Influenced by what we see

One happening or remark often makes us notice others that would previously have passed us by. This was the case with the final paragraph of my last column, which referred to colour schemes for displaying data. As it was landing on your doormat, there were two events with connections to the wider use of colour in nature and art. The first was the broadcast of the two-part series Attenborough’s Life in Colour on BBC TV. This illustrated the use of colour in nature for communication, courtship and defence. The second was the sale of a piece of digital crypto art for a record $69 million (approximately £50 million). This is a collage of every piece of art produced by the artist Beeple since 2007. While this is news on a number of different fronts, the one thing that resonated with me was the myriad of colours in the whole image.

The first episode of Life in Colour was about seeing in colour. It showed how insects see light in the ultraviolet (UV) part of the spectrum, while flowers have ultraviolet markings on them to attract insects to aid in pollination. In NDT we also use ultraviolet light in the augmentation of the dye penetrant process: fluorescent dye is stimulated by an ultraviolet lamp, allowing a higher sensitivity inspection compared to standard red dye. We also use the other end of the optical spectrum, infrared, to detect flaws in the application of thermographic NDT methods. Later in the episode, the ability of fiddler crabs and mantis shrimp to see in polarised light was described. The crabs were able to filter out glare from the sun reflecting off the sea and hence better able to distinguish the presence of potential mates and predators on the beach. Although humans do not see polarised light, it is used in sunglasses to reduce glare and intensity and it is used in NDT technology in photoelasticity and in magnetic flux leakage combined with magneto-optical film.

The visual ability of birds was another topic covered in the programme. Humans have three colour receptors, or cones, in our eyes: red, blue and green. Birds have a fourth cone that is sensitive to violet or UV depending on the species and its environment. One study has suggested that this UV sensitivity detects a greater contrast between the upper and lower surfaces of leaves in dense foliage, making each leaf’s position and orientation stand out very clearly. This compares with our lower capabilities based on green frequencies. This will not surprise anyone who has observed the speed at which birds fly into a tree or a bush. I have yet to see one misjudge it and crash into a branch. A newspaper review of The Bird Way by Jennifer Ackerman drew parallels between the way birds and humans perceive colour and the difference between colour and black and white television.

As someone who once watched snooker tournaments in black and white, I can very much appreciate this comparison. Each bird cone contains a tiny drop of coloured oil that acts like a filter, enhancing the detection of differences between two similar colours.

A further application of the superior visual acuity of birds was reported on the BBC programme Winterwatch, which related how pigeons are able to classify medical images. A resulting quick internet search identified a 2015 study on how pigeons were able to distinguish between malign and dormant images, of mammograms and biopsy slides, with a reliability of near to 90% after 25 days of training. In addition to better colour vision, pigeons have better peripheral vision than humans and have evolved to analyse complex visual patterns and detect anomalies in their search for food.

Although we already use some colour and vision technologies, are we potentially missing out on others that could be developed to further augment NDT, with appropriate research to underpin their design and use? By the way, I am not suggesting that we get together to develop PCN certification for pigeons!

This brings me to the other tenuous connection described above: art. While the particular piece has many other components, my initial reaction to it was in response to the colours it contained. On reflection, a lot of art is about the use of colours to generate a response in the observer, be that in a representation of physical objects or in an abstract way. I have written previously how one cannot be unhappy wearing red trousers and how the sight of my bright blue trainers would raise my spirits. It is well known that nature’s green is relaxing and teams wearing red win more often than those wearing other colours. Everyone perceives colours differently and there are cultural influences. The impact of colours on human reactions and behaviours is another subject that potentially could be used to improve the reliability of NDT.

I was disappointed not to receive any comments written in red, blue or green font on last month’s article. This month maybe?

Please note that the views expressed in this column are the author’s own personal ramblings for the purpose of encouraging discussion within NDT News. They do not represent the views of Jacobs or BINDT.

Letters can be mailed to The Editor, NDT News, Midsummer House, Riverside Way, Bedford Road, Northampton NN1 5NX, UK. Fax: +44 (0)1604 438301; Email: or email Bernard McGrath direct at

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