C#+ArcEngine 自定义范围输出为栅格图像(JPG/BMP)

/// <summary>
        /// 打印输出.该功能目前测试只适用于JPEG,BMP.格式
        /// </summary>
        /// <param name="pExport"></param>
        /// <param name="dResolution">分辨率</param>
        /// <param name="outputPath">输出路径</param>
        /// <param name="pVisibleBounds">自定义可见区域</param>
        private void FunExportImage(IExport pExport, double dResolution, string outputPath,IEnvelope pVisibleBounds)
        {
            IEnvelope pPixelBounds;
            ESRI.ArcGIS.Display.tagRECT outtagRECT;
            ESRI.ArcGIS.Display.tagRECT DisplayBounds = m_ActiveView.ExportFrame;
            double iScreenResolution;
            if (pExport == null)
            {
                MessageBox.Show("打印类型未指定");
                return;
            }

            if(pVisibleBounds!=null) //自定义框范围
            {
                IDisplayTransformation pDisplayTransformation = m_ActiveView.ScreenDisplay.DisplayTransformation;
                pDisplayTransformation.TransformRect(pVisibleBounds, ref DisplayBounds, 8);//8代表esriDisplayTransformEnum.esriTransformToDevice
            }

            if (pExport is IExportImage)
            {
                IExportImage pExportImage = pExport as IExportImage;
                pExportImage.ImageType = esriExportImageType.esriExportImageTypeTrueColor;
            }

            iScreenResolution = m_ActiveView.ScreenDisplay.DisplayTransformation.Resolution;
                      
            double l_resolution = Convert.ToDouble(domainResolution.Value);

            //=====================================================================
            //
            //方法一
            //
            //一厘米包含37.79524个像素
            //double dPixel = 37.79524;
            ////按照设置输入分辨率计算一厘米所含的像素数
            //double tempratio = l_resolution * dPixel / iScreenResolution;
            ////输出图形的高度
            //double tempbottom = (DisplayBounds.bottom - DisplayBounds.top) * tempratio;
            ////输出图形的宽度
            //double tempright = (DisplayBounds.right - DisplayBounds.left) * tempratio + 0.1 * tempratio;
            //======================================================================
            //
            //方法二:暂时可行.
            //
            double tempratio = l_resolution / iScreenResolution;
            double tempbottom = (DisplayBounds.bottom - DisplayBounds.top) * tempratio;
            double tempright = (DisplayBounds.right - DisplayBounds.left) * tempratio;
            //=====================================================================
            outtagRECT.left = 0;
            outtagRECT.top = 0;
            outtagRECT.bottom = Convert.ToInt32(Math.Truncate(tempbottom));
            outtagRECT.right = Convert.ToInt32(Math.Truncate(tempright));

            pPixelBounds = new EnvelopeClass();
            pPixelBounds.PutCoords(outtagRECT.left, outtagRECT.top, outtagRECT.right, outtagRECT.bottom);

            pExport.Resolution = dResolution;
            pExport.PixelBounds = pPixelBounds;
            pExport.ExportFileName = outputPath;

            try
            {
                ITrackCancel pTrackCancel = new TrackCancelClass();
                int hDC;
                hDC = pExport.StartExporting();

                if (m_frmProBar == null) //m_frmProBar为进度条窗体
                    FunProgressBar();
                m_frmProBar.Show();

                m_ActiveView.Output(hDC, (int)dResolution, ref outtagRECT, pVisibleBounds, pTrackCancel);
                pExport.FinishExporting();

                m_frmProBar.Hide();

                if (DialogResult.Yes == MessageBox.Show("出图成功! \n图片保存在" + txtOutPutPath.Text+"\n是否需要打开文件所在的目录？", "提示", MessageBoxButtons.YesNo, MessageBoxIcon.Information))
                {
                    System.Diagnostics.Process.Start("explorer.exe", txtOutPutPath.Text); 
                }
                pExport.Cleanup();
            }
            catch
            {
                MessageBox.Show("出图失败!","警告",MessageBoxButtons.OK,MessageBoxIcon.Warning);
                //释放变量
                m_frmProBar = null;
                pExport = null;
                pVisibleBounds = null;
            }
            //释放变量
            pExport = null;
            pVisibleBounds = null;

        }