A segmentation approach for touching char particles

Separation of touching char particles is required for measuring morphological characteristics. In this paper, a segmentation approach for touching char particles is presented. The proposed approach is fourfold. Firstly, contours are extracted. Secondly, concave points are identified by the means of measuring concavity using gradient directions at contour points. Concave points are candidates of touching point. Thirdly, separation lines are identified using location, length, blur and area. Fourthly, a decision criterion is derived for deciding whether to split a particle or not. Coal samples, from three Colombian regions (Antioquia, Cundinamarca, and Valle) and blend coals 50%-50% were devolatilised and chars were obtained. The proposed approach was evaluated using 180 images of char particles and compared to the Watershed algorithm. The evaluation was twofold: quantifying the accuracy in identifying touching particles and measuring the separation quality. An expert criterion was used, as a ground truth, for qualitative evaluations. A good agreement between the visual judgement and automatic results was obtained, using the proposed approach.