10. Gradients

10. Gradients
	第 7 章用 GIMP 绘画

图 7.22. Some examples of GIMP gradients.

Gradients from top to bottom: FG to BG (RGB); Full saturation spectrum; Nauseating headache; Browns; Four bars

A gradient is a set of colors arranged in a linear order. The most basic use of gradients is by the Gradient tool, sometimes known as “gradient fill tool”: it works by filling the selection with colors from a gradient. You have many options to choose from for controlling the way the gradient colors are arranged within the selection. There are also other important ways to use gradients, including:

用渐变绘画: GIMP的每个基本绘画工具都允许您选择使用渐变颜色。这使您能够创建从一端到另一端改变颜色的笔触。
渐变映射滤镜: This filter is in the Colors menu, and allows you to “colorize” an image, using the color intensity of each point with the corresponding color from the active gradient (the intensity 0, very dark, is replaced by the color at most left end of the gradient, progressively until the intensity is 255, very light, replaced by the most right color of the gradient. See 第 8.39 节 “Gradient Map” for more information.

当您安装GIMP时，它会预先提供大量有趣的渐变，您可以添加您创建或从其他来源下载的新渐变。您可以使用渐变对话框访问完整的可用渐变集，这是一个可停靠的对话框，您可以在需要时激活它，也可以将其作为选项卡保留在停靠栏中。在大多数与渐变相关的操作中，使用的“当前渐变”显示在工具箱的笔刷/图案/渐变区域中。单击工具箱中的渐变符号是打开渐变对话框的另一种方法。

许多使用渐变的快速示例（有关更多信息，请参阅渐变工具）：

将渐变放置在选区中：
1. 选择一个渐变。
2. 在选区的两个点之间使用鼠标单击并拖动混合工具。
3. 颜色将垂直于鼠标拖动的方向并根据拖动的长度分布。
图 7.23. 如何在选区中快速使用渐变
用渐变绘画：

You can also use a gradient with one of the drawing tools (e.g. Pencil, Paintbrush or Airbrush) if you switch on Enable dynamics and set Dynamics to Color From Gradient. In the next step, set the gradients length and the Repeat style in the Fade Options section, and select a suitable gradient in the Color Options section. 第 3.2.6 节 “Dynamics Options” describes these parameters in more detail.

The following example shows the impact on the Pencil tool.

图 7.24. How to use a gradient with a drawing tool

Tool settings

Resulting succession of the gradients colors
具有相同渐变的不同产物：

图 7.25. 渐变用法

使用Tropical Colors渐变的四种方法：线性渐变填充，成形渐变填充，使用渐变颜色绘制的笔触，以及使用模糊笔刷绘制、然后使用渐变映射滤镜着色的笔触。

关于GIMP渐变的一些有用信息：

The first gradients in the list are special: They use the colors from the Foreground/Background Colors Area in the Toolbox, instead of being fixed.
- FG to BG (HSV Counter-Clockwise) represents the hue succession in a color wheel from the selected hue to 360°.
- FG to BG (HSV Clockwise) represents the hue succession in a color wheel from the selected hue to 0°.
- FG to BG (RGB) is the RGB representation of the gradient from the Foreground color to the Background color in Toolbox.
- FG to BG (Hard Edge)
- With FG to Transparent, the selected hue becomes more and more transparent. You can modify these colors by using the Color Selector. Thus, by altering the foreground and background colors, you can make these gradients transition smoothly between any two colors you want.
- FG to Transparent (Hard Edge)
渐变不仅涉及颜色变化，还涉及不透明度的变化。有些渐变是完全不透明的；其他包括透明或半透明部分。当您使用非不透明渐变填充或绘制时，图层的现有内容将在其后面显示出来。
您可以使用渐变编辑器创建新的自定义渐变。您不能修改随GIMP提供的渐变，但您可以复制它们或创建新的渐变，然后编辑它们。

GIMP提供的渐变存储在系统gradients文件夹中。默认情况下，您创建的渐变存储在您的私人GIMP目录中的gradients文件夹中。在这些文件夹之一中找到的任何渐变文件（以扩展名.ggr结尾），将在您启动GIMP时自动加载。如果需要，您可以在首选项对话框的数据文件夹页面的渐变选项卡中，向渐变搜索路径添加更多文件夹。

GIMP can also load gradient files in SVG format, used by many vector graphics programs. To make GIMP load an SVG gradient file, all you need to do is place it in the gradients folder of your personal GIMP directory, or any other folder in your gradient search path.

	提示
	您可以在网络上找到大量有趣的 SVG 渐变，特别是在 OpenClipArt 渐变 [OPENCLIPART-GRADIENT]。除非您的浏览器支持 SVG，否则您将无法看到这些渐变的外观，但这不会阻止您下载它们。