Calculated plant pixel area (A) and calculated max height (base to the highest leaf tip; B) versus measured values in four species (maize, blue; barley, red; tomato, purple; rapeseed, green). Correlation coefficients for all species ranged between 0.9542 and 0.9925 (P < 0.0001). For maximum height a single regression model was highly significant (P < 0.0001). For leaf area the slope of a single regression model is significant for monocyledonous species (P < 0.0001) but not for dicotyledonous ones (P = 0.34). The dashed line depicts the 1:1 relationship. Measurements were conducted at a constant scanning speed of 0.9 m min−1.