Question

人！

我正在尝试制作一个演示用户可以通过浏览器从网络摄像头捕获图像，这个图像将通过使用AJAX传递给PHP服务保存在后端调用

我能够捕获画布但不能将其转换为图像数据。我得到了canvas is undefined error

安装非常简单。

HTML

<video id="videoElement"  autoplay></video>
<button id="snap">Snap Photo</button>
<canvas id="canvas" style="display:none" ></canvas>

JAVASCRIPT

    // Grab elements, create settings, etc.
    var video = document.getElementById('videoElement');

    // Get access to the camera!
    if(navigator.mediaDevices && navigator.mediaDevices.getUserMedia) {
        // Not adding `{ audio: true }` since we only want video now
        navigator.mediaDevices.getUserMedia({ video: true }).then(function(stream) {
            video.src = window.URL.createObjectURL(stream);
            video.play();
        });
    }

    // Elements for taking the snapshot
    var canvas = document.getElementById('canvas');
    var context = canvas.getContext('2d');
    var video = document.getElementById('videoElement');

    // Trigger photo take
    document.getElementById("snap").addEventListener("click", function() {
      var cann= context.drawImage(video, 0, 0, 640, 480); //draw canvas
    //then convert canvas to image so i can obtain dataurl
    //and pass it to another function using AJAX
      var img= convertCanvasToImage(cann);
    console.log(img);
    });

// Converts canvas to an image
function convertCanvasToImage(canvas) 
{
    var image = new Image();
    image.src = canvas.toDataURL("image/png");
    return image;
}

我对这个领域很陌生。我还有一个问题。这适用于最新的浏览器吗？任何人都可以帮我弄清楚我犯的错误吗？

FIDDLE

参考： https://davidwalsh.name/browser-camera

https://davidwalsh.name/convert-canvas-image

Answer 1

请致电

 var img= convertCanvasToImage();

function convertCanvasToImage() 
{
  var image = new Image();
  image.src = canvas.toDataURL("image/png");
  return image;
}

无需像上面定义的画布那样传递画布。但是如果你在另一个文件中有convertCanvasToImage函数，那么你可以使用

var img= convertCanvasToImage(canvas);

Answer 2

这可能有所帮助。

function demoFromHTML() {
    html2canvas(document.getElementById("talltweets"), {
        onrendered: function(canvas) {
            var imageData = canvas.toDataURL('image/png',1.0); 

        }
    });
}

Answer 3

传递canvas对象而不是cann

var img= convertCanvasToImage(canvas);

Answer 4

如果您可以尝试避免使用dataURL并使用blob，那么它将为您节省更多内存并load images faster

$canvas.toBlob(function(blob){
  var url = URL.createObjectURL(blob)
  var img = new Image

  img.onload = function() {
    URL.revokeObjecURL(this.src)
  }
  img.src = url
  
  console.log(blob)
  console.log(url)
})

<canvas id="$canvas">

您可以使用polyfill来支持canvas＃toBlob

javascript-无法将画布转换为图像数据

4 个答案: