threshold

Thresholds the image (cv::threshold()): binary, inverted binary, truncated, to zero or inverted to zero, optionally with the threshold of the Otsu’s method.

opencv_apps	1.11.14 and later (ROS 1), 3.0.0 and later (ROS 2)
ROS	noetic, ROS One, jazzy, kilted, lyrical and later
OpenCV	any version of the distributions
Group	Image filters, the nodes of which publish the processed image in `~/image`

Usage

# ROS 2
ros2 launch opencv_apps threshold.launch.xml image:=/camera/image_raw debug_view:=false
# ROS 1
roslaunch opencv_apps threshold.launch image:=/camera/image_raw debug_view:=false

Try it with the demo video

Download the input video of the demo above, publish it as image with image_publisher, and run the node on it, in the terminals:

wget https://ros-perception.github.io/opencv_apps/media/clips/street.mp4
# terminal 1: publish the video as image in a loop
ros2 run image_publisher image_publisher_node street.mp4 --ros-args -p publish_rate:=10.0 -r image_raw:=image
# terminal 2: run the node with the parameters of the demo
ros2 launch opencv_apps threshold.launch.xml image:=image apply_otsu:=true max_binary:=255 threshold:=127 threshold_type:=0
# terminal 3: view the result
ros2 run rqt_image_view rqt_image_view /threshold/image

In ROS 1:

# terminal 1
rosrun image_publisher image_publisher street.mp4 _publish_rate:=10 __name:=camera
# terminal 2
roslaunch opencv_apps threshold.launch image:=camera/image_raw apply_otsu:=true max_binary:=255 threshold:=127 threshold_type:=0

See Credits of the demo videos for the license of the video.

Subscribed topics

Topic	Type
`image`	`sensor_msgs/msg/Image`

Published topics

Topic	Type
`~/image`	`sensor_msgs/msg/Image`

Parameters

Source

src/nodelet/threshold_nodelet.cpp, launch/threshold.launch.xml

Name	Type	Default (range)	Changed at run time	Description
`apply_otsu`	bool	false	yes	Apply otsu threshold
`max_binary`	int	255 (0 - 255)	yes	Max Binary value
`queue_size`	int	3	no, restart the node	Specigy queue_size of input image subscribers
`threshold`	int	150 (0 - 255)	yes	Threshold value
`threshold_type`	int	0 (0 - 4)	yes	Threshold Type, 0: Binary, 1: Binary_Inverted, 2: Threshold_Truncated, 3: Threshold_To_Zero, 4: Threshold_To_Zero_Inverted