black white instead depth image from /zed/depth/depth_registered

edit

If you view the depth image in RVIZ it will show as a black and white image. The pixel values are actually the depth in metres with undefined pixels set to zero. When RVIZ views these it assumes the pixels are float intensity values which a clamped between 0-1. This results in almost the entire image being white with some black areas where the depth is not defined.

There is a point cloud topic you can subscribe to which will show a 3D view of the depth data, or if you subscribe to the depth topic in your own node you can use the full range of the depth data in metres.

Hope this helps.