Toning
Used as a way of colouring and preserving photographs sepia toning gives a distinctive look. The methods of replacing the silver in a black and white print with a warm tone can be reproduced digitally.
Many colours can also be applied using gradients. The GIMP has a filter buried away in its menus that tones a photograph based on its luminance.
Sepia toning
The images in this gallery were created using Eric R. Jeschke's GIMP.org tutorial.
This technique uses a layer mask to selectively apply a colour or gradient to the tones in a photograph.
Gradient maps
A simple method for applying a gradient uses the GIMP gradient map filter.
Select: Filters -> Colours -> Map -> Gradient Map from the image menu.
The filter applies a chosen gradient across the tonal range of the image. The left hand side of the gradient is mapped to the darkest and right to the lightest calculated pixel.
The gradients chosen for the gallery are subdived into types to show the effects they have on different types of photographs.