'半透明合成する
For i = 0 To UBound(pix1)
    '色を分解
    r = GetRed(pix1(i))
    g = GetGreen(pix1(i))
    b = GetBlue(pix1(i))
    r2 = GetRed(pix2(i))
    g2 = GetGreen(pix2(i))
    b2 = GetBlue(pix2(i))
    
    '半透明化
    r = (r + r2) \ 2
    g = (g + g2) \ 2
    b = (b + b2) \ 2
    
    '色をセット
    pix1(i) = RGB(r, g, b)
Next i