Subpixel measurements using a moment-based edge operator

Recent results in precision measurements using computer vision are presented. An edge operator based on two-dimensional spatial moments is given. The operator can be implemented for virtually any size of window and has been shown to locate edges in digitized images to a twentieth of a pixel. This accuracy is unaffected by additive or multiplicative changes to the data values. The precision is achieved by correcting for many of the deterministic errors caused by nonideal edge profiles using a lookup table to correct the original estimates of edge orientation and location. This table is generated using a synthesized edge which is located at various subpixel locations and various orientations. The operator is extended to accommodate nonideal edge profiles and rectangularly sampled pixels. The technique is applied to the measurement of imaged machined metal parts. Theoretical and experimental noise analyses show that the operator has relatively small bias in the presence of noise