Tuesday, 24 May 2016

Colour Concepts: 2 - What colour is.... white?

Ok - this might seem like a really strange way to kick off the series proper, but trust me, there's a reason for it. And this article is also technically "Photographing Miniatures 6: White Balance", for reasons which will become rapidly apparent.

To start with, then - how do we see colour? Why is a leaf green?

When light falls on something, three things happen to varying degrees depending on the colour/wavelength of light, namely it can be absorbed, scattered, or reflected. Reflected we'll leave for later (see... ohhh, I dunno? Water? Glass?) but what's scattered and what's absorbed determine its colour.

White light - pure white light - is made up of a spectrum of colours, as per the classic prism demonstration. If you look at your TV, your computer screen, or a LED colour-changing light, closely, you'll see that in fact you can make white (in fact most colours) from a combination of various proportions of red, green and blue (have a play with the link).

So, why are leaves green? Because they've evolved to absorb the red and blue ends of the spectrum for photosynthesis, and scatter the rest, i.e. green wavelengths - result? A green leaf [1]. If something absorbs all wavelengths, it'll be black - and often that means it absorbs the infra-red off the red end of the spectrum as well, and is why black objects get hotter in the sun.

However... the important thing to note is that an object can only scatter what's falling on it. Allow me to demonstrate, with the aid of a camera, my shiny new LED colour-changing living room lights (which use combinations of red, green and blue to make a wide spectrum of possible colours), and a colour balance test card.

The card under 'pure' white.

For the colour-blind (like my wife) the strips are:
top to bottom left:
blue, red, magenta, green, cyan, yellow, grey.
middle small strips:
white, black, cyan, black, magenta, grey, blue
right side:
black, 3 narrow shades of dark grey, black, purple, white, dark blue
Red light

Green light (not very good green, more a sickly greenish-
white, but it's the best the fittings will do)
Blue light

Purple light
Neat, huh? Notice how the white stops being white, because there isn't a full rainbow of colour for it to reflect, and how all the other colours change. Also notice how, for example, you can't pick out the red from the white under red light [2].

Which leads us to the question in the title. Let's have a look again at the test card under fluorescent light, and under warm and cold white from the living room lights.

Very 'Warm' white light (as far down the 'warm' end as my
lights will let me).

About the equivalent of old-school incandescent lights

About the same as natural sunlight.

Natural shade (a very 'cold' blue white).

Under the fluorescents in the kitchen :D
The interesting thing is that what you see in the photos is NOT how your brain processes what your eyes give you - if you looked at any of those in isolation, your brain would correct for the white, as cameras can be set up to do automatically or manually. In this case, obviously, I've deliberately set the camera not to compensate for the different lighting: it's locked to 'daylight in the shade' as that's what I had it set to for the light at Partizan, and you will notice that (for example) the card under the fluorescent strips in our kitchen has a noticeable orange cast, because there's not enough blue wavelengths in the output from the tube).

Of course, how YOU see the above images will also depend on what your monitor thinks 'white' is :D

[1] So why do blue and yellow paint (as opposed to light) make green? 
[2] My wife once wrote a set of crib notes for a set list with our band in red ink. You can imagine her consternation when the stage lights turned out to be predominantly red.

7 comments:

  1. A very interesting article. I knew a war game painter who habitually used cool fluorescent light or bright halogen lamps as nearest to bright daylight. My own view of the matter is that as lighting affects colours in such a marked fashion (apart from other considerations) I don't much worry about how 'right' a colour is.

    As for the colour 'white' itself, I tend to prefer something just a little off white such as the Vallejo 'Ivory'. The old Humbrol gloss 'Mercedes' white was good for a kind of formal 'toy soldier' look to my Airfix AWI figures painted as Imperialists.

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  2. Colour theory tends to be a little complicated. Most folk think in temrs of a colour wheel. An example? In fact there are many multi layered colour spheres! That's where Art college gets you LOL :>)

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  3. I always wondered if we were seeing the same color. At my mother's knee I learned what, for instance, was called the color "Red" - but do I really see the same color I label "red" as the one you learned at your mother's knee?

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    Replies
    1. Well that is a whole different discussion - my wife and I frequently disagree as to whether a colour is Blue or Green - for those shades which lie between. Neither is wrong - but it makes communication very difficult sometimes!

      So we have a ubiquitous colour term - Teal which fills that gap, I still call it blue, she still calls it green, but we both agree it is the same colour!

      I still prefer her to pick the colours for the home,
      but that is mainly because my pallet is mainly grey and beige!

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    2. My wife is likewise blue/green colourblind :D

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  4. Don't get me started! I've had a very long dicussion with an artist on this. I'll throw this into the mix " Why do artists and scientists have different primary colours?" "Why do printers work on secondary colours?" "Why is the sky blue?". Welcome to my world in my previous career as a science teacher. All great questions. There are also substances that take in one part of the spectrum and re-emit it in a different part e.g. optical whiteners in paper and washing powders/ liquids. As you point out Mike the best bit is how the brain adjusts and fills in what "should" be there. Even then and from personal experience you are open to which colour is "right". For example everyone knows US vehicles are usually painted light olive drab, but you show me 10 US vehicles and I guarantee due to manufacturer, batch and fading there will be 10 different light olive drabs. The green/ brown of US infantry is another contencious colour (color) issue. For something so scientifically well understood it is incredibly subjective, but that is what makes life's variety. I could rant on, but ought to stop now.

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