Psychophysics of Colour
To reproduce a single colour frame of moving image, a DLP projector overlays three discrete images in quick succession, their output synchronised with the motion of a filter wheel divided equally into segments of red, green and blue, the three primaries that correspond with the colour sensitivities of our retinal cones. From a technical perspective the full colour image that we perceive never exists, but is only created in the audience’s perception by additive colour synthesis. From the perspective of the machine there is only of a sequence of distinct red, green and blue images, whose intensity is micro-managed at the level of the individual pixel. Colour, as experienced in both DLP projection and unmediated human perception then, is never ‘true’ (as BenQ claim), but always a technical construction.
Through processes such as this, the production and reproduction of the digital image is founded on an externalisation of our perceptual faculties. Digital image technologies are designed so explicitly to be seen, that their technical specifications not only reflect but directly imitate the anatomical construction and perceptual effects of human vision. The pixelation of a digital micromirror device (DMD) reproduces on an optoelectronic grid the mosaic of cones lining the retina, while the colour wheel enforces a trichromatic filtering that targets their colour sensitivities. We can therefore conceptualise the optical mechanisms of a DLP projector as an attempt to build a projecting eye, a luminous electronic retina radiating colour onto the surfaces of its environment.
The optical principles on which this mechanism is based originate in the trichromatic theory of vision, hypothesised by Thomas Young in 1802 and subsequently proven through the psychophysical experiments of Hermann von Helmholtz and James Clerk Maxwell. The colour triangle, initially posited by Young (below, left) to describe colour spatially as created between the three poles of red, green and – as he supposed – violet has now become a standard means of measuring the colour gamut of various display technologies, in which different technical standards can be described as differing sizes of triangle within the complete perceptual colour space circumscribed the CIE system (below, right).
This chromatic space postulated by Young was subsequently mapped empirically by Maxwell. To conduct his experiments, Maxwell constructed a handheld wheel (below, left) onto which could be clipped overlapping discs of different colours. The wheel was then spun fast enough that the colours mixed together in the perception of their observer in much the same way that the discrete frames of a moving image appear as continuous motion. Using this simple instrument, Maxwell was able to quantify the perceptual effects of different ratios and combinations of the three primaries. In so doing, Maxwell ascribed numerical values to the proportions of vermillion, emerald and ultramarine used to achieve different tones, shades and hues; producing a series of discrete values within a field of subjective experience that had previously been understood as a continual spectrum. To quantify colour in this manner can be understood as a kind of proto-digitisation, and Maxwell’s method prefigures the numericalisation of colour gamuts in media technical standards from the 216 ‘websafe’ colours to the considerably wider gamut of 16 million colours that can be coded in a six digit RGB hex code.
Maxwell’s conclusion from these perceptual experiments: “that the judgment thus formed is determined not by the real identity of the colours, but by a cause residing in the eye of the observer” (link) established human vision as a manipulable system of perceptual limitations. This psychophysical conception of sight as fallible and slow relative to mechanical motion persists throughout our contemporary media environment, and is the foundation on which all moving image technologies rely. And – in the colour filter of DLP projectors (below, right) – Maxwell’s colour wheel persists today as a techno-chromatic mechanism of externalised sight. A spinning disc originally used to measure the chromatic operation of the human vision has now become a central component in the reproduction of projected colour. The dissolving of biological sight into its trichromatic primaries was diagnosed by the exact same mechanism that now resolves those colours before us.
In 1855, when black and white photography was still in its experimental infancy, Maxwell proposed a system for producing a colour photograph. By photographing the same scene through three separate red, green and blue filters and then, using magic lanterns, projecting each result through its respective filter on top of one another, he hypothesised that a full colour image could be produced. This process was successfully demonstrated six years later creating a now much reproduced image of a tartan ribbon. In DLP projection each frame of the moving image replicates exactly Maxwell’s process of additive colour synthesis, combining three discrete monochromatic images in the audience’s perception. Maxwell’s trichromatic system of projection is now automated by contemporary cinema to occur, in some systems, as often as ten times for every frame, or 250 times a second.
Such accelerations of photographic temporality began, as Paul Virilio writes, from the moment of its invention: “from Nièpce’s thirty minutes in 1829 to roughly twenty seconds with Nadar in 1860” (p. 21), and rapidly continued past the frame rate of film projection to now operate habitually at rates far beneath human temporal perception. If celluloid cinema enabled the capture of movement by the intervention of a rotating shutter, fragmenting time into a sequence of freeze frames, then in DLP it is this now historic whole of the individual frame itself whose unity is dissolved both spatially into pixels and chromatically (and, as we will see in next post) temporally into three subsequent perceptual primaries.
