Figure 6

Using digital image filters to increase the quality of volume rendering from paraffin wax sections. (a) Unfiltered image stack of Phoronis australis sections: detail of a single slide from the unfiltered green channel. (b) First filtering step: detail of a single slide from the green channel after applying the Amira 3D Gauss filter (6 × 6 × 6 kernel, sigma = 1, 1, 1). (c) Second filtering step: detail of a single slide from the green channel after applying the Amira 3D edge-preserving-smoothing filter (contrast = 3.5, sigma = 3, step = 5, stop = 25) on the previously already Gauss-filtered stack. (d) Slide from the unfiltered RGBA stack. (e) Slide from the filtered RGBA stack after applying the two aforementioned filters (a-c). Note that structures as small as single blood cells remain to be distinguishable after both filtering steps (red arrows). (f) Volume rendering based on the unfiltered RGBA stack. Through the high level of very fine-scale detail, perception of the 3D structures is more difficult. (g) Volume rendering based on the filtered RGBA stack. Besides balancing geometric distortions, image filters decrease the amount of very fine-scale information and thus significantly ease perception of 3D structures.