Fig. 5

Quadratic fits over a day with a constant change in illumination and b step-changes in illumination. Graphs displaying the \(R^2\) value of a linear fit, (dashed lines) and quadratic fit (solid lines) for the red, green and blue channels of the colour checker tiles. The 60 wheat plots in the experiment are ordered by illumination i.e. the difference between observed and reference colour checker values, shown on the left-hand side y-axis and represented by the black dashed line