Vision Systems

Image Acquisition
The first stage of any vision system is the image acquisition stage.

After the image has been obtained, various methods of processing can be applied to the image to perform the many different vision tasks required today.

However, if the image has not been acquired satisfactorily then the intended tasks may not be achievable, even with the aid of some form of image enhancement

2D Image Input

The basic two-dimensional image is a monochrome (greyscale) image which has been digitised.

Describe image as a two-dimensional light intensity function f(x,y) where x and y are spatial coordinates and the value of f at any point (x, y) is proportional to the brightness or grey value of the image at that point.

A digitised image is one where

• spatial and greyscale values have been made discrete.
• intensity measured across a regularly spaced grid in x and y directions
• intensities sampled to 8 bits (256 values)

For computational purposes, we may think of a digital image as a two-dimensional array where x and y index an image point. Each element in the array is called a pixel (picture element)

2D Input Devices
TV Camera or Vidicon Tube

A first choice for a two-dimensional image input device may be a television camera -- output is a video signal:

• Image focused onto a photoconductive target.
• Target scanned line by line horizontally by an electron beam
• Electric current produces as the beam passes over target.
• Current proportional to the intensity of light at each point.
• Tap current to give a video signal.

This form of device has several disadvantages.

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