The Gradient Editor

The Gradient Editor is used with both the Gradient Tool and the Gradient Map adjustment layer. In each of these facilities there is the possibility of mapping to a range of colours. The gradient tool maps colour to position on the image in a variety of ways and the gradient map adjustment layer maps colour to the variations in luminosity of the image. See the Gradient Tool and Gradient Map notes for more information.

Note that luminosity and brightness are related but not the same. Brightness is a purely numerical measure. It is the value associated with the brightest value of the red green and blue values expressed as a percentage of 255. Luminosity is a subjective measure. It allows for the fact that blue always appears darker than red and red appears darker than green. The contributions from each colour are added.

Above the gradient editor showing the various components of the dialog box.

The main object of interest is the coloured band across the lower third of the box. The rest of the components are there to enable this coloured band to be defined.

The colour of the band is determined by a set of stops as shown in Figure 1. The colour of the stops can be changed using the colour picker (see the colour picker note).

Stops

When two or more of the stops under the colour band have been allocated different colours the program forms a graded blend of colours between each pair of stops.

When a stop is selected by clicking on it, its colour can be changed by bringing up the colour picker either by double clicking on the stop or clicking on the coloured patch labelled Colour.

New stops can be added by clicking in the space between stops.

By default blending is achieved by reducing one colour and increasing the other in proportion to the distance between the stops. If one stop is a red say (200,0,0) and the other a green say (0,100,0) then half way between these stops will be (100,50,0) i.e. half the red and half the green. The colour mid points described below can be used to alter the way blending occurs. The mean value need not occur at the halfway point between two stops.

If one or both of the outer stops are not at an end of the coloured band then the outer colour will persist unchanged to the end of the band.

The stops can be moved either by dragging them or adjusting the values in the location text box.

To remove a stop, select it and then click on the Delete button.

NOTE When trying to select either a stop or a mid point, it is difficult to avoid occasionally creating a new stop by clicking in the space so delete is very useful.

Colour Mid Points

When a stop is selected by clicking on it, small diamonds (labelled Colour Mid Points in Figure 1) appears between it and adjacent stops. These colour mid points indicate the middle of the blend between the two adjacent stops. (The effect of moving them is a bit like moving the middle slider in levels. It is akin to adjusting the gamma.) So if as above one stop is a red (200,0,0) and the other a green (0,100,0) and the diamond between them is moved to only one quarter of the way from the red to the green then this point will have the colour (100,50,0) and the rest of the colours will be adjusted accordingly. Try setting up some coloured stops and see the effect of moving the mid points.

Preset Colours

To use the preset colours that appear in squares at the top of the dialog box just click on the required one and it will be tansferred to the coloured band. Most of the presets contain fixed colours. The first two and the last one take their colours from the chosen foreground and background colours in the tools pallet.

The first preset simply maps from the foreground to the background colour whereas the second one maps from the foreground colour to transparent. The last one map a series of foreground stripes and transparent (lack?) of stripes. (Note Transparency or opacity is only supported by the gradient tool. The gradient map adjustment layer will fill transparent bits with the adjacent colour.) All presets can be edited by adding stops or changing the colours.

Opacity Stops

The stops on the upper side of the colour band control opacity.

Note; There is a confusion of notation between opacity and transparency. In the gradient editor the action of the upper stops is referred to as “opacity”. In the gradient tool bar the action of these stops is turned on an off by a check box labelled “Transparency” and the overall opacity of the gradient tool as it paints is controlled by a slider labelled “Opacity”.

Using the opacity stops is similar to using the colour stops. Click on a stop and the opacity can be changed by setting a value in the opacity text box. Either type in a value or use the slider.

In addition the position of the stop can be changed either by dragging it along or adjusting the values in the location text box.

Gradient Type and Smoothness

In order to move the stops and determine the colours it is necessary to select the Solid gradient type. The alternative is random. Random certainly does produce some unusual effects but as its results are random it is for playing at being artistic.

More

Click on the more button and a drop down list of options appear. Different sets of preset gradients can be chosen and the display of the presets can be changed.

New Name Load and Save

These remaining options allow the creation naming and saving of custom gradients in the usual way. The saved gradients can be loaded as required.