search.noResults

search.searching

dataCollection.invalidEmail
note.createNoteMessage

search.noResults

search.searching

orderForm.title

orderForm.productCode
orderForm.description
orderForm.quantity
orderForm.itemPrice
orderForm.price
orderForm.totalPrice
orderForm.deliveryDetails.billingAddress
orderForm.deliveryDetails.deliveryAddress
orderForm.noItems
INSTRUMENTATION | COLOUR PERCEPTION


A quick look at colour


Colour is complex. Here colour measurement specialist Datacolor provides some basics on how the human eye perceives colour and how that process can be instrumented


Main image: The human eye is an impressive colour perception device but has its limits as a colour matching tool


Human perception of colour is not straightforward and science is still uncertain of the precise processes involved. According to traditional trichromatic theory (also called Young-Helmholtz theory), rod-shaped photoreceptor cells in the retina of the eye allow us to see at very low light levels but only in shades of grey. Different cone- shaped cells allow us to perceive colour in brighter light through their response to roughly three different wavelength spectra: blue (absorption peak around 445nm); green (535nm); and red (565nm). However, a newer alternative theory postulates that colour vision depends upon three receptor complexes with opposing actions: light/ dark (white/black), red/green, and blue/yellow. In any case, what is clear is that the way in which we perceive colour is complex. Humans are pretty good at recognising the


48 COMPOUNDING WORLD | July 2019


colour of familiar objects, even under different ambient lighting conditions. This adaptation of eye and brain is known as colour constancy. It doesn’t apply to subtle colour variations, though, and does not counteract the changes in colour due to intensity or quality of light. We may also be able to agree with each other on the wavelengths that define basic colours, although this could have more to do with our brains than our eyes. In a 2005 study at the University of Rochester in the US, for instance, individuals were shown to perceive colours the same way even though the number of cone receptors in their retinas varied widely (researchers found that when volunteers were asked to tune a disc to “pure yellow” light everyone selected nearly the same wavelength, for example). However, the situation gets more complicated


www.compoundingworld.com


PHOTO: SHUTTERSTOCK


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68