从guriddo jqgrid导出pdf时如何添加徽标？

Question

j$("#jqGrid").jqGrid("exportToPdf", {
      title: 'Quick Pricing Estimate',
      background: 'simple text',
      orientation: 'landscape',
      pageSize: 'legal',
      description: 'Pricing estimates are subject to change.',
      download: 'download',
      includeLabels : true,
      includeGroupHeader : true,
      includeFooter: true,
      customSettings: null,
      fileName : "jqGridExport.pdf",
      mimetype : "application/pdf", 
      onBeforeExport : function( doc ) 
      {
              doc.styles.tableBody.fontSize = 8;
              doc.styles.title.alignment = 'left';
              doc.styles.description.color = '#FF0000';
      }
})