Kivy - Camera Handling

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The Kivy framework supports Camera hardware through platform-specific providers. The "opncv-python" package enables camera support for Kivy on most operating systems. Hence it is recommended that the opencv-python package should be installed in Kivy's working environment.

In this chapter, we shall build a Camera app with Kivy library's Camera class. A Camera widget along with a ToggleButton and a normal Button are placed in a vertical box layout to construct the app interface.

The Camera instance starts with the initial play state as True, which means the app window will start the video stream from the camera as soon as it is loaded. The Toggle button stops the camera when it is down. It is bound to play() method. The Capture button will be in enabled state only when the camera is playing.

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

The Capture button saves the current frame to a PNG file by calling export_to_png() method of the Camera object.

As the image is captured, Kivy pops up a message box with a title as Image Captured.

def capture(self, instance):
   if self.tb.text == 'Stop':
      self.mycam.export_to_png("IMG.png")
      layout = GridLayout(cols=1)

      popup = Popup(
         title='Image Captured', title_size=24,
         content=layout, auto_dismiss=True,
         size_hint=(None, None), size=(300, 100)
      )
   popup.open()

The rest of the code involves the composition of the app interface inside the build() method.

Example

The complete code is given below −

from kivy.app import App
from kivy.lang import Builder
from kivy.uix.boxlayout import BoxLayout
from kivy.uix.togglebutton import ToggleButton
from kivy.uix.button import Button
from kivy.uix.popup import Popup
from kivy.uix.camera import Camera
from kivy.core.window import Window

Window.size = (720, 400)

class TestCamera(App):
   def build(self):
      box = BoxLayout(orientation='vertical')
      self.mycam = Camera(play=True, resolution=(640, 480))

      box.add_widget(self.mycam)
      self.tb = ToggleButton(
         text='Stop', size_hint_y=None,
         height='48dp', on_press=self.play
      )
      box.add_widget(self.tb)

      self.cb = Button(
         text='Capture', size_hint_y=None, height='48dp',
         disabled=False, on_press=self.capture
      )
      box.add_widget(self.cb)
      return box
      
   def play(self, instance):
      if instance.state == 'down':
         self.mycam.play = False
         instance.text = 'Play'
         self.cb.disabled = True
      else:
         self.mycam.play = True
         instance.text = 'Stop'
         self.cb.disabled = False
         
   def capture(self, instance):
      if self.tb.text == 'Stop':
         self.mycam.export_to_png("IMG.png")
         layout = GridLayout(cols=1)

         popup = Popup(
            title='Image Captured', title_size=24,
            content=layout, auto_dismiss=True,
            size_hint=(None, None), size=(300, 100)
         )
      popup.open()
      
TestCamera().run()

Output

The camera instance loads as the application starts. Note that depending on the system and the camera device, it may take a few seconds to start. The toggle button's caption is stop and the capture button is enabled.

If you press the Stop button down, the capture button gets disabled. When in enabled state, press the Capture button. The current frame will be saved as "img.png" with a popup box coming up.