subset meaningful to illustrate the capabilities of VSS. Figure \[fig:perceptual\_enhancement\] shows the results of the perceptual enhancements using color-coding and iso-lines as well as their combination.

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**Color-coding depth.** Color and brightness are commonly used to communicate depth in vessel visualization [@Ropinski2006; @Borkin2011; @Kersten2014]. For our visualization we utilize the chromadepth and pseudo-chromadepth techniques, which exploit the effect that shorter wave lengths are refracted more than longer ones at the lens of the eye, and thus create the illusion of depth in 2D images. The full chromadepth range contains more than two colors which have no order beside their corresponding wavelength, which can be confusing for users. Especially colors such as yellow appear brighter compared to red and can therefore wrongly be perceived closer. The reduction to pseudo-chromadepth with blue (far) and red (close) has the advantage that no confusion between the mental mapping from color to depth is occurring. Alternatively, the dark-means-deep metaphor can be utilized if depth values are mapped to black (far) and white (close) as monochromatic color scale. This supports people with any sort of color blindness while still being expressive for everyone. We apply the used colormap solely to the VSS to 