Calculated plant pixel area (average of 18 consecutive silhouettes differing by 10°) as a function of measured plant leaf area at different scanning speeds in rapeseed. Values in each panel indicate an increasing scanning speed during measurement and are plotted with a different symbol colour. A Scanning speed 0.9, 1.8, 3.6 m min−1. B Scanning speed 5.4, 9.0, 12.6 m min−1. C Scanning speed 16.2, 19.8, 23.4 m min−1. Correlation coefficients ranged between 0.9589 and 0.9865 (slopes all significant at P < 0.0001). Leaf area ranged between 64 and 350 cm2 (n = 15).