Estimating vegetation coverage in wheat using digital images

Abstract

No method exists to reliably predict percent vegetation coverage using indirect measures. This study was conducted to evaluate the use of digital image processing techniques applied to digital color, red‐green‐blue (RGB), images of crop canopies to estimate percent vegetation coverage and biomass. Two field experiments with winter wheat (Triticum aestivum L.) “Tonkawa”; were planted in October 1996 and 1997 at Perkins, OK on a Teller sandy loam (Udic Argiustoll) and at Tipton, OK on a Tipton silt loam (Pachic Argiustoll). Plot images from winter wheat canopies were taken using a Kodak DC40 Digital Camera (1995)¹ with an image resolution of 756 × 504 pixels. Spectral irradiance readings were taken from wheat canopies in red (671±6 nm) and near infrared (780±6 nm) wavelengths, and normalized difference vegetation index (NDVI) was calculated. Percent vegetation coverage was estimated using image‐processing routines in Micrografx Picture Publisher® version 7.0. The digital images were converted from 8‐bit RGB tagged image file format (TIFF) files, which were produced by processing the images from the camera with Photo Enhancer®, to binary pseudo‐color images. Percent of pixels corresponding to the vegetation color was then calculated and used as the percent coverage for each plot. Binary pseudo‐color images provided useful estimates of percent vegetation coverage that were highly correlated with wheat canopy NDVI measurements.