Linear (panel a) and non-linear (panel b) camera responses to a set of six achromatic samples from an X-Rite Colour Checker Passport corresponding to the green channel of a Canon 40D camera.

<p>The six achromatic samples uniformly reflect, from bottom to top, 3.10%, 9.11%, 19.5%, 37.2%, 60.9% and 94.8% of incident visible irradiation <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0096646#pone.0096646-Myers1" target="_blank">[47]</a>. Camera responses correspond to an area of 900 pixels² located at the centre of each grey swatch. Error bars along the <i>x</i>-axis represent pixel intensity variation within the sampling square, whilst error bars along the <i>y</i>-axis represent variation within recovered linear values arising from the uncertainty associated with the use of a biexponential linearisation equation <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0096646#pone.0096646-Garcia1" target="_blank">[31]</a>. Error bars represent standard deviation in both cases. P-value significant at ; NS P-value not significant at .