Introduction

Objective: Find a tool to determine relative ground cover of living plants, plant residues, and bare soil by batch processing digital images.

• Ground cover by crops can be an important tool for quantifying plant vigor in genotypic trials. Ground cover by crops or crop residues is an important modifier of the soil surface environment and affects germination and establishment of weeds.
• The accessibility of digital photography and computing power makes analysis of images an attractive tool for determining ground cover in field experiments.
• Preliminary analysis (see next page) showed that low red:green color ratio was generally diagnostic of green tissue, and that high intensity was typical of residue. The commercial (proprietary) image analysis software tools we examined did not support the use of color ratios or the use of multiple thresholds.
• Free and Open Source Software (FOSS) includes several useful programs that together can provide a flexible set of tools for analyzing images. These tools may require customization to maximize their usefulness to particular applications.
• ImageJ: a free image analysis tool from the US National Institutes of Health. We use ImageJ mostly for pixel sampling, but it is a powerful tool, with many available plugins.
• R: An open-source, free statistical analysis environment. We use R here for graphic analysis of pixel colors to find thresholds. R is widely used for all kinds of analytical projects.
• CIMG: a free library for C++ that allows images to be manipulated as 3 matrices of color values - one each for red, green, and blue.