Example of the masking process. Top left panel: pre-calibrated frame, without flat field correction. Top right panel: pre-calibrated frame, with flat field correction applied. Bottom left panel: masked frame without flat field correction. Bottom right panel: flat field corrected frame with Gaussian smoothing. Notice that NoiseChisel (Akhlaghi & Ichikawa 2015) efficiently detects objects with very different shapes and sizes, masking the outskirts and diffuse regions that are barely visible even in the convolved frame.