should brighten the color portion or white the background color, I would be able to see the edges much better.

What you are doing is the equivalent of PS's Auto Levels or Auto Curves function. This does two things with color negative film raw image files shot with a camera copier, 1) Removes the orange mask and 2) increases contrast.

A better way of doing this is to first apply only the single RGB Invert curve and use the WB Temp and Tint  controls or eyedropper on a neutral area to remove the orange mask. Then use the LR Tone controls to establish proper Exposure level, midtone Contrast and the White and Black points. Unfortunately ALL of the controls work backwards AND the Highlights, Shadows, Whites, and Blacks controls become nonlinear. The reason is they are working on the uninverted raw data backwards with the White and Black endpoints are reversed. These controls are designed to specifically recover highlights and shadow details, which require different raw data processing algorithms. Despite this backwards and non-linear behavior you can get fairly good rendering once you understand this behavior of the Tone controls with an inverted Tone curve.

The Lightroom WB Temp Control has limited range and with many color negative film emulsions the lowest 2000 Temp setting is not sufficient to fully remove the orange mask. Adobe DNG Editor can be used to extend the Temp range. I created four new Adobe Standard profiles using the Adobe DNG Profile Editor (DPE) with Temp and Tint -25 +25, -50 +50, -75 +75, and -100 +100. The Adobe camera profiles are dual-illuminant (Tungsten and Daylight). Use the DPE modified camera profile that keep the Temp setting at 5,000 or higher when the image is properly white balanced (i.e. neutral tones are neutral). The assumption here is of course that you used a daylight or flash when capturing the film image.

The DNG Profile Editor is a free software utility for creating or editing camera profiles.

Read more (PDF, 3.93 MB)
Download:  Mac, Win

You need to create a DNG copy of any raw file shot with the used to capture the negative film copies. Make sure the Base Profile is set to Adobe Standard. Use -Temp - and +Tint with equal values (-25 +25, -50 +50, -75 +75, -100 +100.

A better solution is for Adobe to provide an invert function that inverts the raw image data BEFORE any other controls are applied. The Tone controls will work then properly and the WB Temp and Tint controls should have adequate range without having to use DPE modified camera profiles. You can add your 'Me To' vote and 'Follow' at the below request for this capability.

Lightroom/Camera Raw: Ability to invert negative scans to positives (color and black-and-white) | Photoshop Family Custo…