Correlating Image Principle
Working principle is based on image registration of surface moving object. Schematically device is shown on fig.1. Digital optical camera is a essential part of device and consists of objective, line scan CCD matrix and electronic unit. Objective forms on CCD matrix an image from object surface. This image reads and then digitized. In fact, this is analogous to common digital camera.
Fig.1. Object surface digital image.
The method of registration of moving surface is follows. Continually optical camera gets a set of moving surface digital images. To develop an object moving it is needed to compare two images, getting optical camera between time interval Δt. In case when object is not moving the differences between two images are minimal. If an object is moving, some regions in current image are shifted in comparison with previous image. To compare two images, current and previous, it is possible to get the image displacement on CCD matrix. On fig.2 are shown two images: previous and current.
Fig.2. Two moving object images: previous and current.
To compare two images are used the well-known correlating analysis technique. In the first line image pixel window with width N are chosen. And in second line image pixel window with width N are chosen also, but shifted on some pixel value n. The dependence correlating function K(n) on shift n is calculated with well-known formula. Fig.3 shows dependence correlating function K(n) for two images, those are shown on fig.2.
Fig.3. Correlating function for two image sequence.
The correlating function K(n) position maximum defines shift Δp between two images. To get a real object displacement ΔL it is needed to take into account distance D to the object. If the distance D is known it is not difficult to get real object velocity V.
Last modified: марта 28, 2016