Table 2. Feature Definition.
| Feature | Definition |
| Global | |
| intensity | Average of the absolute deviation of each pixel intensity from the mean pixel intensity. |
| mean | Average pixel intensity. |
| med | Median pixel intensity. |
| std | Standard deviation of the pixel intensity. |
| mad | Median absolute standard deviation of the pixel intensity distribution. |
| Etot | Total entropy. |
| Emean | Average of the local entropy. |
| Emed | Median of the local entropy. |
| Estd | Standard deviation of the local entropy. |
| aiqr | Inter quartile range of the pixel intensity distribution. |
| aq68 | Width of the central  % quantile of the pixel intensity distribution. |
| aq95 | Width of the central  % quantile of the pixel intensity distribution. |
| ROI dependent | |
| segment | Area of the pixels determined to be ROI. |
| segmentConv | Area of the pixels after applying a convex hull covering to each segmented region. |
| skeleton | Total length of skeletonized ROI. |
| skeletonBranch | Number of branching points of skeleton. |
| skeletonEnd | Number of endpoints of skeleton. |
| endpoints | Endpoints of ROI image. |
| Euler | Euler number of image. |
| caSum | Total convex hull covering area summed over all segments (can become larger than  due to overlapping). |
| faSum | Total area of pixels within all segments after filled in holes. |
| numObj | Number of identified segments. |
| Per segment ROI dependent, summarized by mean and standard deviation | |
| solidity | Ratio of the filled area (with holes closed) and the convex hull area. |
| caRel | Convex hull covering area of the segment in percent of the segment size. |
| faRel | Area of pixels in the segment after filling in holes in percent of the segment size. |
| ecc | Eccentricity of a fitted ellipsoid covering the segment. |
| ext | Extent of the filled area of the segment. |
Initial feature set considered for image analysis. The per segment calculated image features are summarized for each image by their mean and standard deviation. All image features that measure an area are recorded in percent of the total number of pixels. Pixel intensity related image features are given in percent of the maximal pixel intensity. For applied transformations see Material and Methods.