Within Food R&D scientists, chefs and engineers aim to develop natural fruit and vegetable based soups with optimal flavour, texture, appearance and health benefits whilst maintaining product safety. The colour and appearance has a major influence on the perceived quality (e.g. nutrition and freshness). This paper describes a method for the determination of the colour of soups containing vegetable particles. Digital images were made under controlled lighting using a DigiEye imaging system. It allows documenting the appearance by making colorimetrically accurate images which are suitable for the measurement of colour uniformity, size and shape. The uniformity of the light under diffuse and directional illumination was investigated using different targets and soup samples. For accurate colour analysis the images have to be corrected for non-uniform illumination and the colour has to be measured at a fixed location outside the centre of the lighting cabinet. Directional illumination (angled light with additional mirrors) was used to introduce gloss resulting in images matching the actual appearance of soups and vegetable particles very closely. Imaging glossy soups under diffuse illumination resulted in dull images with dark spots. No significant difference was found between the colours of soups analysed under diffuse or directional illumination. Under directional illumination a better repeatability was observed. Additionally, for 36 different soups, the measured results from the DigiEye system were compared to two different colorimeters (0°/45° and diffuse/0° geometry). Linear relations were found between the CIE Lab values measured by the DigiEye system and those measured by two different colorimeters. Best correlations were obtained between DigiEye and 0°/45° colorimeter (r2=0.980-0.996). The short term precision of the DigiEye system is somewhat better than those of the colorimeter.
Gerard van Dalen, Faisal Osman, Aat Don, "Colour and appearance analysis of fruit and vegetable soup using a digital colour imaging system" in Proc. IS&T CGIV 2010/MCS'10 5th European Conf. on Colour in Graphics, Imaging, and Vision 12th Int'l Symp. on Multispectral Colour Science, 2010, pp 399 - 406, https://doi.org/10.2352/CGIV.2010.5.1.art00063