Everything About Colour

Colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Colour derives from the spectrum of light (distribution of light energy versus wavelength) interacting in the eye with the spectral sensitivities of the light receptors. Colour categories and physical specifications of colour are also associated with objects, materials, light sources, etc., based on their physical properties such as light absorption, reflection, or emission spectra. By defining a colour space, colours can be identified numerically by their coordinates.

Because perception of colour stems from the varying spectral sensitivity of different types of cone cells in the retina to different parts of the spectrum, colours may be defined and quantified by the degree to which they stimulate these cells. These physical or physiological quantifications of colour, however, do not fully explain the psychophysical perception of colour appearance.

The science of colour is sometimes called chromatics. It includes the perception of colour by the human eye and brain, the origin of colour in materials, colour theory in art, and the physics of electromagnetic radiation in the visible range (that is, what we commonly refer to simply as light).

The colour space (or gamut) visible to humans is determined by the ability of our visual system to detect and respond to specific wavelengths of light hitting the fovea and it’s immediate surround.
The colour gamut of an emissive device or of a colour system is defined by the primary colours used to construct the system.

In an additive colour system (e.g. monitors TV, projectors) the size of the colour gamut, is determined by the 3 RGB sources.

In a subtractive system (e.g. Colour Printing, Paints, dyed garments) the gamut is determined by the primary inks, dyes, or pigments used, e.g. the CMYK model, Hexachrome model, etc.

In digital imaging systems, colour management is the controlled conversion between the colour representations of various devices, such as image scanners, digital cameras, monitors, TV screens, film printers, computer printers, offset presses, and corresponding media.

The primary goal of colour management is to obtain a good match across colour devices; for example, a video which should appear the same colour on a computer LCD monitor, a plasma TV screen, and on a printed frame of video. Colour management helps to achieve the same appearance on all of these devices, provided the devices are capable of delivering the needed colour intensities.

In colour management, an ICC profile is a set of data that characterises a colour input or output device, or a colour space, according to standards promulgated by the International Color Consortium (ICC). Profiles describe the colour attributes of a particular device or viewing requirement by defining a mapping between the device source or target colour space and a profile connection space (PCS). This PCS is either CIELAB (L*a*b*) or CIEXYZ. Mappings may be specified using tables, to which interpolation is applied, or through a series of parameters for transformations.

Every device that captures or displays colour can have its own profile. Some manufacturers[1] provide profiles for their products, and there are several products[2] that allow end users to generate their own colour profile, typically through the use of a tristimulus colorimeter or preferably a spectrophotometer.

The ICC defines the format precisely but does not define algorithms or processing details. This means there is room for variation between different applications and systems that work with ICC profiles.

The International Color Consortium was formed in 1993 by eight industry vendors in order to create a universal colour management system that would function transparently across all operating systems and software packages.

The ICC specification, currently on version 4.3 allows for matching of colour when moved between applications and operating systems, from the point of creation to the final print.

The main emphasis of the ICC is to define a format for ICC profiles, which describe the colour attributes of a particular device or viewing requirement by defining a mapping between the source or target colour space and a profile connection space (PCS).

The ICC defines the format precisely but does not define algorithms or processing details. This means there is room for variation between different applications and systems that work with ICC profiles.

The ISO implements its charter by way of Technical Committees (TCs).

Currently, it has 244 TCs covering a vast array of industrial and technical issues. These TCs are invoked at the request of a group of industry representatives based on the need to address technical issues and development uniform resolutions. They usually exist only for the time necessary to develop, implement and monitor implementation. They authorise standards and their revisions by way of vote. The ability to vote is dependent on the status of the member country. Generally, Participant (P) members are allowed to vote; Observer (O) members are not. Australia is a P member with our own TC130.

The Technical Committee covering standards applicable to Graphic Arts is the TC 130: Graphic Technology. The TC130 is directly responsible for 81 published ISO standards. It has 25 participating countries and 21 with observer status. Each country has its own TC 130 which decides, if they are a Participant member, how they will vote on the contents of new standards and their subsequent revisions.

According to the ISO website the scope of the TC 130 covers "Standardisation of terminology, test methods and specifications in the field of printing and graphic technology from the original provided to finished products." The scope includes in particular:

• composition
• reproduction
• printing processes
• finishing (for example binding)
• suitability of inks, substrates and other materials used in graphic technology

Note:

Printing is defined here as a process of reproduction involving the transfer of a medium either coloured or not (ink, etc.) to a substrate, using a relief, planographic, intaglio, stencil or other image element.

"Printing is defined here as the process of reproduction involving the transfer of a medium either coloured or not (ink, etc.) to substrate, using a relief, planographic, intaglio, stencil or other image element."

TC 130 - Graphic technology
The link above above can display the current published standards and standards under development, the current total of these being 82!

ISO/AWI 19301
Graphic technology -- Colour quality management certification scheme (UNDER DEVELOPMENT)

ISO 12647-1:2013
Graphic technology -- Process control for the production of half-tone colour separations, proofs and production prints -- Part 1: Parameters and measurement methods

ISO 12647-2:2013
Graphic technology -- Process control for the production of half-tone colour separations, proof and production prints -- Part 2: Offset lithographic processes

ISO 12647-3:2013
Graphic technology -- Process control for the production of half-tone colour separations, proofs and production prints -- Part 3: Coldset offset lithography on newsprint

ISO 12647-7:2013
Graphic technology -- Process control for the production of half-tone colour separations, proof and production prints -- Part 7: Proofing processes working directly from digital data

ISO 12647-8:2012
Graphic technology -- Process control for the production of half-tone colour separations, proof and production prints -- Part 8: Validation print processes working directly from digital data

ISO 3664:2009
Graphic technology and photography -- Viewing conditions
ISO 3664:2009 specifies viewing conditions for images on both reflective and transmissive media, such as prints (both photographic and photomechanical) and transparencies, as well as images displayed in isolation on colour monitors.

Basically this is the standard for viewing conditions for colour appraisal & critical colour evaluation of offset and digital printed matter, digital proofs and digital photo 'prints'.

ISO 13655:2009
Graphic technology -- Spectral measurement and colorimetric computation for graphic arts images

ISO 2846-1:2006
Graphic technology -- Colour and transparency of printing ink sets for four-colour printing -- Part 1: Sheet-fed and heat-set web offset lithographic printing

ISO 12646:2015
Graphic technology -- Displays for colour proofing -- Characteristics

ISO/DTS 15311-1
Graphic technology -- Requirements for printed matter for commercial and industrial production -- Part 1: Measurement methods and reporting schema

ISO/DTS 15311-2
Graphic technology -- Requirements for printed matter for commercial and industrial production -- Part 2: Commercial production printing

ISO/PAS 15339-1:2015
Graphic technology -- Printing from digital data across multiple technologies --
Part 1: Principles

ISO/PAS 15339-2:2015
Graphic technology -- Printing from digital data across multiple technologies --
Part 2: Characterized reference printing conditions, CRPC1-CRPC7