2.6 Colour Matching

Fixtures of different types use different methods to perform colour mixing. Sending the same parameter values to fixtures of different types might produce a different colour on each type. For example, sending C=50%, M=50%, Y=0% will always produce a shade of blue, but it'll be a different blue with different fixture types.

Usually, you have to compensate for this yourself by manually creating colour palettes by eye to produce similar colours on all fixture types. This is a time consuming process, and later restricts you to using the palettes you have already set up.

The Hog 4OS's colour matching system provides a new way to choose colours, without these problems.

2.6.1 Colour Models

Traditionally, colour mixing fixtures use the CMY (Cyan, Magenta, Yellow) system to uniquely define each colour they can produce. With the increasing popularity of LED fixtures, the RGB (Red, Green, Blue) system is also becoming more common. These two systems are called ‘colour models’. Any colour can be represented equally well by either of these two colour models - they are just different ways of conveying the same information. Many other colour models exist, perhaps the most useful of which (for lighting control, anyway) is the HSI (Hue, Saturation, Intensity) system:

  • Hue: This is the term used to specify the colours position in the possible range a colours, from red, going through yellow, green, cyan, blue and magenta, and finally returning to red. As the range ‘wraps around’, you can visualise it as a circle with the colours positioned around the edge, with red at the top, green at the lower right, blue at the lower left, and the intermediate colours in between. The angle between 0 and 360 degrees specifies the hue of the colour: red has a hue of 0 degrees, yellow has a hue of 60 degrees, and cyan has a hue of 180 degrees; see Figure 2.6, “The HSI Colour Wheel”.

  • Saturation: This is how ‘strong’ or ‘pale’ the colour is. Pale colours have low saturations, while strong colours have high saturations. Saturation is specified as a percentage between 0% (white) and 100% (the strongest possible saturation).

  • Intensity: This is simply a measure of how much light is being emitted, from 0% (black) to 100% (the brightest possible). This is identical to the dimmer control on most fixtures.

Figure 2.6. The HSI Colour Wheel

Diagram showing the HSI colour wheel

With these three pieces of information (hue, saturation and intensity), every possible colour can be represented. As most fixtures already feature a dimmer to control the intensity, it is only necessary to specify the Hue and Saturation to uniquely represent any colour.

The Hue and Saturation of White Light

White is defined as the colour with 0% saturation; the hue doesn't matter. However, while tungsten and arc lamps both produce ‘white’ light, when you compare them side to side their colours are considerably different. The tungsten lamp has a ‘warmer’ colour with a higher red and yellow content, while arc lamps usually have a ‘cooler’ light with more blue in it. One version of white is not more ‘correct’ than the other, so either may be chosen to be the reference point depending on the situation. In a theatrical environment where tungsten sources are more common tungsten white is likely to be most appropriate base. In other environments predominantly using arc sources, it will be more convenient to use arc white; for information on changing the white point, see Using Colour Matching.

2.6.2 The Colour Matching System

The Hog 4OS's colour matching system is based on a fixture library that contains colour calibration data for the fixture types in use. This calibration ensures that fixtures of different types can easily be assigned to the same colour, including to a chosen definition of ‘white’. It can also be used for fixtures that have not been calibrated, but the colours that will be produced may not match the colours from fixtures that do have calibration data.

You can choose colours using the parameter wheels to assign cyan, magenta and yellow values or hue and saturation values, or you can use the on-screen visual colour picker; see The Colour Picker.

It is preferable to program using Hue and Saturation whenever possible. The advantages are:

  • Selecting colours using Hue and Saturation or the colour picker will produce the same visual colour output on all calibrated fixture types.

  • You can use fanning and effects on Hue and Saturation to produce attractive looks quickly.

  • When you use Hue and Saturation to pick a colour, Hog 4OS will automatically use the best possible DMX value settings for each fixture type to achieve maximum light output from each fixture.

  • You can crossfade from a saturated red to a saturated green without the saturation changing. The crossfade will work through all the saturated colours between red and green, rather than taking an unexpected path to get there, as can happen when using CMY programming.

  • Crossfades between colours recorded using Hue and Saturation will remain matched on all fixtures through the progress of the crossfade. This produces a better, more even-looking colour crossfade.

[Tip]Tip

It is strongly recommended that you do not change between the HSI and CMY systems within a show.