In this tutorial I'm going to show you how to split tone with Gradient Map in GIMP. If you're not familiar with the split tone technique, it is a way to add a color tint to a black and white digital photo, so that the shadows and highlights are tinted with different colors. This can produce some very subtle and unusual visual effects that lend more interest to a photo than a simple black and white conversion would.
The technique is inspired by the split tone effect that used to be achieved in film photography. In that case, the color tints were produced by processing films with non-specified chemicals that led to subtle color shifts in different tonal ranges of the photos. In the world of digital photography split tone effects can be much more varied with photographers able to select any mix of colors that they desire when processing their digital photos with this technique.
As with many creative effects that can be applied when processing your digital photos, there is more than one way to apply a split tone effect. Which you choose will be largely a matter of personal preference, but in the following steps I'll demonstrate how to split tone with Gradient Map in GIMP.
This technique is a bit more advanced than creating a split tone with Color Balance, which I've also covered, and you need to be able to create your own gradient using the Gradient Editor. However this technique offers you greater flexibility and you will be rewarded with greater control over the finished effect.