how to modify and publish camera_info?

edit

Hello.

I would like to make a cropped image from raw image in python.

In my program, I can subscribe /usb_cam/image_raw (sensor_msgs/Image, height=480, width=640) and /usb_cam/camera_info (sensor_msgs/CameraInfo).

Then, I modified roi in /usb_cam/camera_info like below,

edited_camera_info.roi.x_offset = 320
edited_camera_info.roi.y_offset = 240

and publish edited camera info and image.

pub_edited_image.publish(no_edited_image)
pub_edited_camera_info.publish(edited_camera_info)

However, there are no differences between /usb_cam/image_raw and /editted_image_raw.

Is it possible to crop a part of an image by modifying camera_info? Or, is there any alternative ways to realize to crop an image?