equalize_histogram

Equalizes the histogram of the image (cv::equalizeHist() or CLAHE) to improve its contrast.

opencv_apps	2.0.3 and later (ROS 1), 3.0.0 and later (ROS 2)
ROS	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 equalize_histogram.launch.xml image:=/camera/image_raw debug_view:=false
# ROS 1
roslaunch opencv_apps equalize_histogram.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 equalize_histogram.launch.xml image:=image clahe_clip_limit:=20.0 clahe_tile_size_x:=32 clahe_tile_size_y:=32 histogram_equalization_type:=1 node_name:=equalize_histogram_clahe use_opencl:=false
# terminal 3: view the result
ros2 run rqt_image_view rqt_image_view /equalize_histogram_clahe/image

CLAHE.

In ROS 1:

# terminal 1
rosrun image_publisher image_publisher street.mp4 _publish_rate:=10 __name:=camera
# terminal 2
roslaunch opencv_apps equalize_histogram.launch image:=camera/image_raw clahe_clip_limit:=20.0 clahe_tile_size_x:=32 clahe_tile_size_y:=32 histogram_equalization_type:=1 node_name:=equalize_histogram_clahe use_opencl:=false

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/equalize_histogram_nodelet.cpp, launch/equalize_histogram.launch.xml

Name	Type	Default (range)	Changed at run time	Description
`clahe_clip_limit`	double	20.0 (0 - 255)	yes	Clip Limit for Clahe filter
`clahe_tile_size_x`	int	32 (0 - 300)	yes	X Tile Size for Clahe filter
`clahe_tile_size_y`	int	32 (0 - 300)	yes	Y Tile Size for Clahe filter
`histogram_equalization_type`	int	0 (0 - 1)	yes	Histogram Equalization Methods, 0: EqualizeHist, 1: Clahe
`queue_size`	int	3	no, restart the node	Specigy queue_size of input image subscribers
`use_opencl`	bool	true	no, restart the node	Enable or disable OpenCL