Towards standardized wound imaging: Self-calibrating consumer hardware based on lattice detection on color reference cards

Photographic documentation in medicine is of increasing importance. Efficient methods are required to properly register and calibrate the images. Usually, a standard reference card with special color pattern is placed in the aperature of the image. Localization and extraction of such cards is a critical step. In this paper, we adopt an iterative lattice detection algorithm developed for outdoor images. Once the lattice is extracted, crossing points of the color fields are used for perspective geometric transform while the color plates guide the color calibration process. Our method is tested on 37 images collected within the German Calciphylaxis Registry. At least, 28 out of the 35 possible grid points have been extracted in all the non-standardizes photographs, with at most two false positive detections. The lowest F-measure was above 80%. Hence, ruler and other calibration devices become obsolete and wound imaging can be performed with low-cost hardware, too.