/// <summary>
/// Gets a transparent bitmap given two non-transparent bitmaps drawn against a white and black background respectively.
/// </summary>
/// <param name="whiteBmp">A non-transparent bitmap drawn against a white background.</param>
/// <param name="blackBmp">A non-transparent bitmap drawn against a black background.</param>
/// <returns>A 32-bit bitmap with an alpha channel values that are set based on white and black bitmap interpolation.</returns>
/// <exception cref="ArgumentException">Bitmaps must be of the same size and their pixel format must be Format32bppArgb.</exception>
public static Bitmap GetTransparentBitmap(Bitmap whiteBmp, Bitmap blackBmp)
{
if (whiteBmp.Size != blackBmp.Size && whiteBmp.PixelFormat != blackBmp.PixelFormat && whiteBmp.PixelFormat != PixelFormat.Format32bppArgb)
{
throw new ArgumentException("Bitmaps must be of the same size and their pixel format must be Format32bppArgb.");
}
var bmp = new Bitmap(whiteBmp.Width, whiteBmp.Height, whiteBmp.PixelFormat);
using (SmartBitmapLock oVals = new SmartBitmapLock(bmp), wVals = new SmartBitmapLock(whiteBmp), bVals = new SmartBitmapLock(blackBmp))
{
for (var i = 0; i < oVals.Length; i++)
{
Color b = bVals[i], w = wVals[i];
if (w == Color.White && b == Color.Black)
{
oVals[i] = Color.FromArgb(0);
}
else if (w != b)
{
double oc, op;
if (b == Color.Black)
{
oVals[i] = Color.FromArgb(255 - w.R, 0, 0, 0);
continue;
}
if (w.R != b.R && b.R != 0)
{
oc = CalcOrigColor(w.R, b.R);
op = b.R / oc;
}
else if (w.G != b.G && b.G != 0)
{
oc = CalcOrigColor(w.G, b.G);
op = b.G / oc;
}
else
{
oc = CalcOrigColor(w.B, b.B);
op = b.B / oc;
}
oVals[i] =
Color.FromArgb(RoundBound(op * 255.0), RoundBound(b.R / op), RoundBound(b.G / op), RoundBound(b.B / op));
}
else
{
oVals[i] = bVals[i];
}
}
}
return(bmp);
int RoundBound(double v) => (int)Math.Round(Math.Min(255.0, Math.Max(0.0, v)));
double CalcOrigColor(byte w, byte b) => 255.0 * b / (255.0 - w + b);
}
public void Dispose()
{
bmpLock = null;
}
internal Enumertor(SmartBitmapLock bmp)
{
bmpLock = bmp;
}
