Christoph Wagner Colour Theory

Transcription

1 Colour Theory

2 Hue, Saturation and Lightness (HSL) This model is one of the most intuitive ones in describing colour and I find it most useful for our purposes. There are other models, but we'll focus on this one. It is sometimes known as HSB (hue, saturation, brightness) or HSV (hue, saturation, value). Hue is the most fundamental part of colour. It refers to a specific wavelength on the energy spectrum. Most colours are a mixture of different hues. When we normally refer to a colour in common language, what we refer to is usually the dominant wavelength. Saturation is an expression of how much hue is in a colour. It defines the intensity and purity of a colour. The more of the spectrum is mixed into a colour, the less intense, saturated, it will appear. Saturation is a measure of the degree to which a pure colour is diluted by white light. L106 & L107 1 Looking at the sample of L106 and L107 in comparison, you ll see how the more saturated, purer Primary Red contains much less of the rest of the spectrum. Brightness is just that, the brightness (or lightness) of the colour. 1

3 Colour pickers on the newer lighting desks make use of this system by presenting something like this HSV-Hexagon: HSV Hexagon 2 Colour mixing There are two principles of colour mixing used in lighting, additive and subtractive

4 In additive mixing we layer colours on top of each other to create different colours, fo example by using several different lanterns with different colours all focused onto the same space, or in LED technology where (at least) three different coloured LEDs are mixed together to create a colour (RGB mixing). The primary colours of additive mixing are Red, Green and Blue. These can be mixed to create the secondary colours Cyan, Magenta and Yellow. In subtractive mixing we use filters to take away parts of the spectrum to create new colours. So, for example to create a pink light we put a filter in front of a white light. This subtracts (filters) all colours other than the pink. The primary and secondary colours are the reverse of the ones from additive mixing, so our primary colours are Cyan, Magenta and Yellow, and secondary Red, Green and Blue. Secondary mixing is used in most moving lights (CMY mixing), where the three colours are mixed in various degrees of saturation to create endless combinations of colour. Looking at the colour mixing charts the colour opposite each other are called complementary colours. Using complementary colours from opposing angles on the stage can create pleasing effects. It enhances contrast while mixing together towards white, creating a brigth centre. There is a simple technique to help you find the complementary colour to any filter you might use. All you need to do is stare at the swatch of the filter for about 30 seconds, then look at a white piece of paper. The afterimage your retinas produce is the complementary colour to the one you've been staring at. Colour Temperature Different sources of light have different colour temperatures. Colour temperature is an expression of the colour of a source of light and is measured in Kelvin. 3

5 At the lower end of the temperature range the colour of light looks more amber, at the higher end it will look more blue. In practice this means that the light source used in a lantern has a big influence on the perceived colour of the light and also on what effect colour filters will have. A good example of this is the new Lee LED filter range. In order to create commonly used colours with cool white LEDs rather than tungsten light sources you need to use filters that appear to be completely different colours. An interesting extreme in the world of lamps is the low-pressure sodium vapour lamp. You can still find it used in street lights here in Glasgow, although it is slowly being replaced by other types of lamps. It has a very low colour temperature, creating that orange street light look that we all recognise. What makes the low-pressure sodium so particularly interesting is its extremely narrow colour spectrum. Because if this incredibly narrow field of colour it has a very low colour rendering index (CRI). This is a measure of how well you are able to distinguish colours under a certain light, and it is influenced

6 by how wide an area of the spectrum is contained in the light source. Tungsten halogen lamps have a CRI of 100, as they are considered to be faithfully showing colour, whereas low pressure sodium has a CRI of 5. This can be used to great effect on stage, it is possible to turn the stage monochrome if you only use low-pressure sodium lights. Not quite black & white theatre, more black & orange, but because the eye adjusts to the orangeness you do get a sort of black & white film feel. Another side effect is an apparent clarity of image, because the human eye is particularly sensitive to the orange part fo the spectrum. What colours? Most generic theatre lanterns use tungsten lamps, so that is what we will be talking about mostly when we're talking about the use of colour filters. There are cold, warm and neutral colours. Into which category a colour falls is relative, it depends on what other colours are being used on stage either at the same time or just before. Generally speaking, blues are cold, ambers warm. Lavenders and greens are neutral and their relative warmth depends heavily on the context they are used in. As mentioned briefly earlier the human eye is more sensitive to the warmer part of the colour spectrum. This has an influence on our perception of distance. Using warmer colours will make things and people appear nearer than colder colours. Colour correction filters are designed to change a lamps colour temperature to that of another light source, For example L201 is designed to correct the colour of a tungsten lamp to that of daylight. It's opposite colour correction is L204, designed to turn daylight to tungsten. This is also what the term mired shift describes. Mired in this case comes from micro reciprocal degree and is a unit to measure colour temperature. It can help when you are trying to choose colours for a show to think about what white is in your show. As we've seen on the colour temperature chart there is a wide range of colour that can appear to be white in different contexts.