CameraWidget

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Overview

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Class Definition

class CameraWidget(QWidget):
    """Compact live camera preview."""

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Constants

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Constructor

def __init__(self, parent: QWidget | None = None):

• A QLabel for displaying the video frame (#camera-preview object name)
• Minimum size: 280x210
• Maximum height: 300px
• Maximum width: PREVIEW_WIDTH (280px)
• A QTimer for periodic frame updates (not started until set_camera() is called)

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Layout Structure

• QLabel (_video_label) centered, fixed size 280x210

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Methods

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Binding a Camera

def set_camera(self, camera) -> None:

• camera: A klaus.camera.Camera instance (or None to unbind)

• If camera is not None and camera.is_running is True, starts a 33ms timer (~30 FPS)
• Otherwise, stops the timer

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Updating Frames

def _update_frame(self) -> None:

• If frame width > PREVIEW_WIDTH, scales down using cv2.INTER_AREA interpolation
• Preserves aspect ratio

• Ensures frame is contiguous in memory (np.ascontiguousarray)
• Converts to QImage with Format_RGB888
• Converts to QPixmap and sets on the label

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Stopping

def stop(self) -> None:

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Frame Update Pipeline

1. Timer fires every 33ms (if camera is running)
2. Fetch frame via camera.get_frame_rgb() (returns numpy.ndarray or None)
3. Scale if width > 280px using OpenCV resize
4. Convert to QImage (RGB888 format)
5. Display as QPixmap in the QLabel

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Dependencies

• cv2 (OpenCV): For frame resizing
• numpy: For array operations
• PyQt6: QWidget, QLabel, QTimer, QImage, QPixmap
• klaus.ui.theme: For CAMERA_PREVIEW_WIDTH constant

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Usage Example

from klaus.camera import Camera
from klaus.ui.camera_widget import CameraWidget
from PyQt6.QtWidgets import QApplication

app = QApplication([])
widget = CameraWidget()

# Create and start camera
camera = Camera(device_index=0)
camera.start()

# Bind camera to widget
widget.set_camera(camera)

widget.show()
app.exec()

# Stop preview
widget.stop()
camera.stop()

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Notes

• Frame rate: ~30 FPS (33ms timer interval)
• Scaling: Only width is constrained; height scales proportionally
• No frame drop: If get_frame_rgb() returns None, the widget silently skips the update
• Object name: #camera-preview for QSS styling
• Max dimensions: 280px wide, 300px tall