Capturing an image in HTML5 at full resolution

问题

It is possible to capture an image in javascript using the MediaStream API. But in order to do so it is first necessary to instantiate a video object, then paint a frame into a canvas to get an image. But unfortunately many devices (e.g. phones) don't allow you to capture a video at the full native resolution of the device. For instance, on my phone the maximum image resolution is on the order of 4000x3000 but the maximum video resolution is a mere 1920x1080. Obviously capturing an image which is only barely 1/6th of the available resolution is unacceptable.

So how can I access the full resolution of the camera on the device?

回答1:

You can't record a full-resolution picture using the MediaStream API, but you can use the Media Capture API.

The MediaStream API is able stream data from the camera, but as a video at a video resolution. This is why you can't make photos with a high resolution.

The alternative is to use the Media Capture API. It simply overrides the HTMLInput element by adding a capture=camera to the accept parameter. The result is that the native photo app opens to take a picture. This feature is currently (Nov 2017) only implemented in mobile browsers, so you still need WebRTC as a fallback if you need to support this feature on the desktop.

Working example

var myInput = document.getElementById('myFileInput');

function sendPic() {
    var file = myInput.files[0];

    // Send file here either by adding it to a `FormData` object 
    // and sending that via XHR, or by simply passing the file into 
    // the `send` method of an XHR instance.
    
    console.log(file);
}

myInput.addEventListener('change', sendPic, false);

<input id="myFileInput" type="file" accept="image/*" capture="camera">

I feel like the current situation of the MediaStream API is to access the camera of a desktop and not to actually use it to take photos with.

来源：https://stackoverflow.com/questions/36275253/capturing-an-image-in-html5-at-full-resolution

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javascript

html5

getusermedia

mediastream