Very simple example streaming from an opencv camera (#1502)

* Very simple example streaming from an opencv camera

* Warning about the memory limitations

* Update comments and link to known issue

---------

Co-authored-by: Clement Rey <[email protected]>

examples/python/opencv_canny/main.py

@@ -0,0 +1,96 @@
+#!/usr/bin/env python3
+"""
+Very simple example of capturing from a live camera.
+
+Runs the opencv canny edge detector on the image stream.
+
+Known issues:
+ - Only two layers of image transparency are visible. [#1503](https://github.com/rerun-io/rerun/issues/1503)
+
+NOTE: this example currently runs forever and will eventually exhaust your
+system memory. It is advised you run an independent rerun viewer with a memory
+limit:
+```
+rerun --memory-limit 4GB
+```
+
+And then connect using:
+```
+python examples/python/opencv_canny/main.py --connect
+```
+
+"""
+
+import argparse
+
+import cv2
+import rerun as rr
+
+
+def run_canny() -> None:
+    # Create a new video capture
+    cap = cv2.VideoCapture(0)
+
+    while cap.isOpened():
+        # Read the frame
+        ret, img = cap.read()
+        if not ret:
+            print("Can't receive frame (stream end?). Exiting ...")
+            break
+
+        # Get the current frame time
+        frame_time = cap.get(cv2.CAP_PROP_POS_MSEC)
+        rr.set_time_nanos("frame_time", int(frame_time * 1000000))
+
+        # Log the original image
+        rgb = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)
+        rr.log_image("image/rgb", rgb)
+
+        # Convert to grayscale
+        gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
+        rr.log_image("image/gray", gray)
+
+        # Run the canny edge detector
+        canny = cv2.Canny(gray, 50, 200)
+        rr.log_image("image/canny", canny)
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser(description="Streams a local system camera and runs the canny edge detector.")
+    parser.add_argument(
+        "--device", type=int, default=0, help="Which camera device to use. (Passed to `cv2.VideoCapture()`)"
+    )
+
+    rr.script_add_args(parser)
+    args = parser.parse_args()
+
+    rr.script_setup(args, "opencv_canny")
+
+    print(args.connect)
+
+    if not args.connect:
+        print(
+            """
+################################################################################
+NOTE: this example currently runs forever and will eventually exhaust your
+system memory. It is advised you run an independent rerun viewer with a memory
+limit:
+```
+rerun --memory-limit 4GB
+```
+
+And then connect using:
+```
+python examples/python/opencv_canny/main.py --connect
+```
+################################################################################
+        """
+        )
+
+    run_canny()
+
+    rr.script_teardown(args)
+
+
+if __name__ == "__main__":
+    main()

examples/python/opencv_canny/requirements.txt

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+opencv-python
+rerun-sdk