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Figure 5. (a) Representative slice of micro-CT data through a sample of Porites lutea (FRH49) showing denser structure as brighter grey to white values and less dense structure, such as air, as dark grey to black values surrounding the specimen. Black scale bar = 10 mm. (b) Same slice segmented into three phases: skeletal material (shaded yellow); organic matrix (shaded purple); and air/bubble wrap within and surrounding the specimen (unshaded black). (c) Grayscale histogram of 16-bit micro-CT data showing the points of segmentation between the different phases. The two peaks within the lowest density phase represent the air within and surrounding the specimen (peak around 12000) and bubble wrap and plastic specimen holder (peak around 17000). (d) Difference between the 20 micrometer and 10 micrometer data trends highlighting the very small variability within the porosity trends with no consistent trend towards an under- or over-estimate of porosity at one given resolution. (e) Plots of skeletal volume trends within the x-y cross section of a 12x12x12 mm³ ROI as a function of distance along the z-axis of the ROI for both 20 micrometer and 10 micrometer micro-CT data. (f) Representative slice (at 4.3 mm) from P. lutea sample comparing the 20 micrometer to 10 micrometer micro-CT data (left hand figures) and segmented skeleton in both (right hand figures). White scale bar = 6mm. (g) Box plots showing the variability of porosity within and across coral species.