Figure 4.

Imaging and segmentation of GFP containing chromatophore system. (a) Close-up of a three-dimensional rendering of the Favites abita polyp shown in figure 1e. Highest OCT signal intensity (in red) reveals chromatophores. Length of arrows equals 500 μm. (b) Cross-sectional OCT B-scan through the polyp mouth. Chromatophore visualization (in white) was enhanced through narrowing the threshold of the OCT signal. Dotted black lines show examples of maximum chromatophore diameter. Scale bar, 100 µm (c). Top view of three-dimensional rendering of coral polyp in false colour mode and (d) in black and white colour mode. Scale bar, 500 µm. Regions of interest (labelled 1–3) of 1 mm² quadrats were selected for chromatophore analysis. (e–h) Example of segmentation steps to yield physical characteristics of chromatophores. (e) Close-up of region of interest 2, (f) brightness and contrast adjusted image, (g) binarized image using the Otsu algorithm and (d) detected particles (see Material and methods for details).