您可以使用以下代码:

Bitmap myBitmap = new Bitmap(@"YourPath");
const float limit = 0.3f;
for (int i = 0; i < myBitmap.Width; i++)
{
    for (int j = 0; j < myBitmap.Height; j++)
    {
        Color c = myBitmap.GetPixel(i, j);
        if (c.GetBrightness() > limit)
        {
            myBitmap.SetPixel(i, j, Color.White);
        }
    }
}
myBitmap.Save(@"YourNewPath");

并与limit一起玩以获得想要的东西.

And play with limit to get what you want.