private void ClearBmp()
{
imgBit.LockBitmap(bmp);
for (int i = 0; i <= bmp.Width - 1; i++)
{
for (int j = 0; j <= bmp.Height - 1; j++)
{
imgBit.SetPixel(i, j, Color.Black);
}
}
imgBit.UnlockBitmap(bmp);
}