Depth Ranging Performance Evaluation and Improvement for RGB-D Cameras on Field-Based High-Throughput Phenotyping Robots

TL;DR

This study evaluates and improves the depth-ranging performance of two RGB-D cameras in in-field high-throughput phenotyping, proposing a compensation strategy to enhance accuracy under challenging outdoor conditions.

Contribution

The paper provides a comprehensive performance evaluation of RealSense D435i and Kinect V2 in field conditions and introduces a novel brightness-and-distance-based error compensation model.

Findings

RealSense D435i has an effective range of 0.160-1.400 m with ~90% filling rate.

Kinect V2 has a range of 0.497-1.200 m with less than 25% filling rate.

The proposed error compensation model reduces lighting and distance effects, achieving a maximum MSE of 0.029.

Abstract

RGB-D cameras have been successfully used for indoor High-ThroughpuT Phenotyping (HTTP). However, their capability and feasibility for in-field HTTP still need to be evaluated, due to the noise and disturbances generated by unstable illumination, specular reflection, and diffuse reflection, etc. To solve these problems, we evaluated the depth-ranging performances of two consumer-level RGB-D cameras (RealSense D435i and Kinect V2) under in-field HTTP scenarios, and proposed a strategy to compensate the depth measurement error. For performance evaluation, we focused on determining their optimal ranging areas for different crop organs. Based on the evaluation results, we proposed a brightness-and-distance-based Support Vector Regression Strategy, to compensate the ranging error. Furthermore, we analyzed the depth filling rate of two RGB-D cameras under different lighting intensities. Experimental results showed that: 1) For RealSense D435i, its effective ranging area is [0.160, 1.400] m, and in-field filling rate is approximately 90%. 2) For Kinect V2, it has a high ranging accuracy in the [0.497, 1.200] m, but its in-field filling rate is less than 24.9%. 3) Our error compensation model can effectively reduce the influences of lighting intensity and target distance. The maximum MSE and minimum R2 of this model are 0.029 and 0.867, respectively. To sum up, RealSense D435i has better ranging performances than Kinect V2 on in-field HTTP.