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March, 2019


Optimizing Digital Inspection by Understanding Lighting and Illumination


By Alistair Gooch, Marketing Manager, Inspectis AB


relies on illumination, and more specifically, the quality and intensity of lighting. The benchmark has always been the human eye, directly or under magnification. As wonderful and powerful as the eye is, however, today’s digital camera microscopes are far more powerful, in terms of sensitivity, resolution and other qualities and characteristics. They are immensely capable


V


and adaptable and can be tuned to provide amazing detail in low light,


etc., but again, light — illumination — is king. Whether it be the eye or a camera, we can only observe an object in visible light based on the amount of light reflected back from the object under scrutiny.


Assisted Human Vision To get the very most out of the


broad capabilities of today’s digital microscopes, the illuminating light that is provided by a source, whether it be a bulb or an LED, must be tuned to optimize these capabilities. This includes the intensity, wavelength, color, direction, and more. In this way, defects or features


that might otherwise go undetected will be seen before a defective part moves downstream. Since this is not machine vision, but rather assisted


High-quality cameras, optimum lighting and large-area, high-resolution displays are key elements for proper inspection.


without optimized control of that lighting. This does not mean that the lighting or illumination needs to be particularly intense or especially bright, but rather, controlled or tuned in such a way that the cam- era’s best qualities and capabilities are optimized to sense it. Camera and illumination must work together to provide the best possible image to the human inspector.


To get the very most out of the broad capabilities


of today’s digital microscopes, the illuminating light that is provided by a source, must be tuned for intensity, wavelength, color, direction, and more.


human vision, the digital microscope must provide the optimum image quality and magnification to assist the human eye and the operator in seeing what they need to see. But even the finest digital cam- era technology cannot achieve this


There are a number of ways to


achieve this, including varying the type of light, wavelength and intensi- ty, color, proximity to the camera, angle of view, positioning of the sources of illumination, filtering, dif- fusing, or polarizing the light, and


other variables, some of which can be controlled by system software. There are multiple ways to pro-


vide illumination, with the goal of revealing different things, e.g., tex- ture, detail, form, color, and more. With video microscope inspection, for example, the quality of light used can dramatically change the way the subject is seen on the monitor. With today’s video microscope


systems, powerful software packages provide camera and lens adjustment and control, setup presets, saved recipes, automatic calibration, track- ing for zoom positions, and automat- ic lens distortion correction for cap- tured images, as well as automatic and manual focus stacking.


Light and Surfaces It is important to understand


how the different forms of lighting interact with various surfaces. It is also important to understand the dif-


isual inspection of anything — products, parts, PCB assem- blies, or medical devices —


ferent forms of light and various light- ing techniques. When searching for or specifying the components of an inspection system, first ask, simply, “What specifically (or primarily) do I want this inspection system to do?” Are we looking for a defect in a


part, or do we need to measure a part’s dimensions, or just determine the presence or absence of a feature? Then we must decide upon the opti- cal components that make up the inspection system. Indeed, it may seem a stretch,


but the part that we want to inspect is in itself an optical component because it reflects or scatters light and helps form an image in the cam- era. In fact, it is the most important optical component, because it has the greatest effect on the light in the inspection system. Therefore, we must take into account the part’s optical properties, such as its surface reflectivity, its geometry, and even


Ring lights that encircle the camera lens are a commonly used form of illumination for inspection.


its color to devise lighting that works properly. The surface or surfaces of a part


Continued on page 61


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