The base for Colourspace
- Ximena
- 4 may 2023
- 2 Min. de lectura
A colourspace is a set of parameters that define a particular device's colour capabilities or are stored in a digital file, generally outlined by three colour primaries and a white point.
Each monitor and file can display/store a specific range of colours, known as its colour gamut.
For example, suppose you have two displays with different colour spaces, and you look at the same file on different devices. In that case, the output from the displays will be different as one device may not be physically capable of displaying the same colours as another display.
Using specialized hardware, you measure the various aspects which make up a displays output that can be simplified to its red output, its green output, its blue output, known as its colour primaries, and its white point, which is the point of the purest and lightest white in a colourspace.
However, just having these values doesn't help much, as they can all be arbitrary depending on the hardware used to measure them, so standards are used to make all the values comparable.
The most common standard is the CIE 1931 Chromaticity Diagrams.
This CIE 1931 Chromaticity standard diagram is the most commonly used standard to compare colour spaces of displays and files for the human eye. Each colourspace will cover a range from this diagram, with some being bigger than the CIE range. However, utilizing colours beyond this spectrum holds little significance since the human eye cannot perceive them.
The image below shows some examples of different colour spaces when compared to the CIE 1931 Chromaticity standard, such as ACES2065-1, ACEScg, DCI-P3Rec, Rec 709 and Rec 2020:
The colour primaries define the points of the triangles for these colour spaces, and the dot in the middle of the triangle is the white point.
For example, the Rec 709 primaries and white point as defined by the ITU R Bt.709-6 are:
These colour spaces are then used to calculate how every value of RGB should look to the average human eye.
Colour spaces are standards that cannot be changed when defined. So sRGB, for example, was developed by HP and Microsoft for use on CRT monitors, printing and the internet, and as such, has a range of values that meet what a CRT monitor can output.
However, as technologies develop, users need access to a broader range of colour values, so newer standards are developed to encompass those requirements, such as rec2020 for HDR content.
Other colour spaces are defined by the physical attributes of the recording devices, so RED, for example, has a range of colour spaces for their various camera models depending on the capabilities of the camera's hardware.
Camera manufacturers often utilize their own unique log curves and RGB color space specifications. For instance, ARRI Alexa cameras commonly use ALEXA Log C and ALEXA Wide Gamut RGB, while RED cameras tend to use RED Log Film, REDcolor, or DragonColor.
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