Fig. 3

Spectral image processing workflow of a reference cross-section. a Images were acquired in 10 angle increments from β = 0 to 360°, aligned, and used to calculate a surface normal vector map. Using this normal map, gradients were calculated for every illumination angle and then used to normalize the input images. b From the surface shape corrected image set, an average projection (darkfield equivalent), minimum projection (focal plane diffuse scattering only), and max–min (extraneous additional scatter) images were created. c Detail of the average image shows blur in the 1–10 µm range, but the minimum image d displays pigment particles with resolvable features below 1 µm. e The schematic diagram represents the overlap of two scattering paths which is explained in more detail in the text below. The minimum projection provides a measure of the overlap between the scattering regions (gray region)