Digital image processing device and method for holistic evaluation of subtle irregularities in a digital image by using the scale space technique to identify irregularities of interest and by calculating a total irregularity score using a function of intensity, scale and optionally location of the identified irregularities of interest. Specifically, the digital image represents a liquid mixture formed by mixing two or more liquid compositions of different ingredients, colors, viscosities, and/or solubility; the subtle irregularities represent non-homogenous mixing spots or regions in such liquid mixture.