HTML2canvas generates Blurry images

问题

I am using jsPDF and it uses html2canvas to generate an image from some html element and insert on the .pdf file. But there is a problem on html2canvas, it generates blurry images from the html. See example below:

HTML content:

http://puu.sh/7SZz4.png

html2canvas generated image:

http://puu.sh/7SZAT.png

Is there any way to fix it or is there any better option to get the image form html?

thanks!

回答1:

you can use scale options in html2canvas.

In the latest release, v1.0.0-alpha.1, you can use the scale option to increase the resolution (scale: 2 will double the resolution from the default 96dpi).

// Create a canvas with double-resolution.
html2canvas(element, {
    scale: 2,
    onrendered: myRenderFunction
});
// Create a canvas with 144 dpi (1.5x resolution).
html2canvas(element, {
    dpi: 144,
    onrendered: myRenderFunction
});

回答2:

I had this problem because I was on a retina display. I solved in by using MisterLamb's solution here.

$(window).load(function () {

    var scaleBy = 5;
    var w = 1000;
    var h = 1000;
    var div = document.querySelector('#screen');
    var canvas = document.createElement('canvas');
    canvas.width = w * scaleBy;
    canvas.height = h * scaleBy;
    canvas.style.width = w + 'px';
    canvas.style.height = h + 'px';
    var context = canvas.getContext('2d');
    context.scale(scaleBy, scaleBy);

    html2canvas(div, {
        canvas:canvas,
        onrendered: function (canvas) {
            theCanvas = canvas;
            document.body.appendChild(canvas);

            Canvas2Image.saveAsPNG(canvas);
            $(body).append(canvas);
        }
    });
});

HTML and PNG without scaling

HTML and PNG with scaling

回答3:

I have found out my problem. Happens that my screen is a Retina Display, so when the canvas2html will render the HTML, due to the difference of pixel density on retina screen, the image is rendered blurred.

Found out the solution here:

https://github.com/cburgmer/rasterizeHTML.js/blob/master/examples/retina.html

回答4:

This is what fixed it for me. And it wasn't because I was using a retina display (because I don't have one):

https://github.com/niklasvh/html2canvas/issues/576

Just change the getBounds() method in html2canvas.js with this one:

 function getBounds (node) {
        if (node.getBoundingClientRect) {
            var clientRect = node.getBoundingClientRect();
            var width = node.offsetWidth == null ? clientRect.width : node.offsetWidth;
            return {
                top   : Math.floor(clientRect.top),
                bottom: Math.floor(clientRect.bottom || (clientRect.top + clientRect.height)),
                right : Math.floor(clientRect.left + width),
                left  : Math.floor(clientRect.left),
                width : width,
                height: node.offsetHeight == null ? clientRect.height : node.offsetHeight
            };
        }
        return {};
    }

回答5:

Try the Canvas2Image library, it gives a better quality image at least for me div to image (fiddle).

    html2canvas($("#widget"), {
        onrendered: function(canvas) {
            theCanvas = canvas;
            Canvas2Image.saveAsPNG(canvas);  // Convert and download as image with a prmompt. 
        }
    });

Good luck!

来源：https://stackoverflow.com/questions/22803825/html2canvas-generates-blurry-images

标签

javascript

html

canvas

html2canvas

jspdf