Lightroom tip: advanced custom curves

English Wine & Beer Shop, India, August 2008

Lightroom 2.0, Windows XP
Read my tips intro if you're new.

How do I create my own curve profiles?

I previously posted on setting a Lightroom preset to do a basic tone curve inversion. You'll need to understand that, before reading on. I then wanted to go further, introducing my own custom curves, especially for my 35mm black and white scans.

I always scan my black and white as a positive and then invert in software. For a good explanation why you'd ever want to do this, read the post Matt Alofs wrote on the subject. When a negative is scanned as positive it usually compresses all the tones into the lower half of the spectrum, so on inversion it all ends up at the top. For me, the original positive scan rarely goes to more than 128 on a 255 scale (of course I'm scanning to 16 bit output files, not 8 bit).

After inversion, the first thing I want to do is apply a levels adjustment to bring the shadows back down into the lower tones. That meant a trip to Photoshop after importing into Lightroom to get a levels adjustment. I can, in fact, combine the 2 into one Lightroom preset. Here's how. The key is to set the "black point" of the inversion to a different point, close to the maximum scan value. So, instead of my black point origin being at 255,0, I want it at 130,0 so that the maximum scan value of 128 is just above the black point (so I can tweak later).

Here's what the preset file looks like with the change.

s = {
id = "498D92B2-EB89-4054-AAA2-46D3207AB652",
internalName = "Tone test",
title = "Invert 2",
type = "Develop",
value = {
settings = {
ConvertToGrayscale = false,
EnableGrayscaleMix = true,
ParametricDarks = 0,
ParametricHighlightSplit = 75,
ParametricHighlights = 0,
ParametricLights = 0,
ParametricMidtoneSplit = 50,
ParametricShadowSplit = 25,
ParametricShadows = 0,
ToneCurve = {
0,
255,
130,
0,
},
ToneCurveName = "Linear",
},
uuid = "8422BC3B-D8AA-4981-9F69-C350D56D935E",
},
version = 0,
}

I can now import into Lightroom applying the preset to the entire batch and get pretty good results from the off. This minimises the amount of work I need to do in other software. Of course, results may vary with film, scanner and exposure technique, so you might need to tweak the values for you own set-up.

If you're not good at reading negatives (and thus scan everything to check the best ones) this should speed things up considerably for you.

But there's more. What if I want a custom conversion curve to cover standard contrast or gamma adjustments? Well that can also be done (for positive or negative), by including extra points into the ToneCurve section of the preference. Here's a (rather stupid) example:

s = { id = "498D92B2-EB89-4054-AAA2-46D3207AB652", internalName = "Tone test", title = "Curve weird", type = "Develop", value = { settings = { ConvertToGrayscale = false, EnableGrayscaleMix = true, ParametricDarks = 0, ParametricHighlightSplit = 0, ParametricHighlights = 0, ParametricLights = 0, ParametricMidtoneSplit = 0, ParametricShadowSplit = 0, ParametricShadows = 0, ToneCurve = { 0, 0, 32, 130, 65, 100, 97, 60, 255, 255, }, ToneCurveName = "Linear", }, uuid = "8422BC3B-D8AA-4981-9F69-C350D56D935E", }, version = 0, }

The same shot as above with the strange curve applied

In fact, Lightroom curves can take any number of arbitrary x,y points to define the curve, you just have to open a text editor to get at the function.

So now, if you can translate multiple curve effects into a single curve they can be applied in Lightroom. A bit fiddly, but possible. Once the technique is known, the possibilities are endless.

Rather begs the question, if this ability exists in the software, why not expose it in the GUI?