example

function toDataUrl(url, callback) {
    var xhr = new XMLHttpRequest();
    xhr.onload = function() {
        var reader = new FileReader();
        reader.onloadend = function() {
            callback(reader.result);
        }
        reader.readAsDataURL(xhr.response);
    };
    xhr.open('GET', url);
    xhr.responseType = 'blob';
    xhr.send();
}
toDataUrl(<?php echo "'".$this->baseurl."/templates/jjview/images/Aarshjul_bg.jpg"."'"; ?>, function(myBase64) {
    doc.addImage(myBase64, 'JPEG', 0, 0, width, height );
    doc.addImage(canvasImg, 'JPEG', marginL, marginT, chartW, chartH );
    doc.setFont('TSTARPRO-Bold');
    //doc.setFontType("bold");
    doc.setFontSize(27);
    doc.setTextColor(255,255,255);
    doc.text(47, 40, 'ÅRSHJUL');
    doc.setFont('TSTARPRO-Regular');
    doc.text('Hi How are you', width-47, 40, 'right');
    doc.save('canvas.pdf');
});