In the paper we used a very intuitive idea of mapping distance between the surgical instrument to the color spectrum.
For evaluation we conducted a user study using a within subjects experiment design with 12 subjects. We evaluated CDE in both stereoscopic and monocular conditions. The four conditions are Stereo (S) + Color-Depth Encoding (CDE), Stereo + No CDE, No Stereo + CDE and No Stereo + No CDE. Results show significantly less error in depth judgements in Stereo + CDE case when compared to other cases. Subjects also took significantly less time in Stereo + CDE case. For details of the task please see the paper. The method can be seen in the video shown below.
Kalia, M., Navab, N., & Salcudean, T. (2019, May). A real-time interactive augmented reality depth estimation technique for surgical robotics. In 2019 International Conference on Robotics and Automation (ICRA) (pp. 8291-8297). IEEE.