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Capture picture from your Webcam in Angular

Use case

If you trade crypto often, you will notice that their verification process involves a step to upload a photo of you with your identity card. Or you can capture it via webcam. Refer to the below picture taken from Binance.

Capture picture from your Webcam in Angular

After selecting the Take Photo option, it will ask for your permission to use the webcam. If you allow, then you can start to take a photo with your webcam.

Output

We will build something similar to the output below.

Capture picture from your Webcam in Angular

Web API MediaDevices

The MediaDevices interface provides access to connected media input devices like cameras and microphones and screen sharing. In essence, it lets you obtain access to any hardware source of media data.

We will utilize the MediaDevices for accessing the webcam. Some methods worth mentioning:

  • navigator.mediaDevices.enumerateDevices(): requests a list of the available media input and output devices, such as microphones, cameras, headsets, and so forth.
  • getUserMedia(): with the user’s permission through a prompt, turns on a camera and/or a microphone on the system

It will ask for your permission, similar to the below photo.

Capture picture from your Webcam in Angular

WebcamSnapshotModule

I started by creating a new fresh:

  • WebcamSnapshotComponent
  • WebcamSnapshotModule

SCAMs (single component Angular modules) are Angular modules scoped to a single declarable, and you should follow that to create reusable pieces for your application.

Refer to the below step how to do it on stackblitz

Capture picture from your Webcam in Angular

One additional step I need to do it to export WebcamSnapshotComponent on the WebcamSnapshotModule

@NgModule({
  imports: [CommonModule],
  declarations: [WebcamSnapshotComponent],
  exports: [WebcamSnapshotComponent],
})
export class WebcamSnapshotModule {}

WebcamSnapshotComponent

Now we have the component and module ready. Let go ahead and write the actual code for accessing the webcam.

webcam-snapshot.component.html

Open webcam-snapshot.component.html and put in the code.

<div class="video-container">
  <video
    [class.show]="!isCaptured"
    [class.hide]="isCaptured"
    #video
    id="video"
    [width]="WIDTH"
    [height]="HEIGHT"
    autoplay
  ></video>
  <canvas
    [class.show]="isCaptured"
    [class.hide]="!isCaptured"
    #canvas
    id="canvas"
    [width]="WIDTH"
    [height]="HEIGHT"
  ></canvas>
</div>

<div class="snap-container">
  <button class="btn btn-primary" *ngIf="!isCaptured" (click)="capture()">
    Snap Photo
  </button>
</div>

I have a video tag for displaying the webcam stream. Also, a canvas to render the image after taking the photo with a button name Snap Photo. Please be noted that both video and canvas have the template reference by using # to access it using ViewChild.

webcam-snapshot.component.ts

Now let look at the code that does the heavy lifting part.

export class WebcamSnapshotComponent implements AfterViewInit {
  WIDTH = 640;
  HEIGHT = 480;

  @ViewChild("video")
  public video: ElementRef;

  @ViewChild("canvas")
  public canvas: ElementRef;

  captures: string[] = [];
  error: any;
  isCaptured: boolean;

  async ngAfterViewInit() {
    await this.setupDevices();
  }

  async setupDevices() {
    if (navigator.mediaDevices && navigator.mediaDevices.getUserMedia) {
      try {
        const stream = await navigator.mediaDevices.getUserMedia({
          video: true
        });
        if (stream) {
          this.video.nativeElement.srcObject = stream;
          this.video.nativeElement.play();
          this.error = null;
        } else {
          this.error = "You have no output video device";
        }
      } catch (e) {
        this.error = e;
      }
    }
  }

  capture() {
    this.drawImageToCanvas(this.video.nativeElement);
    this.captures.push(this.canvas.nativeElement.toDataURL("image/png"));
    this.isCaptured = true;
  }

  drawImageToCanvas(image: any) {
    this.canvas.nativeElement
      .getContext("2d")
      .drawImage(image, 0, 0, this.WIDTH, this.HEIGHT);
  }
}

I have:

  • WIDTH and HEIGHT const for the webcam and canvas size
  • video and canvas refer to the template using the template reference. By default, you can only access them after the view has been init using ngAfterViewInit. That’s why I implement AfterViewInit interface instead of OnInit hook. See more about that
  • setupDevices is where I start to ask for permission using video. getUserMedia return a Promise. That’s why I am using async/await. You could still use then if you are comfortable with that. Noted that the returned stream could be null if your device has no video output device.
  • capture is to take the current video screenshot and draw it into our canvas using drawImageToCanvas. At the same time, I also push the data into the captures array. It is just base64 encoded image data. You could use that for uploading to the server if required.

Capture picture from your Webcam in Angular

Source code and demo

Please open this stackblitz in a new window for testing. If it is not working, try click Refresh on stackblitz.

It happens to me as well :(

Capture picture from your Webcam in Angular

Conclusion

You just saw how to use Angular to capture images from the webcam using a web browser. You can always use a library for that purpose. But it is essential to understand how things work under the hood :)

Reference

Published 16 Jan 2021

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