Add a basic example script on working with the camera

clover/examples/camera.py

@@ -0,0 +1,64 @@
+# Information: https://clover.coex.tech/camera
+
+# Example on basic working with the camera and image processing:
+
+# - cuts out a central square from the camera image;
+# - publishes this cropped image to the topic `/cv/center`;
+# - computes the average color of it;
+# - prints its name to the console. 
+
+import rospy
+import cv2
+from sensor_msgs.msg import Image
+from cv_bridge import CvBridge
+from clover import long_callback
+
+rospy.init_node('cv')
+bridge = CvBridge()
+
+printed_color = None
+center_pub = rospy.Publisher('~center', Image, queue_size=1)
+
+def get_color_name(h):
+    if h < 15: return 'red'
+    if h < 30: return 'orange'
+    elif h < 60: return 'yellow'
+    elif h < 90: return 'green'
+    elif h < 120: return 'cyan'
+    elif h < 150: return 'blue'
+    elif h < 170: return 'magenta'
+    else: return 'red'
+
+
+@long_callback
+def image_callback(msg):
+    img = bridge.imgmsg_to_cv2(msg, 'bgr8')
+
+    # convert to HSV to work with color hue
+    img_hsv = cv2.cvtColor(img, cv2.COLOR_BGR2HSV)
+
+    # cut out a central square
+    w = img.shape[1]
+    h = img.shape[0]
+    r = 20
+    center = img_hsv[h // 2 - r:h // 2 + r, w // 2 - r:w // 2 + r]
+
+    # compute and print the average hue
+    mean_hue = center[:, :, 0].mean()
+    color = get_color_name(mean_hue)
+    global printed_color
+    if color != printed_color:
+        print(color)
+        printed_color = color
+
+    # publish the cropped image
+    center = cv2.cvtColor(center, cv2.COLOR_HSV2BGR)
+    center_pub.publish(bridge.cv2_to_imgmsg(center, 'bgr8'))
+
+# process every frame:
+image_sub = rospy.Subscriber('main_camera/image_raw', Image, image_callback, queue_size=1)
+
+# process 5 frames per second:
+# image_sub = rospy.Subscriber('main_camera/image_raw_throttled', Image, image_callback, queue_size=1)
+
+rospy.spin()