// SDR# plug-in usercontrol ....

           private Control _fftControl = null;
            try
            {
                foreach (Control ctrl in this.ParentForm.Controls)
                {
                    if (ctrl.Name.Equals("centerPanel"))
                    {
                        _fftControl = ctrl;
                        break;
                    }
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }

            Bitmap bitmap = new Bitmap(_fftControl.Width, _fftControl.Height);
            _fftControl.DrawToBitmap(bitmap, new Rectangle(0, 0, _fftControl.Width, _fftControl.Height));