A method and apparatus are provided for identifying differences between a stored
pattern and a matching image subset, where variations in pattern position, orientation,
and size do not give rise to false differences. The invention is also a system
for analyzing an object image with respect to a model pattern so as to detect flaws
in the object image. The system includes extracting pattern features from the model
pattern; generating a vector-valued function using the pattern features to provide
a pattern field; extracting image features from the object image; evaluating each
image feature, using the pattern field and an n-dimensional transformation that
associates image features with pattern features, so as to determine at least one
associated feature characteristic; and using at least one feature characteristic
to identify at least one flaw in the object image. The invention can find at least
two distinct kinds of flaws: missing features, and extra features. The invention
provides pattern inspection that is faster and more accurate than any known prior
art method by using a stored pattern that represents an ideal example of the object
to be found and inspected, and that can be translated, rotated, and scaled to arbitrary
precision much faster than digital image re-sampling, and without pixel grid quantization
errors. Furthermore, since the invention does not use digital image re-sampling,
there are no pixel quantization errors to cause false differences between the pattern
and image that can limit inspection performance.