IRasterLayer里面的Renderer使用RasterRGBRendererClass，StretchType设置为NONE。以下是我将图像转换为img格式，采用RLE无损压缩。

IRasterLayer rasterLayer = new RasterLayerClass();
rasterLayer.CreateFromFilePath(strFromName);
IRaster pRaster = rasterLayer.Raster;
RasterRGBRendererClass pRasterRenderer = new RasterRGBRendererClass();
pRasterRenderer.StretchType = esriRasterStretchTypesEnum.esriRasterStretch_NONE;
rasterLayer.Renderer = pRasterRenderer;
IRasterProps pRasterProps = (IRasterProps)pRaster;
IRasterLayerExport3 rLayerExport = new RasterLayerExportClass();
rLayerExport.Force2RGB = true;
IRasterStorageDef2 pRasterStorageDef = new RasterStorageDefClass();
pRasterStorageDef.PyramidResampleType = rstResamplingTypes.RSP_BilinearInterpolation;
pRasterStorageDef.CompressionType = esriRasterCompressionType.esriRasterCompressionRLE;
//pRasterStorageDef.CompressionQuality = 70; 只有有损压缩的情况，这个属性设置才生效
rLayerExport.StorageDef = pRasterStorageDef;
rLayerExport.RasterLayer = rasterLayer;
rLayerExport.Extent = pRasterProps.Extent;//设置提取栅格数据的范围即为Raster数据的范围
rLayerExport.SpatialReference = pRasterProps.SpatialReference;// 设置当前栅格数据的投影信息
rLayerExport.NoData = null;
string strFolderName = this.txtPathOutput.Text; //ofDlg.FileName.Substring(0, ofDlg.FileName.LastIndexOf('\\'));
IWorkspaceFactory pWF = new RasterWorkspaceFactoryClass();
IWorkspace pRasterWorkspace = pWF.OpenFromFile(strFolderName, 0);
IRasterDataset dataset = rLayerExport.Export(pRasterWorkspace, string.Concat(System.IO.Path.GetFileNameWithoutExtension(strFromName), ".img"), "IMAGINE Image");