  This paper presents a novel setup for automatic visual inspection of cracks
in ceramic tile as well as studies the effect of various classifiers and
height-varying illumination conditions for this task. The intuition behind this
setup is that cracks can be better visualized under specific lighting
conditions than others. Our setup, which is designed for field work with
constraints in its maximum dimensions, can acquire images for crack detection
with multiple lighting conditions using the illumination sources placed at
multiple heights. Crack detection is then performed by classifying patches
extracted from the acquired images in a sliding window fashion. We study the
effect of lights placed at various heights by training classifiers both on
customized as well as state-of-the-art architectures and evaluate their
performance both at patch-level and image-level, demonstrating the
effectiveness of our setup. More importantly, ours is the first study that
demonstrates how height-varying illumination conditions can affect crack
detection with the use of existing state-of-the-art classifiers. We provide an
insight about the illumination conditions that can help in improving crack
detection in a challenging real-world industrial environment.
