Additive Mixing Process
Additive mixing processes can be thought of as perceptual or internal mixing processes (compared to the subtractive mixing process, which can be thought of as a physical or external a mixing process). There are several variations of the additive mixing process.
1. Simple Additive Mixing Process
Two separate beams of white light passing through blue and yellow-coloured filters produce an additively mixed white, where the coloured light beams overlap. Image courtesy of Maggie Maggio.
Simple Additive Mixing occurs when lights of different colours from two or more sources combine or add together before the combined light beam reaches your eye. The lights from different sources add together, and your visual system interprets all the light entering your eye as one colour perception.
The Figure demonstrates what happens when a beam of white light is sent through a blue coloured filter, a second beam of white light is sent through a yellow- coloured filter, and the two coloured light beams overlap. In this case the overlapped areas result in a mixed colour close to white.
2. Optical Mixing Process
In Optical Mixing, similar to Simple Additive Mixing, lights of different colours from two or more sources combine or add together before the combined light beam reaches your eye. The lights from different sources add together, and your visual system interprets all the light entering your eye as one colour.
2.1 Example: Spatial optical mixing on screens
One example of optical mixing occurs as we view colours on our phone, computer or television screen. These types of displays contain pixels, each containing multiple sources which emit light over narrow wavelength ranges, typically centred on short, middle and long wavelengths, corresponding to blue, green and red coloured light beams. To generate different colours on a screen, each source within each pixel emits varying amounts of light, which is then interpreted by our visual system.
Representation for magnified blue, yellow and white areas of a screen. Magnified areas depict which sources emit light within each pixel, for each additive spatial optical mixture. Image source: David Briggs’ Figure 4.4.2 D from Additive-averaging and pointillist mixing.
2.2 Example: Averaging/Partitive Mixing
Some optical mixing is also known as averaging/partitive mixing. It is a form of additive mixing where there is a dilution or averaging of the intensity of light that enters our eyes compared to simple additive mixing. The mixed colours appear more muted or diluted compared to the potential vibrant mixtures found in simple additive mixing or spatial optical mixing on a screen. The averaging can occur either spatially, or temporally.
The figure below shows examples of spatial optical mixing. In A-C, stripes of alternating colours become thinner and thinner, until they become too thin to be distinguished as separate sources. Their combined light enters the eye to generate the sensation of a single colour. In this case, the achromatic colour of grey is perceived.
Examples of spatial optical mixing. Image source: David Briggs’ Figure 4.4.2 A-C from Additive-averaging and pointillist mixing.
2.3 Example: Temporal additive mixing with spinning disks
In temporal additive mixing, light from sources become averaged in time when they are moving too rapidly to be distinguished. This effect is seen when mixing coloured areas using a rapidly spinning disk.
Preparation of a disk to demonstrate comparative mixing of blue and yellow-coloured paints. Central portion of disk contains subtractively mixed blue and yellow paints. Outer portion of disk contains separate areas of blue and yellow, which will optically mix when disk is spun rapidly. Image courtesy of Maggie Maggio.
Demonstration of temporal optical mixing with a spinning disk. GIF courtesy of David Briggs.
See a thorough discussion of comparative mixing processes; and see also: Mixing processes.
