Colour in VFX
How colour is measured and replicated in digital outputs...
When capturing colour in film or photography, there are different settings that are used by camera operators. The human eye is able to pick up many different shades and hues of colour from the spectrum which have now been assigned a numerical value, this means a computer can also understand and categorize the colours in a similar way to our minds. These colours all come from pure RED, GREEN and BLUE (RGB) values, a computer or other electronic visual output would have difficulty in replicating the pure colours but will match them as closely as they can. Due to the quality of the output, the colour depth/clarity in a film projected on to a screen in a cinema will look a little different to one shown on a monitor ort television/phone screen.
Understanding Colour Theory and Space
Colour Space is used to accurately measure different colours and allows a computer to manipulate or correct colours for display on different outputs.
This is a screenshot from the properties menu of a 'Write node' in Nuke, the colour space options include sRGB, this is the standard RGB format created in the 1990's by electronics companies (Microsoft,HP) to standardize colour output across electronic devices. Older Cathode Ray Tube monitors required JPEG files to be brightened like this in order to display correctly on-screen.
Depending on the quality of the device, those with a high colour gamut are able to output a wider scale of colours. Some newer gaming monitors and high end consoles (LCD/OLED) offer HDR colour resolution which has an even higher performance colour output.
Coordinates for sRGB colours are based on the (International Telecommunication Union Radiocommunication Sector’s standard which is also known as Rec .709 and ITU 709 and was created for HDTVs. The linear output option in Nuke will read the colour space of the input image and use this for the output.
Below is an example of different outputs on the same HDR image in Nuke:
OUTPUT: BT1886
OUTPUT: REC709
OUTPUT: Linear
Above is an example of a HDR image in Nuke, the colour space graph is displayed in the properties. As the mouse is ran across the image, the colour data this shown in RBG against the master colour line.
Based on the format an image is stored in, the colour space will allow the artist to interpret the colour language/profile and make correct changes. A Jpeg image will generally be stored in sRGB whereas an open EXR format can usually be Linear.
(The VFX Color Pipeline, 2021)
This diagram shows the ideal pipeline for colour management in VFX, footage is linearized to make any editing/manipulation easier. A 'look' or series of 'looks' are applied to the shot and recorded in the form of LUTS (Look Up Tables); the LUT doesn't interfere with the colour space of the footage, instead it serves as an applied effect over the top. Lastly the VFX artist converts the footage from the common linear colour space to the correct display output (sRGB/HDR), this data is baked into the final write and can be accessed/read by the digital output correctly in future. The end result of this kind of colour correction is footage that is as accurate as possible in terms of colour output.
Gamma correction during editing ensures that the luminance of a piece footage is consistent, the merge of black and white elements should be smooth so that when clips are layered on mattes or other footage it doesn't look too blurry or messy.
Generally the film/television show will have a specific colour theme which dictates the atmosphere and visual style, much like sound design, the colours of a film can comfort or disturb viewers depending on the desired effect. Colour drives the visual storytelling on-screen and can create an emotional response, subtle highlights of colour draw the eye. The VFX editor will get an understanding of which colour space a director/producer wants to work with and help to keep this consistent through the composition, concept art and storyboards/previz will likely feature the colours as a guide for others to work from.
There are ways of shooting footage that compositors now use to extract as much colour data as possible, shooting in LOG mode allows much more data to be captured and stored for use in post-production/editing stages. The hue, saturation and brightness of a shot can all be altered to convey a particular atmosphere, some films have more prominent colour spaces than others (for instance a film set in a cold environment may use more cool blues tones throughout). The saturation of a piece of film can affect the perceived depth, colours that are complimentary are often used to separate foreground and background. Some film makers also use more muted colour palettes on purpose to convey a particular tone. The temperate of a shot is measured in 'Kelvin units', the higher the number, the cooler/bluer the temperature. In black and white films, silhouettes are used to show complete contrast between elements; there are tones between solid white and black which can be detected and used to create more depth in a shot.
A good example of the use of colours is in the 2019 Joker movie. The polarizing light and dark attitude of the main character is visually presented throughout the film, Joker himself often wears bright colours but is overcome with darkness and despair which consumes him. His journey into madness is documented through colour, a lot of the most atmospheric scenes are filmed during 'golden hour' when natural cyan tones in the evening light mix with yellows/fluorescent man-made elements. Lawrence Sher (Cinematographer for Joker-2019) speaks about how Sodium Vapour used in older streetlamps bathes sidewalks in a particular evening glow, it not only specifies the time period in which the film is set (70's/80's Gotham City) but creates contrast between natural evening lighting and night-time city light pollution. It also draws the audience's eye across a scene to highlight important elements or warmer looking places for the character to gravitate towards. As the Joker wanders towards his apartment building, more yellow tones appear in shot, almost guiding him home. When he finally reaches his apartment and enters, a warmer yellow tone is added to covey a more homely atmosphere compared to the fluorescent uncomfortable lobby area.
When the Joker's character is under pressure (performing at the comedy club) there is a harsh light directed at him, red/orange lamps are dotted around the scene to detract from the audience and focus attention on him. This light shows how exposed his character is to criticism/rejection from the crowd. Throughout the film, complimentary yellow and cyan tones play off each other to draw attention and create a distinct atmosphere, the 'green spike' of these colours mixing adds an 'off' quality designed to keep the viewer slightly uncomfortable/on edge. Red highlights shows urgency, passion or fear and helps the viewer to understand the Joker's mindset. His signature outfit also incorporates red, yellow and green which reaffirms his identity.
The left image shows the difference between pre and post composite, other than the differences in scene composition you can see there is a colour grade applied to the shot. This cyan light with hints of yellow to contrast/compliment and draw attention to the building (along with the tracked Arkham Hospital sign, ambulance and vacant space in front of the character)
