protected override void OnClick()

         {

             //

             //  TODO: Sample code showing how to access button host

             //

             ArcMap.Application.CurrentTool = null;

             IMap pMap = ArcMap.Document.FocusMap;

             for (int i = ; i < pMap.LayerCount; i++)

             {

                 ILayer pLayer = pMap.get_Layer(i);

                 if (pLayer is IRasterLayer)

                 {

                     IRasterLayer pRstLyr = pLayer as IRasterLayer;

                     IRasterStretchColorRampRenderer pRasterStretchColorRampRenderer;

                     IRasterStretch2 prstStretch= pRstLyr.Renderer as IRasterStretch2;

                     // Setup the stretch

                     prstStretch.Background = true;

                     // Apply the renderer

                     pRstLyr.Renderer = (IRasterRenderer)prstStretch;

                     // Collapse the legends on each raster

                     ILegendInfo legendInfo = (ILegendInfo)pRstLyr.Renderer;

                     ILegendGroup legendGroup = (ILegendGroup)legendInfo.get_LegendGroup();

                     legendGroup.Visible = false;

                 }

             }

         }