Category Archives: 14 What makes a colour

The Nature of Colour

Hot Air Balloon 2004 - 1/160 at f/6.3, ISO 125

Hot Air Balloon 2004 – 1/160 at f/6.3, ISO 125

As part of the process of understanding colour I am taking a moment between exercises to look a little more deeply how its properties impacts photography. Stephen Shore in his book The Nature of Photographs * (1) says that colour expands a photographer’s palette and adds a new level of descriptive information to the image. He puts forward the view that the viewer is “less stopped” by the surface of a colour photograph than a black and white one because it is how we normally see.

Shore is one of the earliest masters of colour photography so that fact, combined with his profession as a photography professor makes this a good place to start but I want to take a step back and ask what is colour?

Colour is one of the most obvious properties of an object. When we describe something we will often mention its colour and we do this to such a degree that many objects have a colour associated with them that might not be strictly accurate but is accepted as its normal description so we have yellow bananas, green grass, blue sky, green or red apples, red tomatoes and so forth.

However, colour is also a property of light, without light there is no colour and the intensity and thereby the temperature of light will directly effect the colour of an object.

Thirdly, colour is also something that is created by the viewer, our eyes and our brain determine what we see. People with colour blindness are still looking at a red apple but might see it as green and we know that many animals see different ranges of colours than we do.

In summary there are therefore always three factors that influence or create a colour:

  • light,
  • the object and,
  • the viewer.

Light

I am not making any attempt to study light from the perspective of a physicist but to understand colour in photography I need to understand some relevant properties of light.

In simple terms, (probably too simplistic), wavelengths of light from a light source fall on an object, the object modifies the light and it is reflected. If we are there when this is happening we receive the reflected light and “see” the object.

Nature provided us with two useful light sources, the sun which is the most powerful light source a photographer can have at their disposal, and fire which varies in intensity and in its colour. I am discounting starlight and glow worms as non functional in this context.

Fire was harnessed by photographers as early as 1839 when, according to Tuts * (4), L. Ibbetson used oxy-hydrogen light (also known as limelight, discovered by Goldsworthy Gurney) when photographing microscopic objects. Limelight was produced by heating a ball of calcium carbonate in an oxygen flame until it became incandescent. This was the first of many ideas that eventually led to magnesium based flash powder, then flash bulbs and finally to flash guns.

In the 21st century we have a wide range of light sources available to the photographer but each light source interacts differently with a subject and those differences fundamentally effect the reflected light and thereby the colour that the camera sees. This variation is described by the “colour temperature” of the light source which is measured in Kelvin degrees. Bright daylight is 5,400 degrees Kelvin and at this temperature white paper is seen as white, any light source that is rated higher than 5,400 will give a blue cast, anything rated lower will give a yellow, through orange to red cast depending on its temperature. At the extremes a candle is rated as 1,500 degrees K and will give a red cast whereas a fluorescent strip light in an office is around 3,700 degrees K and will give a yellow tint. Flash guns and studio lights are designed to be as near to 5,400 degrees as possible so they mimic sunlight.

The human brain automatically adjusts some of these colour casts so we will still see a white sheet of paper as white under a domestic light bulb whilst photographic film would see a strong orange tint in the same scene. Modern DSLRs have sophisticated colour temperature balancing systems so on automatic white balance they will usually adjust for these colour casts. However, I know from experience that even the best cameras will generally adjust based on the dominant light source and will often ignore secondary light sources that can still tint an image.

Out of doors the impact of colour temperature is more obvious because our brain expects it to be there and makes less adjustment. The warm glow cast by a deep sunset will look orange to us and to our camera. Landscape photographers see early morning and late afternoon light the most desirable partly because of this warming effect.

The Object

The second part of the equation is the object or subject we are photographing. Other than by being whatever colour it is the object has less impact on colour than either the light source or the viewer. A red pepper is a red pepper even with the lights off but how we and the camera see that red is partly determined by the object itself; a pepper is generally a polished surface and therefore reflects light better than a red piece of felt. The surface of the object and its reflective properties and the angle we view it at will all impact the intensity of the colour we see. If we shine an equal amount of light onto a reflective surface and a non reflective surface that are both the same colour and look at each from the same angle the non reflective surface will appear to be the stronger colour. *(5)

Fig. 1 - Red Pepper shwoing how different levels of reflection impact the colour of the object - 1/100 at f/13, ISO 8,000

Fig. 1 – Red Pepper shwoing how different levels of reflection impact the colour of the object – 1/100 at f/13, ISO 8,000

The physics of this effect are complicated but the practical consequence is that a red pepper in direct or bright sunlight or under a flash gun will not appear to be as red as a piece of red felt under the same light. I know from my food photography that it is important to use diffused light and to avoid direct reflections. A direct light source bouncing off a shiny surface straight at the camera is, in effect, a picture of the light source via a reflector and the colour of the object will be lost or reduced in strength.

In fig. 1 I used natural light from a window to light these two peppers. The nearest pepper has about the same amount of light falling on all of its front face but the angle of the light and camera mean that there are burnt out highlights where we cannot see that the pepper is red. Where the light is not reflecting directly into the camera the fruit is more red. The shiny surface of the object combined with the light source have impacted how we see its colour.

The Viewer

Colour has one other property that appears less to do with physics and more with psychology. We are programmed to react to colours in different ways, some of this reaction is probably biological and some cultural so the reaction to particular colours is not necessarily universal.

ND8_7520c2Of the primary colours yellow is viewed as a cheerful colour, the colour of sunlight and summer; it is a bright and dominant colour and is therefore insistent in a photograph.

In nature, along with yellow-green, it one of the colours of spring, gardeners will tell us that white flowers come first each year closely followed by yellow. Add a tint of red and it becomes one of the dominant colours of Autumn.

 

DSC_2077-bird

Red is strong, hot, masculine and powerful and because of its strength it appears closer to the viewer than other colours in a picture and can therefore create a sense of depth in a picture.

It is a colour of warning, many animals use red as a warning colour, and we associate it with traffic lights, road signs and any other sign that seeks to grab our attention.

A walk down any high street in the “sales” season will verify this point.

NK0_2692Angela Wright of Colour Affects a company that specialises in consulting with people and companies who are choosing colours. * (3) argues that our reaction to red is physical whereas our reaction to blue is intellectual.

Blue is cool and calm, the colour of the sky and the sea and unlike red it tends to recede into a picture.

Soft blues are recognised as being particularly serene and calming but can be cool to the point of unemotional or unfriendly according to Wright * (3).

NK0_0757-green-leaves-with-snailMichael Freeman explains that, to the painter, green is a secondary colour but in the world of colour film , computer monitors and digital cameras it is a primary, and hence we have RGB. * (2)

Green has more of the psychological attributes of its neighbour blue than its other neighbour yellow and is generally another calm colour, but it is also the colour of nature and spring and can appear fresh and vigorous. Wright argues that, because it is in the centre of the spectrum it is the colour of balance and she believes that we associate green with well-being on a very primitive level, green vegetation means that there is no danger of going without food.

The Earth is known as the blue planet because of the scale of her oceans but for most humans the predominant colour around us is green and it is the first colour that city planner bring into urban areas to comfort the inhabitants. One of the remarkable attributes of green is it’s variety of hues, a walk through woodland will reveal a seemingly endless array of greens.

These are obviously generalisations but when composing a picture we should be conscious that the colours we include will affect the viewers reaction and potentially create the “mood” of a photograph. Colour associations mean that we can emphasise a point or change the meaning of a picture by building certain colours into the scene.

Sources

Books

* (1) Shore, Stephen. (2007) The Nature of Photographs: A Primer. Second Edition. London: Phaidon Press.

* (2) Freeman, Michael, (2007) The Photographer’s Eye. Lewes: The Ilex Press.

Internet

* (3) Wright, Angela, (2008) Colour Affects. www.colour-affects.co.uk/psychological-properties-of-colours

* (4) TUTS : Tutorials, inspiration and videos to help you learn. photography.tutsplus.com/articles/a-brief-history-of-photographic-flash–photo-4249

* (5) Konica Minolta Sensing. www2.konicaminolta.eu/eu/Measuring/pcc/en/part3/02.html

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Exercise 22 – Controlling the Strength of Colour

Fig 1. Control Shot - 1/100 at f/13

Fig 1. Control Shot – 1/100 at f/13

In this exercise we are asked to take a control picture using an average exposure and the take a series of photos starting with 1 stop over-exposed down to 1 stop under-exposed in 1/2 stop steps. To increase the arneg I chose to start at 2 stops under-exposed through to 2 stops over-exposed.

Fig. 2 Histogram for Control Shot

Fig. 2 Histogram for Control Shot

Fig 1. is a control shot at the settings calculated by the camera. Most of the time I use aperture priority and left it on that setting for this exercise. I chose f/13 to ensure that everything was in focus and the answer would not be confused by any blur.

I took a screen shot of the histogram in Photoshop for each image to allow me to see how that changes. In the control shot the histogram is weighted towards the left which is not surprise as the picture is mostly fairly dark tones.

Fig. 3 Over Exposed Test Shots

Fig. 3 Over Exposed Test Shots

Fig. 3 shows the series of over-exposed shots ranging from plus 1/2 a stop on the right to plus 2 stops on the left. It is very clear that the colour saturation decreases with each 1/2 stop of over-exposure. Somewhere between plus 1/2 and plus 1 stop would give the most balanced histogram.

Fig. 4 Under Exposed

Fig. 4 Under Exposed Test Shots

Fig. 4 continues the sequence from less 1/2 stop on the left to less 2 stops on the right. The conclusion is clearly that colour becomes less saturated the more an image is exposed and visa versa.

It is important to be able to predict and, to some degree, control colour saturation for a number of reasons. It is part of the decision process when taking and often when post processing a picture. For landscapes I would generally lean towards under-exposure to ensure that I have captured all the detail in the highlights but also because I often want saturated colours. For example, in the bright conditions of Turks and Caicos I under-exposed by 1/3 of a stop during the brightest parts of the day. For food photography I am trying to present food in as natural a manner as possible so I will adjust my exposure and lighting to to give me a neutral result i.e. neither de-saturated or over-saturated. For portraits I am now often consciously over-exposing as I find many younger people like a slightly de-saturated look. I notice that many modern wedding photographers over-expose all their shots so I presume that this is what their clients require.