Colour makes it easy

Sensor Review

ISSN: 0260-2288

Article publication date: 1 March 2000



Loughlin, C. (2000), "Colour makes it easy", Sensor Review, Vol. 20 No. 1.



Emerald Group Publishing Limited

Copyright © 2000, MCB UP Limited

Colour makes it easy

"Colour makes it easy" was a figure caption in a paperI published about 16 years ago. The figure was actually two photographs, one in black and white and the other in colour of the same scene which featured a snooker(pool) table and a Steve Davis look alike. The theme of that paper was that the difficulty of a particular problem (e.g. locating a red ball) depends very much on how you look at it.

In the above almost trivial example, locating the red ball with any degree of certainty using a black and white CCD camera was impossible as its particular shade of grey was indistinguishable from that of a number of other balls of very different colours. Change to a colour camera and it is suddenly quite difficult not to identify the red ball. Of course instead of changing cameras we could have changed the colour of the illumination and achieved a similar effect. The point is that a simple change in hardware was actually more effective in terms of achieving the objective than any number of hours spent on software development.

If you are only concerned with gross colour differences and where the object stands out conveniently from it surroundings (green baize), then correct selection of camera and/or lighting are likely to take you a long way towards a solution. However if you are looking for fine colour discrimination or comparing against absolute colour references, then a much more thorough understanding of colour, lighting reflectance, camera response and the human eye are required.

Fortunately this issue includes contributions that cover all these areas in considerable depth and breadth.

"Colour makes it easy" is perhaps a trifle optimistic and it would be more accurate to state "Colour makes it easier". However despite benefits that colour can provide it is still relatively uncommon to find colour vision systems being applied in industry where grey scale dominates.This is something that I expect to change quite soon. I have been expecting it to change quite soon for 16 years so my powers of prophecy may be questionable, but the technology available today makes the use of colour much easier.

However just because the technology is now available we must be careful not to lose sight of the original message. To give another example I once needed to detect the presence of a clear plastic sheet. Various options concerning angles of incidence and reflection were considered but the nature of the process made these difficult to implement. Almost by chance we discovered that placing a light source with a linearly polarised filter on one side of the sheet and a light sensor with a similarly aligned filter on the other solved the problem. Without the clear plastic sheet present the light from the source passed through to the sensor unhindered, but as the plastic had the effect of rotating the plane of polarisationof the light, it acted as a simple but very effective optical switch.

Success in any given project seems to rely on achieving the correct balance between rigorous analysis, excellence in execution and an open mind.

Clive Loughlin

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