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Grokking The Gimp
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8.2 Gradient Rendering Techniques

In Section  4.3.3, gradients were discussed as tools for making masks. However, they are also very useful for rendering.

Figure  8.4

  
Figure 8.4: The Different Gradient Types
Figure 8.4

shows the Tool Options dialog for the Gradient tool. As shown in the Blend menu, there are a total of 11 different gradient types. The Conical (symmetric),   Shapeburst,   and Bi-Linear   options are of particular interest for rendering effects.

Figure  8.5

  
Figure 8.5: Examples of Conical, Bi-Linear, and Shapeburst Gradients
Figure 8.5

illustrates examples of conical, bi-linear, and shapeburst gradients. As shown in Figure  8.5(a), conical gradients produce a dimpled effect. As illustrated in Figure  8.5(b), bi-linear gradients create the illusion of the specular sheen that would be created from a metallic or glassy cylindrical surface. As displayed in Figure  8.5(c), shapeburst gradients produce a beveled effect. Thus, each of these gradients produces an illusion of a 3D surface.

As an example of using a gradient to render a 3D effect, a beveled look is created for some text using a shapeburst gradient. Figure  8.6(a)

  
Figure 8.6: Creating Text to be Used in Gradient Rendering Example
Figure 8.6

displays the text, created using the Baltar font at a height of 175 pixels. This is a thick, blocky type that is perfect for a bevel effect. The Layers dialog, displayed in Figure  8.6(b), shows that the image consists of three layers. There is the white background and a transparent layer, both which were created before invoking the Text tool, and a floating selection containing the text. The floating selection is created automatically by the Text tool and must be anchored before being able to work on other layers in the image.

Before anchoring, however, the text is centered.   This is accomplished by typing C-x and then C-v in the image window. This trick cuts and then re-pastes the floating selection, perfectly centered in the window. After the floating selection is anchored into the transparent layer below it, the text is selected using the Alpha to Selection  function found in the Layers menu. The selected text can be seen in Figure  8.6(a).

Figure  8.7(a)

  
Figure 8.7: Rendering a Beveled Look
Figure 8.7

shows the application of a gradient to the selected text (note that for clarity the visibility of the Marching Ants has been toggled off). Figure  8.7(b) shows that the Shapeburst (angular) gradient has been chosen, and Figure  8.7(a) displays the resulting beveled effect that this creates with the text.

Normally, gradients are applied to images by clicking and dragging in the image window. The two points defined by where the mouse was clicked and where it was released specify the orientation and the extent of the applied gradient. The curious thing about Shapeburst gradients, however, is that the result does not depend on where the mouse is clicked, nor on where it is released. It just fills the active region with a shapeburst, regardless of how the mouse is used.

The way in which a shapeburst gradient transitions from the foreground to background color can be controlled by the type of shapeburst. As shown in Figure  8.4, there are three different shapeburst types: angular, spherical, and dimpled. Shapeburst (spherical) produces the roundest bevel and Shapeburst (dimpled) the sharpest. Shapeburst (angular) is a compromise between the two.

The result in Figure  8.7 can be made to look a lot jazzier by applying another shapeburst gradient to the Background layer. The result of applying the Shapeburst (spherical) gradient to the Background layer is shown in Figure  8.8(a).

  
Figure 8.8: The Beveled Text on a Rendered Background
Figure 8.8

The gradient's foreground color is red and the background color is black. Figure  8.8(b) shows the corresponding Layers dialog.




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