Print image registration is the key technology for achieving automatic inspection of print quality.According to print image with high resolution

original image is segmented into multiple regions of interest

center coordinates and rotation angle are treated as parameters of image registration

and the minimum rotation angle between inspected image and temple image is determined by variable step searching algorithm; an affine transformation is implemented on the inspected image and the bidirectional subtraction image between inspected image and temple image is calculated; defect is recognized by binary threshold and defect region area threshold.Experimental results indicate that the detection accuracy of the inspection system is up to 96 % for qualified products

and 94 % for unqualified products.