In Gimp there are a wide variety of tools at the user’s disposal for colouring an area. Here we are going to learn how to use the gradient tool to selectively colour an area, in this case the iris of an eye, and to make the colour appear more a part of the image than if we dropped the colour straight into the image and left it.
Step 1 Our first action will be to duplicate the background layer so that we can create a selection of just the Iris and modify that part of the image without affecting the rest of the picture. To isolate the Iris draw a path around it using the Path tool.
Step 2 With our path in place use Select>From Path to turn it into a selection, then use Select>Feather to soften the edges of the selection.
Step 3 Now use the Magic Wand to select the pupil, then feather the selection and delete this area too. You should be left with a layer consisting only of the iris now, though the rest of the image will still be visible due to the background layer. You can check whether you successfully did this by clicking on the eye icon next to the background layer to hide it, and again to bring it back. If you have removed the right areas you should be presented with something like this screenshot when you hide the background.
Step 4 Desaturate the iris using Colours>Desaturate and select average. Now your Irish is ready for colouring.
Step 5 Create a new layer and name it ‘Colour’, then change the layer mode to Overlay.
Step 6 Select the Gradient tool and in the lower left-hand pane change the Shape to Conical and change the Gradient to the ‘Full Saturation Spectrum CW’ which looks like a rainbow. Now click and hold the left mouse button in the centre of the pupil and drag across before releasing it. Your layer will now be filled with the gradient.
Step 7 Now use the Magic Wand tool in the layer containing the iris to select both the pupil and the outside of the eye and feather the selection before switching to the gradient layer and pressing delete to remove the colours that would cover the rest of the image.
Step 8 Now you may have some bits that were not fully selected due to us using the Magic Wand to select, so go into the gradient layer with a soft-edged Eraser and remove any areas that are overlapping the white of the eye or the iris.
Step 9 Now we shall make the gradient less intense so it appears to be a more integral part of the image. First, use the opacity setting in the ‘Colour’ layer to reduce the vividness of the colour and allowing more of the eye’s detail to show through. Then use a soft-edged eraser set to around 30% opacity to fade the edges of the gradient next to the white of the eye.
There you have it, a selectively coloured eye using the gradient tool, try using the various gradient settings to create different effects; most of them use the foreground and background colours you have selected, so the possibilities are almost endless.