1. A method comprising: sampling pixels within first and second component regions of a tool impression in a digital image; determining for each of the first and second component regions respectively a distribution using a processing unit, each of the resulting first and second distributions relating to a pixel property of the sampled pixels within the respective first and second component regions; computing an adjustment factor based on the distribution of the pixel property using the processing unit, based upon both the first and second distributions; receiving a predetermined parameter that is independent of both the first and second distributions of the pixel property; computing an assisted tolerance parameter based on the adjustment factor and the predetermined parameter using the processing unit; specifying a first edit class of a plurality of edit classes based upon the predetermined parameter and the assisted tolerance parameter, wherein each edit class defines one or more respective subsets of the distribution; determining for each pixel within the first edit class of the plurality of edit classes a weighting using the processing unit; and collectively editing using the processing unit the subset of sampled pixels that correspond to one of the subsets of the distribution defined by the first edit class by applying a first edit operation to each pixel in the subset of the sampled pixels using the processing unit, the first edit operation for each pixel being determined in dependence upon at least the determined weighting for that pixel, the predetermined parameter and the assisted tolerance parameter.