Image preprocessing method for detecting an abnormality

A device for monitoring a spread front using a spread camera to detect an abnormality, the device comprising:

• a spread image camera to generate a series of images of interference fringes formed by reflections off a superstrate and a substrate as the superstrate conforms to the substrate while forming a film;
• one or more computer-readable storage media;
• and
• one or more processors that are in communication with the one or more computer-readable storage media and that cooperate with the one or more computer-readable storage media to cause the device to perform operations comprising:
• extracting an annular set of pixels that form an annular shape including one or more of the interference fringes for each image in the series of images;
• converting each of the annular set of pixels into one or more rectangular sets of pixels of a rectangular shape;
• detecting a probability of an abnormality in any of the one or more rectangular sets of pixels;
• and
• reporting the probability.