如何使用 grails 从网络摄像头捕获图像并保存？答案

【问题标题】：How to capture an image and save from webcam using grails?如何使用 grails 从网络摄像头捕获图像并保存？
【发布时间】：2015-09-01 14:13:10
【问题描述】：

试图从网络摄像头捕捉图像并希望保存在驱动器上

使用 Grails 2.3.7

脚本代码

var video = document.querySelector("#videoElement");
var imageW;
                //check for getUserMedia support
                navigator.getUserMedia = navigator.getUserMedia
                        || navigator.webkitGetUserMedia
                        || navigator.mozGetUserMedia
                        || navigator.msGetUserMedia || navigator.oGetUserMedia;

                if (navigator.getUserMedia) {
                    // get webcam feed if available
                    navigator.getUserMedia({
                        video : true
                    }, handleVideo, videoError);
                }

                function handleVideo(stream) {

                    video.src = window.URL.createObjectURL(stream);
                }

                function videoError(e) {

                }
                var v, canvas, context, w, h;
                var imgtag = document.getElementById('imgtag'); 
                var sel = document.getElementById('"avatar"'); 

                document.addEventListener('DOMContentLoaded', function() {

                    v = document.getElementById('videoElement');
                    canvas = document.getElementById('canvas');
                    context = canvas.getContext('2d');
                    w = canvas.width;
                    h = canvas.height;

                }, false);

                function draw(v, c, w, h) {

                    if (v.paused || v.ended)
                        return false; // if no video, exit here

                    context.drawImage(v, 0, 0, w, h); // draw video feed to canvas

                    var uri = canvas.toDataURL("image/png"); // convert canvas to data URI


                      imageW = canvas.toDataURL("image/png");
        imageW = imageW.replace('data:image/png;base64,', '');


                    imgtag.src = uri;
                }

                document.getElementById('save').addEventListener('click',
                        function(e) {

                            draw(v, context, w, h); 

                        });


                var fr;

                sel.addEventListener('change', function(e) {
                    var f = sel.files[0]; 

                    fr = new FileReader();
                    fr.onload = receivedData; 

                    fr.readAsDataURL(f); 
                })

                function receivedData() {

                    imgtag.src = fr.result;
                }
                function webImageSubmit() {

                    alert(imageW);

                    var pars = "id=" + $('#id').val() + "&imageW=" + imageW;
                    $.ajax({
                        type : 'POST',
                        url : '/controller_name/saveWebCamImage',
                        data : pars,
                        error : function(request, status, error) {

                            document.getElementById('load').style.visibility = "hidden";
                        },
                        beforeSend : function() {
                            document.getElementById('load').style.visibility = "visible";
                        },
                        success : function(data) {
                            location.reload();
                        }
                    });
                }

控制器端：

def encodedData = javax.xml.bind.DatatypeConverter.parseBase64Binary(params.imageW.toString());
    def defaultPath = "/images/userImages";
        def webRootDir = servletContext.getRealPath("/");
        def systemDir = new File(webRootDir, defaultPath);
        if (!systemDir.exists()) {
            systemDir.mkdirs();
        }

        String file_name = "webImage.jpg";
        def csvFileDir = new File( systemDir, file_name);
        new File(systemDir, file_name).withOutputStream {
            it.write(encodedData);
          };

但是图像没有保存在驱动器上。

请帮帮我.. 谢谢。。

【问题讨论】：

为什么要创建csvFileDir 对象？我没有看到它被使用。变量systemDir 中的完整路径是什么？您确认encodedData 包含数据了吗？运行 webapp 的操作系统用户帐户是否具有对 systemDir 的写入权限？
用于将图像保存在本地驱动器上。
好的...剩下的三个问题呢？

标签： javascript grails webcam-capture

【解决方案1】：

捕获和下载的完整代码

<!DOCTYPE html>
<html>
<head>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script>
$(document).ready(function(){
   const vid = document.querySelector('video');
navigator.mediaDevices.getUserMedia({video: true}) // request cam
.then(stream => {
  vid.srcObject = stream; // don't use createObjectURL(MediaStream)
  return vid.play(); // returns a Promise
})
.then(()=>{ // enable the button
  const btn = document.querySelector('button');
  btn.disabled = false;
  btn.onclick = e => {
    takeASnap()
    .then(download);
  };
});

function takeASnap(){
  const canvas = document.createElement('canvas'); // create a canvas
  const ctx = canvas.getContext('2d'); // get its context
  canvas.width = vid.videoWidth; // set its size to the one of the video
  canvas.height = vid.videoHeight;
  ctx.drawImage(vid, 0,0); // the video
  return new Promise((res, rej)=>{
    canvas.toBlob(res, 'image/jpeg'); // request a Blob from the canvas
  });
}
function download(blob){
  // uses the <a download> to download a Blob
  let a = document.createElement('a'); 
  a.href = URL.createObjectURL(blob);
  a.download = 'screenshot.jpg';
  document.body.appendChild(a);
  a.click();
}
});
</script>
</head>
<body>
<button disabled>
  take a snapshot</button>
<video></video>

</body>
</html>

【讨论】：

【解决方案2】：

完整的代码记录和下载

<!DOCTYPE html>
<html>
<head>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>

</head>
<body>
<button disabled>start recording</button>
<video></video>
<script>
const vid = document.querySelector('video');
navigator.mediaDevices.getUserMedia({video: true}) // request cam
.then(stream => {
  vid.srcObject = stream; // don't use createObjectURL(MediaStream)
  return vid.play(); // returns a Promise
})
.then(()=>{ // enable the button
  const btn = document.querySelector('button');
  btn.disabled = false;
  btn.onclick = startRecording;
});

function startRecording(){
  // switch button's behavior
  const btn = this;
  btn.textContent = 'stop recording';
  btn.onclick = stopRecording;

  const chunks = []; // here we will save all video data
  const rec = new MediaRecorder(vid.srcObject);
  // this event contains our data
  rec.ondataavailable = e => chunks.push(e.data);
  // when done, concatenate our chunks in a single Blob
  rec.onstop = e => download(new Blob(chunks));
  rec.start();
  function stopRecording(){
    rec.stop();
    // switch button's behavior
    btn.textContent = 'start recording';
    btn.onclick = startRecording;
  }
}
function download(blob){
  // uses the <a download> to download a Blob
  let a = document.createElement('a'); 
  a.href = URL.createObjectURL(blob);
  a.download = 'recorded.webm';
  document.body.appendChild(a);
  a.click();
}
</script>
</body>
</html>

【讨论】：

【解决方案3】：

预览捕获图像的代码

<!doctype html>

<html lang="en">
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
    <title>WebcamJS Test Page</title>
    <style type="text/css">
        body { font-family: Helvetica, sans-serif; }
        h2, h3 { margin-top:0; }
        form { margin-top: 15px; }
        form input { margin-right: 15px; }
        #results { float:right; margin:20px; padding:20px; border:1px solid; background:#ccc; }
    </style>
</head>
<body>
    <div id="results">Your captured image will appear here...</div>

    <h1>WebcamJS Test Page</h1>
    <h3>Demonstrates 320x240 capture &amp; display with preview mode</h3>

    <div id="my_camera"></div>

    <!-- First, include the Webcam.js JavaScript Library -->
    <script type="text/javascript" src="webcam.min.js"></script>

    <!-- Configure a few settings and attach camera -->
    <script language="JavaScript">
        Webcam.set({
            width: 320,
            height: 240,
            image_format: 'jpeg',
            jpeg_quality: 90
        });
        Webcam.attach( '#my_camera' );
    </script>

    <!-- A button for taking snaps -->
    <form>
        <div id="pre_take_buttons">
            <input type=button value="Take Snapshot" onClick="preview_snapshot()">
        </div>
        <div id="post_take_buttons" style="display:none">
            <input type=button value="&lt; Take Another" onClick="cancel_preview()">
            <input type=button value="Save Photo &gt;" onClick="save_photo()" style="font-weight:bold;">
        </div>
    </form>

    <!-- Code to handle taking the snapshot and displaying it locally -->
    <script language="JavaScript">
        function preview_snapshot() {
            // freeze camera so user can preview pic
            Webcam.freeze();

            // swap button sets
            document.getElementById('pre_take_buttons').style.display = 'none';
            document.getElementById('post_take_buttons').style.display = '';
        }

        function cancel_preview() {
            // cancel preview freeze and return to live camera feed
            Webcam.unfreeze();

            // swap buttons back
            document.getElementById('pre_take_buttons').style.display = '';
            document.getElementById('post_take_buttons').style.display = 'none';
        }

        function save_photo() {
            // actually snap photo (from preview freeze) and display it
            Webcam.snap( function(data_uri) {
                // display results in page
                document.getElementById('results').innerHTML = 
                    '<h2>Here is your image:</h2>' + 
                    '<img src="'+data_uri+'"/>';

                // swap buttons back
                document.getElementById('pre_take_buttons').style.display = '';
                document.getElementById('post_take_buttons').style.display = 'none';
            } );
        }
    </script>

</body>
</html>

【讨论】：