Quality assessment of agricultural products has been the subject of numerous reviews; however, not many papers address internal visualization as a means of quality grading. This paper reviews established as well as emerging visualization techniques utilized in the quality assessment of food products. In this discourse, the authors set out to underscore some of the most novel signal processing techniques employed in the non-destructive grading of agricultural products by way of an automated quality verification system. Such systems utilize advanced engineering principles with imaging, signal processing as well as color differentiation to accomplish the grading task. The materials presented will be useful to agricultural engineers, manufacturing engineers, food engineers and any other researchers in the food and agriculture industries. (C) 2013 Elsevier Ltd. All rights reserved.