Colour Science

Most human colour perceptions can be generated by a mixture of three colours called ‘primaries’. These three colours (red, green, and blue) are used to reproduce colour in film, television, print, photography, etc. These ‘primaries’ are the best method to replicate colours from the spectrum, however it can never been completely accurate, the reproduced colours cannot match saturation, hue, and spectra precisely. This is where a variety of colour spaces come into play, each one offering a different range of colours, the larger the colour space the better the range of colours. The range of colours that can be reproduced within a given colour space is called the ‘gamut’. The mass used colour space is known as ‘Rec 709′, implemented on domestic televisions and monitors, however this is one of the smallest electronic colour spaces in comparisons to the entire visible light spectrum. The following chart shows how much of the colour spectrum Rec-709 actually covers (it is listed as ITU-709).

f55-camera-tab6-1Because of the increased development in camera and post-production facilities a future-proof high dynamic range, wide colour gamut has been developed known as ACES (The Academy Colour Encoding System). This colour space is larger than the visible light spectrum, making it completely future proof. The following diagram compares ACES to Rec 709 (domestic), SMPTE (cinema) and the visible light spectrum.

ACES

This is currently a theoretical colour space, it is possible to edit RAW footage within ACES but it is extremely difficult as you cannot see differences made outside the range of the monitor. A Rec 709 monitor will only show the colours within that space, even if the footage is shot within a larger colour space. When it comes to shooting at a greater dynamic range (e.g. cinema) the monitor used for colour grading will also match this space in order to grade effectively. Currently the best coverage provided by a monitor is around 82% of the visible light spectrum, the figure below shows Sony’s future plan for Laser Projectors in order to cover more of the light spectrum.

Colour Space

The intended 97% could change the way we view films completely. The immediate thought of this only suggests a positive outcome, we would be able to electronically replicate and transmit the world around out. However you could argue that getting closer to a truer representation will make everything seem hyper-real, and something an audience would not enjoy. A good example of this is The Hobbit, the film was shot at 48fps rather than the traditional 24/25fps. This provided a clearer image, however a lot of people did not enjoy the effect it had on the image, making it look too real as if you were watching a television soap opera. We have become so used to traditional film over the past century and we continue to replicate it electronically is trying to advance the colour space and camera sensors/projectors necessarily a good thing? For now I will leave this as a rhetorical open-ended question, but it is definitely worth considering as we continue to push technology to make realistic gamut.

RGB_Cube_Show_lowgamma_cutout_a

One final point when discussing colour space is the argument that the RGB module is better to be viewed as a cube as opposed to flat on a grid (as used in all previous diagrams featured). When all components are at their maximum amount white light is produced, if these values are decreased grey tones are produced. By viewing the colour in a three dimensional space you can easily see how changing the amounts of each channel effects the resultant hue, this way you can also plot exact tones by coordinates in a three dimensional space. The RGB cube has eight vertices, one the location of black, one white, and the other six form a curve to connect black and white (red, yellow, green, cyan, blue, and magenta). Delving deeper into this representation of colour space becomes extremely in depth to the point of forming another investigation. Further reading on colour space models can be viewed here – RGB Cube & HSV Cone.

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