Comparing Image Format and Resolution for Assessment of Foliar Diseases of Wheat

Abstract

For image analysis to be a useful method for assessment of foliar diseases, it must be robust with respect to changes in image resolution. In addition, the use of common compression methods such as JPEG allows for the use of low-cost digital cameras and reduces the storage requirements of the imagery. We have investigated the effect of image resolution and format on lesion area quantification with image analysis. Wheat leaves with various levels of rust and tan-spot were scanned on a flatbed scanner as TIFF images with a resolution of 8.4 million pixels per image. These images were then progressively reduced in resolution down to 858 pixels per image. The TIFF images were then converted to JPEG images with quality settings of 100, 75, 50, and 25 percent. The percentage of necrotic leaf area was then measured for each image, and correlated with the percentage of necrotic leaf area of the original 8.4 million pixel TIFF images. Image format had little effect on the results and image resolution did not affect results until the image resolution had dropped below the level at which it was difficult to discern lesions by eye. This suggests that low-resolution digital cameras with high JPEG compression levels are suitable for plant disease measurement using image analysis. Accepted for publication 21 April 2005. Published 16 May 2005.