GDI的混合公式+

Question

我有一个颜色A，我想通过使用颜色B转换成C颜色。所以我想知道GDI +中的混合公式F，其中F = F（A，B ）= C. A是 “底色”，而B是一个覆盖颜色上述A，其与A一起产生C.

干杯，

//马格努斯

Answer 1

这被称为Alpha Blending。

使用以下算法用于R，G和B分量，其中alpha是0和1之间

newColor = MAX(255, (1 - alpha) * background + alpha * overlay) 

Answer 2

基本上（α，红，绿，蓝以0至1的范围）：

Result.Alpha = BackColor.Alpha + ForeColor.Alpha - （BackColor.Alpha * ForeColor.Alpha）
Result.Red =（（ForeColor.Red * ForeColor.Alpha）+（BackColor.Red * BackColor.Alpha *（1 - ForeColor.Alpha）））/ Result.Alpha
（将'red'替换为'green'和'blue'以获得corr esponding函数）

对于32位颜色，在VB.NET（有点优化）：

Shared Function Flatten(ByVal BackColor As Color, ByVal ForeColor As Color) As Color 
    If ForeColor.A = 0 Then Return BackColor ' Prevent division by zero 
    If ForeColor.A = 255 Then Return ForeColor ' Shortcut 

    Dim BackAlphaDbl As Single = CSng(BackColor.A) ' Convert to single to prevent in-calculation 8 bit overflow 
    Dim ForeAlphaDbl As Single = CSng(ForeColor.A) 

    Dim ForeAlphaNormalized As Single = ForeAlphaDbl/255 ' Precalculate for triple use 
    Dim BackcolorMultiplier As Single = BackAlphaDbl * (1 - ForeAlphaNormalized) ' Precalculate 

    Dim Alpha As Single = BackAlphaDbl + ForeAlphaDbl - BackAlphaDbl * ForeAlphaNormalized 

    Return Color.FromArgb(Alpha, (ForeColor.R * ForeAlphaDbl + BackColor.R * BackcolorMultiplier)/Alpha, (ForeColor.G * ForeAlphaDbl + BackColor.G * BackcolorMultiplier)/Alpha, (ForeColor.B * ForeAlphaDbl + BackColor.B * BackcolorMultiplier)/Alpha) 
End Function 

我用纸和笔这出，并通过与GDI重叠图像+和测试所得颜色验证它。这个函数和GDI +的唯一区别在于GDI +在前景阿尔法变化时上下不一致。这个功能更精确。