The Gradient Map

The gradient map adjustment layer maps luminosity of an image to a selection of colours. The colours used in the mapping can be selected in the gradient editor which is described in a separate note.

The gradient map can be accessed by selecting Layer-New Adjustment Layer-Gradient map in which case a dialog box will appear that allows the layer to be named, the transparency to be set, the blending mode to be set and also allows the new layer to be grouped with the previous layer. All of these can be set later so can simply be ignored by pressing OK.

Alternatively a Gradient Map can be created by clicking on the half moon symbol in the layers pallet and selecting the Gradient Map.

Either action will create a new Gradient Map adjustment layer.

The following dialog box will appear.

At this point there are a number of simple choices.

The preview tick box allows an immediate application of the gradient to the main image.

Click on the coloured band representing the current gradient and the Gradient Editor will be displayed. The use of the gradient editor is described in more detail in the note called Gradient Editor.

Reverse applies the gradient as if it were back to front. Note that the gradient shown in this box will reverse but on entering the gradient editor (see below) the displayed gradient will be the original way round.

Dither is a method of rendering the colours in such a way as to avoid certain types of banding. For a more detailed comment see the not on the Gradient Tool.

The small box I’ve labelled “Brings up the current preset gradients” is a short cut that allows selection from the current presets but does not allow any other editing. It can be ignored at this stage as the Gradient Editor allows the choice of preset gradient.

Uses

One of the most obvious uses for the gradient map is to map the luminosity to black and white creating a black and white image.

Display an image that you require to be black and white and create a Gradient Map adjustment layer. Access the gradient editor from the gradient map dialog box then choose the black to white gradient (the third from the left in the default set of preset gradients). If preview is set then the image will immediately change to a black and white image.

The mapping is such that the left hand side of the gradient map, maps to the least luminous parts of the image. The right hand side maps to the most luminous parts of the image.

Note if the reverse box is ticked then the mapping will be reversed and the gradient shown in the New Layer box will be reversed but the gradient shown in the editor will be the original way round.

Any gradient that can be produced will act as a mapping from luminosity to the chosen colours.

Subtle tints to violent lurid effects can be produced.