GDI的混合公式+

Question

我有一個顏色A，我想通過使用顏色B轉換成C顏色。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是一個覆蓋顏色上述A，其與A一起產生C.

乾杯，

//馬格努斯

Answer 1

這被稱爲Alpha Blending。

使用以下算法用於R，G和B分量，其中alpha是0和1之間

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

Answer 2

基本上（α，紅，綠，藍以0至1的範圍）：

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
（將'red'替換爲'green'和'blue'以獲得corr esponding函數）

對於32位顏色，在VB.NET（有點優化）：

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 

我用紙和筆這出，並通過與GDI重疊圖像+和測試所得顏色驗證它。這個函數和GDI +的唯一區別在於GDI +在前景阿爾法變化時上下不一致。這個功能更精確。