# Non-Contact Dermatoscope with Ultra-Bright Light Source and Liquid Lens-Based Autofocus Function
## 4 Discussion  
The non-contact dermatoscope presented in this work features both an integrated autofocus function calibrated by using an infrared laser-based distance sensor as well as image post-processing. The large working distance is beneficial for routine examinations. If in a future version of the system the distance sensor will be aligned along the optical axis of the camera via a dichroitic mirror, for example, it will be able to focus over an even larger range. Also, a distance-variable image scale would be advantageous and can be included in our system. Furthermore, a color read out tool could be added to the software. With this tool, images taken during different examinations could more easily be compared which could provide, for example, additional information about the blood perfusion. Also, use in therapy monitoring is possible.  
The color calibration of our system is not yet optimal as the color values in the calibrated image still deviate from the reference color values. The uncalibrated image is comparably dark. This is because the gain of the camera was set to zero, so that the images can more easily be compared after image noise reduction. Also, the exposure time was set to 75 ms as a compromise between image brightness and exposure time to avoid motion blur. An even brighter light source would be advantageous in this regard. Another option would be to track the gain for the images taken and include this value in the calibration algorithm.  
With regard to CRI requirements, halogen light sources and high pressure xenon lamps, for example, can have CRI values of 100 and 93, respectively [24]. As we use an LED with a more discrete emission spectrum, the CRI cannot directly be compared with CRI of the more continuously emitting light sources mentioned above. The reason for this is, that small changes in a discrete spectrum can result in large changes in the CRI which does not correlate with the changes in color representation as perceived by an human observer or a camera [25]. Also, the spectral acceptance of the sensor employed, i.e., the camera system, has to be taken into account. As even the light situation in examination rooms can alter because of, for example, the daytime, no exact color matching is needed in this case. It is more important to ensure comparable colors in every picture taken by the system. The light source and image algorithms can further be improved by spectral tuning to enhance visibility of different features relevant for diagnostics in dermatology [26].  
Finally, the hardware components of the system can be made more compact, so that the it can serve as a module in an automated skin-screening device. In such a scheme the patient lies on a medical lounger and an automated arm equipped with suitable imaging systems takes overview pictures of the skin and identifies nevi and other areas relevant to dermatology. Subsequently, the system described in this work would take high-resolution images of the selected skin areas. In case of nevi, an algorithm that evaluates the ABCDE criteria could then make a risk analysis so that the physician only needs to examine the suspicious ones in more detail. In further versions, external image analysis from outside the examination room could be implemented as well as deep learning approaches for fast and essentially real-time analysis as pointed out in [27].