Everything About Colour
Colour is the visual perceptual property corresponding in humans to thecategories called red, green, blue and others. Colour derives from the spectrumof light (distribution of light energy versus wavelength) interacting in the eyewith the spectral sensitivities of the light receptors. Colour categories andphysical 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 beidentified numerically by their coordinates.
Because perception of colour stems from the varying spectral sensitivity ofdifferent 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 stimulatethese 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 perceptionof colour by the human eye and brain, the origin of colour in materials, colourtheory in art, and the physics of electromagnetic radiation in the visible range(that is, what we commonly refer to simply as light).
Colour Space
The colour space (or gamut) visible to humans is determined by the ability ofour visual system to detect and respond to specific wavelengths of light hittingthe fovea and it’s immediate surround.
The colour gamut of an emissive device or of a colour system is defined by theprimary colours used to construct the system.
In an additive colour system (e.g. monitors TV, projectors) the size of the colourgamut, is determined by the 3 RGB sources.
In a subtractive system (e.g. Colour Printing, Paints, dyed garments) the gamutis determined by the primary inks, dyes, or pigments used, e.g. the CMYKmodel, ECG model (Extended colour gamut CMYKOGV), etc.
What is Colour Management?
In digital imaging systems, colour management is the controlled conversionbetween the colour representations of various devices, such as image scanners,digital cameras, monitors, TV screens, film printers, computer printers, offsetpresses, and corresponding media.
The primary goal of colour management is to obtain a good match across colourdevices; for example, a video which should appear the same colour on acomputer LCD monitor, a plasma TV screen, and on a printed frame ofvideo. Colour management helps to achieve the same appearance on all of thesedevices, provided the devices are capable of delivering the needed colourintensities.
What is an ICC profile?
In colour management, an ICC profile is a set of data that characterises a colourinput or output device, or a colour space, according to standards promulgated bythe International Color Consortium (ICC). Profiles describe the colour attributesof a particular device or viewing requirement by defining a mapping betweenthe device source or target colour space and a profile connection space (PCS).This PCS is either CIELAB (L*a*b*) or CIEXYZ. There is now iccMAXwhich includes support for Spectral Data in the PCS. Mappings may bespecified using tables, to which interpolation is applied, or through a series ofparameters for transformations.
Every device that captures or displays colour can have its own profile. Somemanufacturers[1] provide profiles for their products, and there are severalproducts[2] that allow end users to generate their own colour profile, typicallythrough the use of a tristimulus colorimeter or preferably a spectrophotometer.
The ICC defines the format precisely but does not define algorithms orprocessing details. This means there is room for variation between differentapplications and systems that work with ICC profiles.
What is the International ColorConsortium?
The International Color Consortium was formed in 1993 by eight industryvendors in order to create a universal colour management system that wouldfunction transparently across all operating systems and software packages.
The ICC specification, currently on version 4.4 allows for matching of colourwhen moved between applications and operating systems, from the point ofcreation to the final print.
The main emphasis of the ICC is to define a format for ICC profiles, whichdescribe the colour attributes of a particular device or viewing requirement bydefining a mapping between the source or target colour space and a profileconnection space (PCS).
The ICC defines the format precisely but does not define algorithms orprocessing details. This means there is room for variation between differentapplications and systems that work with ICC profiles.
What does ISO standards mean?
The ISO implements its charter by way of Technical Committees (TCs). Currently, it has 834 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 112 published ISO standards, with 19 under development. 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 ofterminology, test methods and specifications in the field of printing and graphictechnology from the original provided to finished products.” The scope includes inparticular:
- 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 amedium either coloured or not (ink, etc.) to substrate, using a relief, planographic,intaglio, stencil or other image element.”