如何在asp.net中从gridview导出图像到excel？

I have a ASPxGridView consist of a image column. When I click the ExportToPDF,images are shown in pdf. But if I click the ExportToXls, images are not shown in the excel. What is the problem ? I use Devexpress 14.2 in visual studio. P.S. = Images in gridview are different sizes.I have a ASPxGridView consist of a image column