javascript - HTML5 canvas, save jpeg blob and restore to canvas from blob - Stack Overflow

admin管理员组

文章数量:1344979

I have a canvas #mycanvas which contains an image. I want to create a blob out of that image, preferably as a jpeg. Here is how i create the blob

document.getElementById('mycanvas').toDataURL("image/jpeg").replace(/^data:image\/(png|jpeg);base64,/, "")

How do i recreate the image from this blob, and show it in #mycanvas again?

I have a canvas #mycanvas which contains an image. I want to create a blob out of that image, preferably as a jpeg. Here is how i create the blob

document.getElementById('mycanvas').toDataURL("image/jpeg").replace(/^data:image\/(png|jpeg);base64,/, "")

How do i recreate the image from this blob, and show it in #mycanvas again?

• javascript
• html
• html5-canvas

Share Improve this question Follow asked Aug 24, 2013 at 13:46 Anton GildebrandAnton Gildebrand 3,7171313 gold badges5252 silver badges9292 bronze badges 3

• 1 Check out the answer here stackoverflow./questions/4773966/… – Sergiu Paraschiv Commented Aug 24, 2013 at 14:08
• 2 May I suggest that the word "blob" is probably a little misleading ? As shown on MDN the right way to convert a <canvas> content into a Blob is to use the .toBlob() method, not at all .toDataURL(). In fact your question should have probably been HTML5 canvas, save jpeg data URL and restore to canvas from data URL. What do you think ? – danidemi Commented Aug 3, 2016 at 16:51
• 1 A data URL is a base64 representation of the image not a Blob. As danidemi pointed out. See: developer.mozilla/en-US/docs/Web/API/HTMLCanvasElement/… and developer.mozilla/en-US/docs/Web/API/HTMLCanvasElement/… – Björn Commented Feb 22, 2017 at 14:09

Add a ment  | 

3 Answers 3

Sorted by: Reset to default 4

Here's how i solved my problem

function blob2canvas(canvas,blob){
    var img = new Img;
    var ctx = canvas.getContext('2d');
    img.onload = function () {
        ctx.drawImage(img,0,0);
    }
    img.src = blob;
}

The blob was received when calling canvas.toDataURL("image/jpeg")

Anton's answer no longer works as it is. You need this syntax now.

function blob2canvas(canvas,blob){
    var img = new window.Image();
    img.addEventListener("load", function () {
        canvas.getContext("2d").drawImage(img, 0, 0);
    });
    img.setAttribute("src", blob);
}

Restore to Canvas from Blob sample taken from: https://googlechrome.github.io/samples/image-capture/grab-frame-take-photo.html

// ms is a MediaStreamPointer
let imageCapture = new ImageCapture(ms.getVideoTracks()[0]);

                imageCapture.takePhoto()
                    .then(blob => createImageBitmap(blob))
                    .then(imageBitmap => {
                        const canvas = document.getElementById('canvas')
                        drawCanvas(canvas, imageBitmap);
                    })

function drawCanvas(canvas, img) {
    canvas.width = getComputedStyle(canvas).width.split('px')[0];
    canvas.height = getComputedStyle(canvas).height.split('px')[0];
    let ratio = Math.min(canvas.width / img.width, canvas.height / img.height);
    let x = (canvas.width - img.width * ratio) / 2;
    let y = (canvas.height - img.height * ratio) / 2;
    canvas.getContext('2d').clearRect(0, 0, canvas.width, canvas.height);
    canvas.getContext('2d').drawImage(img, 0, 0, img.width, img.height,
        x, y, img.width * ratio, img.height * ratio);
}

本文标签： javascriptHTML5 canvassave jpeg blob and restore to canvas from blobStack Overflow