A novel subpixel edge detection system for dimension measurement and object localization using an analogue-based approach

Abstract

This paper describes an analogue-based approach to subpixel-level edge detection for dimension measurement and object localization. Although the most common subpixel edge detection methods employ digital-based approaches, at present they show certain drawbacks such as the difficulty of real-time, in-line subpixel edge detection, the necessity of implementing expensive high-resolution A/D converters, and difficulty in performing continuous, dynamic subpixel edge detection. These drawbacks present a difficult problem in digital-based systems industrial applications. We propose a new analogue-based first derivative subpixel edge detection approach to overcome these drawbacks. Our method involves the approximation of the distribution curve of the first derivative of the output of a CCD by using the second-order polynomial, and thus can accurately detect a peak position of the differential curve by means of the interpolating calculation, the operation of which is realized primarily through the use of analogue circuitry. The measurements of a concrete form using the prototype system demonstrate that its resolution under ideal conditions is about 1×10-1 pixels. While the resolution of this system decreases in an actual situation, the resolution remains at an acceptable subpixel level. We thereby conclude that the approach described in this paper is effective for real-time, low cost edge detection.