Using transformation matrix

[Gold3nFox]

After running and copying transformation matrix from terminal I'm trying to use that transformation matrix to extract color from image and add it to pcd output of velodyne lidar, I used open3d to read point cloud and extract each point which has x and y and z and transformed it with transformation matrix.
Range of each point before and after transformation is :
x: -6.706142902374268 -> 39.4197998046875
y: -65.62940216064453 -> 6.3055100440979
z: -0.8670438528060913 -> 9.03710079193
But pictures x and y is from 0 to page width pixel , 0 to page height pixel
I'm new to this and i don't really know how to use x and y and z after transformation to get that pixel from image, I assumed i should ignore z as the image is 2d.