确定通过组合两种颜色接收的RGBA颜色 [英] Determine RGBA colour received by combining two colours

问题描述

我有两种颜色定义为RGBA（在我的具体例子中，其中一个集合是[白色与alpha 0.85]和[57,40,28与alpha 0.25]。第二个颜色绘制在第一个白色与阿尔法是背景，第二种颜色是用于绘图）。我怎么知道什么是RGBA颜色的组合是什么？我需要做一次性 - 所以任何工具都很好（例如我

I have two colours defined as RGBA (in my specific examples, one of the set is [white with alpha 0.85] and [57, 40, 28 with alpha 0.25]. The second colour is drawn over the first one (i.e. white with alpha is the background and the second colour is used for drawing). How can I figure out what the RGBA colour of the combination is going to be? I need to do this one-off - so any tools is fine (e.g. I'm happy to draw something in photoshop and see what comes out).

我有几组合并，但不是太多任何指针？谢谢。

I have several sets to combine, but not too many. Any pointers? Thanks.

推荐答案

使用画家算法< a>最常用的颜色合成是使用 Porter-Duff 过模式完成的：

结果alpha：

αr = αa + αb (1 - αa)

结果颜色组件：

Cr = (Ca αa + Cb αb (1 - αa)) / αr

您的示例：

So for your example:

alpha = 0.25 + 0.85 * (1 - 0.25)                        = 0.8875

red   = (57 * 0.25 + 255 * 0.85 * (1 - 0.25)) / 0.8875  = 199.2
green = (40 * 0.25 + 255 * 0.85 * (1 - 0.25)) / 0.8875  = 194.4
blue  = (28 * 0.25 + 255 * 0.85 * (1 - 0.25)) / 0.8875  = 191.1

关于Alpha合成的维基百科文章。

See wikipedia article on alpha compositing.

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