The WOP is mainly used to investigate trends in structural anisotropy yet interpreting the data must be done carefully. As seen in Fig. , the WOP values within a single image can cover a wide range, representing either monomodal or multimodal distributions. As such a simple mean ± error WOP value is often not adequate to describe the system. In multimodal systems, a density plot (Fig. ) can be used to visualise the distribution of WOP values. The wide range of WOP values seen in Fig. , down to -0.8, is caused by transition regions, which arise either via low signal-to-noise ratios or the presence of high contrast, caused, e.g., by abrupt transitions from protein to water or crystalline cellulose (Fig. or Fig. ) or air bubbles present in MRI images (Fig. ). Absolute differences in WOP values can be explained by presence of these transition regions at the different length scales. CLSM images contain these high-contrast transition regions to a greater degree due to their presence at the μm length-scale and thus have a lower average WOP compared to MRI images.