导出图片，包含栅格的地图导出的图片模糊，arcgis eingine

原因：栅格数据重采样了，解决方法： 

            PixelBoundsEnv = new Envelope() as IEnvelope;

            if (bClipToGraphicsExtent && (docActiveView is IPageLayout))
            {
                docGraphicsExtentEnv = GetGraphicsExtent(docActiveView);
                docPageLayout = docActiveView as PageLayout;
                pUnitConvertor = new UnitConverter();

                //assign the x and y values representing the clipped area to the PixelBounds envelope
                PixelBoundsEnv.XMin = 0;
                PixelBoundsEnv.YMin = 0;
                PixelBoundsEnv.XMax = pUnitConvertor.ConvertUnits(docGraphicsExtentEnv.XMax, docPageLayout.Page.Units, esriUnits.esriInches) * docExport.Resolution - pUnitConvertor.ConvertUnits(docGraphicsExtentEnv.XMin, docPageLayout.Page.Units, esriUnits.esriInches) * docExport.Resolution;
                PixelBoundsEnv.YMax = pUnitConvertor.ConvertUnits(docGraphicsExtentEnv.YMax, docPageLayout.Page.Units, esriUnits.esriInches) * docExport.Resolution - pUnitConvertor.ConvertUnits(docGraphicsExtentEnv.YMin, docPageLayout.Page.Units, esriUnits.esriInches) * docExport.Resolution;

                //'assign the x and y values representing the clipped export extent to the exportRECT
                exportRECT.bottom = (int)(PixelBoundsEnv.YMax) + 1;
                exportRECT.left = (int)(PixelBoundsEnv.XMin);
                exportRECT.top = (int)(PixelBoundsEnv.YMin);
                exportRECT.right = (int)(PixelBoundsEnv.XMax) + 1;

                //since we're clipping to graphics extent, set the visible bounds.
                docMapExtEnv = docGraphicsExtentEnv;
            }
            else
            {
                double tempratio = iOutputResolution / iScreenResolution;
                double tempbottom = DisplayBounds.bottom * tempratio;
                double tempright = DisplayBounds.right * tempratio;
                //'The values in the exportRECT tagRECT correspond to the width
                //and height to export, measured in pixels with an origin in the top left corner.
                exportRECT.bottom = (int)Math.Truncate(tempbottom);
                exportRECT.left = 0;
                exportRECT.top = 0;
                exportRECT.right = (int)Math.Truncate(tempright);

                //populate the PixelBounds envelope with the values from exportRECT.
                // We need to do this because the exporter object requires an envelope object
                // instead of a tagRECT structure.
                PixelBoundsEnv.PutCoords(exportRECT.left, exportRECT.top, exportRECT.right, exportRECT.bottom);

                //since it's a page layout or an unclipped page layout we don't need docMapExtEnv.
                docMapExtEnv = null;
            }

            // Assign the envelope object to the exporter object's PixelBounds property.  The exporter object
            // will use these dimensions when allocating memory for the export file.
            docExport.PixelBounds = PixelBoundsEnv;