How to color the pcd Pointcloud using RGB image.

### Checklist

- [X] I have searched for [similar issues](https://github.com/isl-org/Open3D/issues).
- [X] For Python issues, I have tested with the [latest development wheel](http://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [X] I have checked the [release documentation](http://www.open3d.org/docs/release/) and the [latest documentation](http://www.open3d.org/docs/latest/) (for `master` branch).

### My Question

Hi, I have a pointcloud in a pcd file format extracted from a rosbag. I also have the RGB image at the same timestamp of rosbag. Both the LiDar and camera are capturing the same field of view. The sensors are set a few centimeters apart. I dont have any colors in pointcloud.

My question is : **How can i colorize the pointcloud using RGB information of image.**

The image have a size of

> Image of size 960x540, with 4 channels.

The pointcloud have number of points (65536,3) .
I am working with pcd and image using numpy array, i have tried but not able to get the color information of each pixel in image. Does open3d have a method to extract the color information from image ?