Kivy - Camera

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With the Camera widget in Kivy, it is possible to display the video stream from a camera device. Kivy may take some time to initialize the camera device, and update the widget texture afterwards.

The Camera class is defined in the "kivy.uix.camera: module.

from kivy.uix.camera import Camera
cam = Camera(**kwargs)

If the system finds multiple camera devices, you need to specify the camera to be used by its index.

cam = Camera(index=1)

You can also specify the camera resolution with the resolution argument −

cam = Camera(index=1, resolution=(640, 480))

The kivy.uix.camera.Camera class is a concrete implementation of the core Camera class from the "kivy.core.camera" module, and performs the initialization and frame capture functions.

Kivy needs to find an appropriate camera provider to be able to detect the hardware. For this purpose, install the latest version of opencv-python package, which also installs its dependency packages including NumPy.

pip install opencv-python

To start streaming the feed from your camera on the app window, set the play property of the Camera object to True, and set it to False to stop the feed.

cam.play = True

To capture the snapshot of the camera stream to an image, use the export_to_png() method. Specify the filename to save to.

The Camera class defines following attributes −

• index − Index of the used camera, starting from 0. Setting it to -1 to allow auto selection.

• play − Boolean indicating whether the camera is playing or not. You can start/stop the camera by setting this property −

# create the camera, and start later (default)
cam = Camera()

# and later
cam.play = True

# to sop
cam.play = False

• resolution − Preferred resolution to use when invoking the camera. If you are using [-1, -1], the resolution will be the default one. To set the desired resolution, provided it is supported by the device −

cam = Camera(resolution=(640, 480))

Example

The following example code adds a Camera widget and a ToggleButton inside a vertical BoxLayout. The callback bound to the toggle button sets the camera object's play property to True when the button is down, and otherwise the video is stopped.

from kivy.app import App
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.togglebutton import ToggleButton
from kivy.uix.camera import Camera
from kivy.core.window import Window

Window.size = (720,350)

class TestCameraApp(App):
   def build(self):
      box=BoxLayout(orientation='vertical')
      self.mycam=Camera(play=False, resolution= (640, 480))
      box.add_widget(self.mycam)
      tb=ToggleButton(text='Play', size_hint_y= None, height= '48dp')
      tb.bind(on_press=self.play)
      box.add_widget(tb)
      return box

   def play(self, instance):
      if instance.state=='down':
         self.mycam.play=True
         instance.text='Stop'
      else:
         self.mycam.play=False
         instance.text='Play'
         
TestCameraApp().run()

Output

Run the code and check the output −

You can also use the "kv" language script to design the application window layout. Save the following script as "TestCamera.kv", comment out the code in the build() method, and just place a "pass" statement in it.

BoxLayout:
   orientation: 'vertical'
   Camera:
      id: camera
      resolution: (640, 480)
      play: False
   ToggleButton:
      text: 'Play'
      on_press: camera.play = not camera.play
      size_hint_y: None
      height: '48dp'