Javascript html2canvas和toDataURL生成的图像具有水平线

我正在循环处理10-14个html元素，并在数组中生成图像数据，以便以后插入PDF。问题是这些图像偶尔会有一条横线，这似乎是html2canvas存在的问题。主要发生在FF和IE中，偶尔也发生在Chrome上，但不太常见

function convertElementsToImages(containerSelector) {
    if (_this.pdfDebug) {
        window.console.log('convertElementsToImages');
        window.console.log(containerSelector);
    }

    var eles = $(containerSelector + ' > *'),
        q = $q.defer(),
        temp = [];

        //convert to canvas
        angular.forEach(eles, function(ele, eleKey) {
            convertElementToImage(ele).then(function(imageData) {
                temp[eleKey] = imageData;

                //last one, hopefully all previous elements have been resolved
                if (eles.length === eleKey + 1) {
                    q.resolve(temp);
                }
            });
        });

    return q.promise;
}

function convertElementToImage(element) {
    var q = $q.defer();

    html2canvas($(element)[0], { // jshint ignore:line
        onrendered: function(canvas) {
            q.resolve(canvas.toDataURL('image/jpeg'));
        }
    });
    return q.promise;
}