Among the apparently simplest methods to determine bubble size in flotation systems are photographic techniques, ranging from photography through transparent walls to imaging of extracted bubbles. All capture images, which to varying degrees include overlapping, touching or out of focus bubbles. As manual counting limits the total number of bubbles, image analysis software is used to automate the process. Accuracy is thus dependent on image treatment, including counting method and filters. The McGill bubble size analysis method yields single plane, backlit images and utilises software that filters by shape factor. Proven effective for bubble size distributions ranging from approximately 0.5 to 3 mm, regular trends are observed when number (D10) and Sauter (D32) mean diameters are compared. When the method was extended to wide distributions typical of jetting spargers (e.g., 0.2--15 mm), no similar trends were evident. Revision of the analysis process for these two-phase systems included counting by number of holes, which reduced dependence on bubble shape. This allowed for inclusion of small and large bubbles, while excluding bubble clusters. A diameter assignment protocol reflecting individual bubble shape was also developed. Revised output distributions showed increased symmetry, and the D32 vs. D10 trend was recovered. Impact of sample tube diameter on the output bubble size distributions, and types of bias introduced were also investigated. A means of selecting an appropriate sample tube diameter for a given bubble population is presented.

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