Quite a while back I wrote about a technique to invert your images from negatives to positives or vice versa that involved an Adobe Camera Raw workaround. In looking at my blog stats, I notice that people are still reading that post, so I thought I would provide an easier technique — now that Lightroom 3 has a point curve, you can invert your images directly.
In the Tone Curve panel of the Develop module click on the point curve icon to switch to the point curve:
In the drop-down next to the point curve icon, choose Linear. This will remove all points from the curve:
Now take the point at the top right corner of the curve and pull it all the way down to the bottom of the chart. (It may fight you — it helps to pull it part way, let go, then pull it further.) Then take the bottom left corner point and pull it all the way up:
That’s it! If you accidentally end up with extra points on your curve, click and drag them all the way off the chart, or switch the drop down back to Linear and start over.
If you plan to invert many images, save this tone curve as a preset: click on the + at the top of the Presets panel on the left, give it a name (“Invert”) and check only Tone Curve. Next time you want to invert an image, just click on the Invert preset in your User Presets folder.