CleanIfTransparent

public static long CleanIfTransparent(Bitmap bmp)
        {
            long rtn = 0;
            //does our image contain an alpha channel?
            if ((bmp.Flags & 0x2) != 0 && bmp.PixelFormat == PixelFormat.Format32bppArgb)
            {
                //get int pointer to bmp.
                BitmapData bData = bmp.LockBits(
                    new Rectangle(0, 0, bmp.Width, bmp.Height),
                    ImageLockMode.ReadOnly,
                    PixelFormat.Format32bppArgb);
                IntPtr iptr = bData.Scan0;

                //get byteCount of bmp.
                int len = bmp.Height * Math.Abs(bData.Stride) / 4;

                unsafe
                {
                    //get pointer from intpointer
                    byte* ptr = (byte*)iptr.ToPointer();
                    //loop through image.
                    for (int i = 0; i < len; i++)
                    {
                        //the pixel value in bgra
                        //inverse alpha
                        byte a = (Byte)(0xFF - (*(ptr + 3)));
                        //do we have a value for our alpha?
                        if (a > 0)
                        {
                            rtn++;
                            //blue
                            *ptr = (byte)(Math.Min(*ptr + a, 255));
                            ptr++;
                            //green
                            *ptr = (byte)(Math.Min(*ptr + a, 255));
                            ptr++;
                            //red
                            *ptr = (byte)(Math.Min(*ptr + a, 255));
                            ptr++;
                            //alpha
                            *ptr = 0xFF;
                        }
                        else
                        {
                            ptr = ptr + 3;
                        }

                        if (i < len - 1)
                        {
                            ptr++;
                        }
                    }
                }
                bmp.UnlockBits(bData);
            }
            return rtn;
        }