1. International Conference on Light and Color in Nature
31st May – 3rd June 2016
Granada, Spain

2. Colour flowers Thomas Bangert thomas.bangert@qmul.ac.uk of

3. Sunlight Sunlight is mostly spectrally flat over the visible spectrum
direct sunlight in the range of nm varies no more than 5% from the average
There is very little UV light
there is a notch at 430nm and a sharp decline below 415nm
There is plenty of light beyond red (IR), but not flat above 700nm

4. Origin of the Flower? 200 million years old
stems from the age of the dinosaurs
dinosaurs (ancestors of birds) were the first animals with really good colour vision
Flowering plants use birds and other animals (like insects) to reproduce.
it is very important to attract the right kind of animal

5. Purpose of the Flower? to attract the right kind of animal
which means advertising!
often a reward is offered
many animals (including humans) like sugar
many animals need sugar to live
sugar is expensive to produce
rewards are kept to a minimum – preferably no reward at all
which makes it important for the animal to visually discriminate – to see good from bad

6. Colour of Flowers Flowers do not have colour
flowers only reflect or absorb light from the sun
plants usually absorb all light they can use for photosynthesis – except a little bit of green
Colour is purely the product of the animal’s visual system
Colour does not exist as a physical property

7. Why investigate the Colour of Flowers?
measuring the ‘colour’ of flowers is very easy
understanding the visual system of animals is very difficult
animals and flowers have co-evolved for hundreds of millions of years
the way flowers absorb and reflect light comes from the way animals see
animals dedicate a large part of their brain to vision – the visual system
the way flowers reflect & absorb light can help us understand the visual system

8. Colour Vision dividing the spectrum
Human
Bird
4 sensors
Equidistant on spectrum
How are these sensors used?
What information do they code?
What does colour mean?

9. What we know about colour vision
we can make sense of monochromatic light
monochromatic light is not common in our natural environment
flowers are never monochromatic
the closer light is to monochromatic the more pure the colour appears

10. what we know from television
b&w images need 1 number per pixel
colour should be backwards compatible with b&w
we can code colour with 2 extra numbers (channels)

11. opponent process we cannot see both red and green OR blue and yellow
because colour is coded by 2 channels – 2 opponent channels
for a total of 3 channels including b&w
a positive number codes for one colour and a negative number codes for another
you get negative numbers by subtracting

12. Rough Guide to Colour R-G Y-B we divide the spectrum up into primaries
one for each sensor
gives us 4 numbers
we pair up the primaries
we subtract the pairs
gives us two numbers
we assume colour is monochromatic light
allows us to calculate where we are on the spectrum from 2 colour values
R-G
Y-B

13. … expressed another way
x and y coordinates map to any colour

14. Measurement
Instrument: X-Rite i1Pro spectrometer Range: nm Resolution: 3.3nm Precision: 3 decimal places designed for monitor calibration and print industry … works equally well measuring flowers, but has limited resolution
white wild european daisy (bellis perennis)
Spectrum from to nm in 107 steps
4.336, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

15. White
Human Solution:
reflect as much light as possible
don’t worry about accuracy
reflect over 90% of light
deviation is up to 10%
White is the absence of colour to an animal with colour vision How to present the best white? a human solution is very different from nature:

16. The Rose Rosa Spinosissima range: 460-740nm max deviation: 0.95%
reflectance: 57%
average deviation: 0.18%
max deviation: 0.95%
The Rose

17. The Rose Rosa Carolina range: 500-740nm max deviation: 0.4%
reflectance: 50%
average deviation: 0.1%
max deviation: 0.4%
The Rose

18. The Rose Rosa (garden hybrid) range: 440-700nm max deviation: 7%
reflectance: 53%
average deviation: 1.2%
max deviation: 7%
The Rose

19. Pelargonium Zonale (cultivated hybrid) range: 440-740nm
reflectance: 60%
average deviation: 0.07%
max deviation: 0.74%
Pelargonium

20. Primula vularis (cultivated hybrid) range: 460-740nm
reflectance: 52%
average deviation: 0.15%
max deviation: 1.5%
Primula
[black center]
range: nm
reflectance: 0.35%
average deviation: 0.03%
max deviation: 0.14%

21. misc

22. Nature’s Solution to White can tell us a lot
white flowers do not reflect as much light as possible but rather reflect light precisely
white flowers reflect visible light exactly equally
area of equality equals the visible spectrum of the animal
flowers can precisely control absorption/reflectance
spectrum of flowers is by design not accident
very few flowers reflect light below 450nm
most flowers reflect far beyond human upper limit of red – into IR
consensus view that animals like birds see UV but not IR is probably wrong

23. area of visible spectrum is almost completely flat (equal energy spectrum)

24. visible spectrum of target animal
far into IR
No UV

25. Human Solution:
divide spectrum into 3 regions – RGB
colours are levels of each region
adding light: RGB absorbing light: CMY
Colour
What is colour? nature has a very different answer than the human solution

26. HDR Television

27. Computer Monitors

28. Human Solution
three primaries: Blue Green Red

29. Nature’s Solution to Colour
very different to colour reproduction schemes invented by humans
common underlying theme
no indication of any primaries

30. Rose Rosa (garden hybrid) range: 440-700nm
angle: varies low reflectance: 0.33%
Rose

31. Pelargonium Zonale (cultivated hybrid) range: 440-700nm
angle: high low reflectance: 0.32%
Pelargonium

32. Sunflower you can have any colour you want as long as its yellow
Helianthus
range: xxx
angle: steep low reflectance: 1.1%
Sunflower you can have any colour you want as long as its yellow

33. Poinsettia colour is not great by default
Euphorbia Pulcherrima
range: xxx
angle: low low reflectance: 1.85%
Poinsettia colour is not great by default

34. How Nature Defines Colour
one area of absorption – equal and extremely high absorption
one area of reflection – same as white
colours change by a spectral shift of absorption/reflection boundary
range is yellow to red
no such thing as green or blue flower
shift is circular, with red to purple
range can be coded by one number (dimension)

35. colour by spectral shift
reflects like white
range is yellow to red
absorbs like black

36. purple indicates circularity

37. Conclusions precision is due to difference measurement by sensors
white when colour sensors exactly negate each other
colour is the contrast between precise absorption and precise reflection
indicates 2 sensors for each area
current colour reproduction technology is woeful in comparison to flowers

38. comparing white: the orchid with an apple 5K display

39. Questions?
References
Poynton, C. A. (1995). “Poynton’s Color FAQ”, electronic preprint.
Goldsmith, Timothy H. (July 2006). “What birds see”. Scientific American: 69–75.
Chittka, Lars. FReD floral reflectance database
Bangert, Thomas (2008). “TriangleVision: A Toy Visual System”, ICANN Hurvich, L. M., & Jameson, D. (1957). An opponent-process theory of color vision. Psychological Review, 64(6), Wyszecki, G., & Stiles, W. (1967). Color Science. John Wiley. MacAdam, D. (1985). Color Measurement. Springer. The Colors of Flowers. (1882). Scientific American, 13,