Dimensional Measurement using Vision Systems - NPL Publications ...

Measurement Good Practice Guide No. 39
1.2.2 Image processing
Once the object of interest has been imaged correctly, measurements can be made. For this,
some form of computer or microprocessor is required to process the image detected by the
camera. A frame grabber, controlled by proprietary vision system software, is normally
used to read the digitised image from the camera. Once the image is captured, it can be
processed, with measurements being made using functions and algorithms in the vision
system software.
1.2.3 Communication
The final process is to communicate the results of the measurements to the operator. The
most common and simplest method is to graphically display the image and any
measurements performed, on a monitor. However, this is generally not sufficient for
vision systems that are integrated into a manufacturing process. With these systems it may
be necessary to output the measurements to other devices, such as PLC’s (Programmable
Logic Controllers), which are used for in-process control, or to file storage devices, so that
the information can be retrieved for use at a later time. The ability to provide real time
feedback into a process is one of the main advantages of vision systems.
In configuring a vision system there are many different combinations of image formation,
sensing and processing components and techniques available. Each system is therefore
likely to have unique components to perform the task required of it. The following
sections will describe the more common methods and devices used by vision systems to
achieve these three key processes.
2 MICROSCOPY
Vision systems designed for measuring microscopic* objects are likely to use an optical
microscope or similar high-powered lens arrangement. In order to make accurate
dimensional measurements with such equipment it is advantageous to have an
understanding of not only how the microscope produces an image, but also of the
associated illumination equipment and the limitations to the measurement caused by the
nature of light. *Note - for the purposes of this guide, objects less than 1 mm in size will be classed
as microscopic and objects greater than 1 mm, macroscopic.
The following sections, which are taken from the NPL Course: Optical Microscopy for
Dimensional Measurement in Microelectronics, consider these issues in detail.
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