Lightroom tip: invert tone curve

Lightroom 2.0, Windows XP.
read my tips intro first.

How do I invert the tone curve?

I've seen a few utilities available online and a lot of questions on how to, but nowhere that showed you how. So here it is. I'm assuming you know how to create a development preset.

First you need to know a bit more about Lightroom presets. They work as formatted text files, which makes them very editable. In Windows XP they're stored at: C:\Documents and Settings\%username%\Application Data\Adobe\Lightroom regardless of software install directory (for example, I've got Lightroom installed on the G:\ drive). For this you'll need to get into the \Develop Presets\User Presets sub-folder.

But first, it's easiest to create a blank tone curve and save as preset, with a name you can remember (easier than editing from scratch). If, for eample, you created a preset called invert, go to the prest directory and open invert.lrtemplate. The text should look like this:

s = {
id = "498D92B2-EB89-4054-AAA2-46D3207AB652",
internalName = "Tone test",
title = "Invert",
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,
250,
0,
},
ToneCurveName = "Linear",
},
uuid = "8422BC3B-D8AA-4981-9F69-C350D56D935E",
},
version = 0,
}

Note the line title, which is what shows up in the presets list in Lightroom. The important bit here, however, is the bit labelled ToneCurve. This lists the end points for the curve. We're going to reverse them from {0,0:255,255} to {0,255:255,0} thus:

ToneCurve = {
0,
255,
255,
0,
},

There it is, a basic straight line inversion curve for Adobe Lightroom. I actually do something a bit different, changing the black point instead, thus:

ToneCurve = {
0,
255,
250,
0,
},

I could also change the white point by setting the first pair to 0,250.

I'm going to come on to a fancier use of this in another post.