This paper presents a real-time image analysis system that was installed at a phosphorus oxide flotation process. The focus of the image analysis system is to effectively estimate bubble size. Flotation is one of the most challenging processes for modelling and control in mineral processing industry due to the inherently chaotic nature of the underlying microscopic phenomena and the lack of sufficiently accurate process measurements. Digital image processing is a promising technology for obtaining process related information that call potentially be used to improve the control of flotation processes. Traditional bubble size estimation techniques based oil morphological operators and the concept of texture spectrum perform unsatisfactorily on froth images from the phosphorus oxide flotation process. A modified texture spectrum approach and a method based on binary images are proposed and implemented. The reliability of the proposed bubble size estimation approach is demonstrated on phosphorus oxide flotation processes. (C) 2007 Elsevier Ltd. All rights reserved.