Freenect depth maps include a “shadow” on shapes nearer the sensor

[raygeeknyc]

I’m using libfreenect v0.7.5 (latest) on the recent raspberry pi OS (trixie, Debian 13.1) on a Raspberry Pi 5/16GB.

I see the following symptom with my both own code using the Python wrappers and the distributed CPP examples in the freenect Git repository.

All depth sensor depth maps returned by the library include a “shadow” in the depth map that is parallel and offset from distinct shapes in the depth map. This shadow’s offset from the actual shape decreases as the shapes distance from the sensor increases. The shadow disappears at around 4 feet from the sensor.

The attached image is a picture of the freenect demo ‘freenect-cppview’ built as part of the library install:

screen pic of freenect demo

All demos show the same effect.

I’ve disabled the RGB camera, even covering it with tape to make sure it was not the source of this.

In my own code, I’ve tried the different depth map formats “_MM” and “_REGISTERED” which made no difference.

Minimal path to reproduce:

clone the repo at github.com/OpenKinect/libfreenect
Follow build instructions with default options
Connect an Xbox 360 sensor to a USB 3.0 port
Run bin/freenect-cppview

Expected behavior: The depth map, and displayed shapes in the library demo examples, should show the shapes at distinct depths with no "shadow" or offset mirror shape as currently shown in the screen snapshot of the library demo as the black shadow most pronounced around the hands.