1. A focus assessment method for determining a focus classification for a workpiece feature image, the focus classification usable to determine whether the image is sufficiently focused, such that a machine vision inspection system may perform useful machine vision inspection operations on the workpiece feature image, the method comprising: using the machine vision inspection system to perform the steps comprising: (a) acquiring a first image of a workpiece feature for which an image focus classification is to be determined; (b) determining a plurality of focus classification features based on the first image, the focus classification features being abstract features included in a multi-parameter feature vector; and (c) determining the focus classification based on processing the determined plurality of focus classification features using at least one classifier, wherein: the at least one classifier comprises at least a first respective classifier that operates on a first respective plurality of classification features; the focus assessment method does not require the acquisition of an additional image of the workpiece feature that is differently focused than the first image; at least the first respective classifier is trained on at least a first respective set of training images; the set of training images comprises respective images of a plurality of different workpieces, wherein the respective images include in-focus images and out-of-focus images; and the respective images are assigned a respective desired focus classification prior to training the respective classifier.