两个RGB的颜色半透明混色算法 (2007-07-19)

发布时间 2007-07-19 13:45:00

各点像素的RGB值是按一定比例混合而成的，这个比例由Alpha值决定，具体算式见下：

Alpha = 0 ~ 100
R = ( R1 * (100 - Alpha) + R2 * Alpha ) / 100
G = ( G1 * (100 - Alpha) + G2 * Alpha ) / 100
B = ( B1 * (100 - Alpha) + B2 * Alpha ) / 100

示例：
RGB1 ( 232, 54, 13 )
RGB2 ( 94, 186, 233 )

Alpha = 30
R = ( 232 * 70 + 94 * 30 ) / 100 = 190.6 -> 190
G = ( 54 * 70 + 186 * 30 ) / 100 = 93.6 -> 93
B = ( 13 * 70 + 233 * 30 ) / 100 = 79

Alpha = 50
R = ( 232 * 50 + 94 * 50 ) / 100 = 163
G = ( 54 * 50 + 186 * 50 ) / 100 = 120
B = ( 13 * 50 + 233 * 50 ) / 100 = 123

这样在Java中可以对以上计算方法封装成函数或类，以方便代码复用，对应的Java代码如下：

protected Color calculateAlphaValue(Color c1, Color c2, int alpha)
{
  if (alpha < MIN_ALPHA)
  alpha = MIN_ALPHA;
  else if (alpha > MAX_ALPHA)
  alpha = MAX_ALPHA;
 
  int R = (c1.getRed() * (MAX_ALPHA - alpha) + c2.getRed() * alpha) / MAX_ALPHA;
  int G = (c1.getGreen() * (MAX_ALPHA - alpha) + c2.getGreen() * alpha) / MAX_ALPHA;
  int B = (c1.getBlue() * (MAX_ALPHA - alpha) + c2.getBlue() * alpha) / MAX_ALPHA;
 
  return new Color(R, G, B);
}

32位色下的颜色混合

R = R1 * Alpha1 + R2 * Alpha2 * (1-Alpha1)
G = G1 * Alpha1 + G2 * Alpha2 * (1-Alpha1)
B = B1 * Alpha1 + B2 * Alpha2 * (1-Alpha1)
Alpha = 1 - (1 - Alpha1) * ( 1 - Alpha2)
R = R / Alpha
G = G / Alpha
B = B / Alpha