ICC and DeviceLink profiles
Colour management for print and media companies
Digital colour management
Colour management systems use device-neutral colour descriptions (device connection spaces / DCS) and device-neutral profile connection spaces / PCS). The task of a colour management system involves converting the device-dependent colour descriptions (the input and output devices) back and forth using the device-neutral exchange colour space. This allows each device in a colour management system to represent approximately the same colours.
Practical example for colour management
the device profile generally used is the ICC Profile. The colour models involved are frequently the RGB colour model (for digital cameras and monitors) and the CMYK colour model (for printers). The colour spaces involved (RGB and CMYK) are elements of the colour models mentioned.
The device-neutral CIELab colour space, in this case, serves as the link between the other colour spaces.
Colour-safe communication with IPM
The team at IPM offers you practical assistance when it comes to creating and integrating ICC or DeviceLink profiles, whether it involves optimisation of your digital printing press, offset printing press or proofing system.
The optical brighteners that are found in almost all overlay materials (of weak to high intensity) also need to be taken into account.
They are the reason why, despite excellent settings of the machine parameters, visible differences can still occur when it comes to coordination. This then raises the question as to which “setting screws” the user can turn to achieve an improvement in production. This is where the engineers from IPM come on board.
Why are colour profiles important?
Just as every human perceives colour differently, devices – at least classes of devices – also have different colour spaces in which they register or represent colours. This type of individuality is caused by design differences and fluctuations in production.
Colour profiles are able to reflect the colour data of a device class or the individuality of a specific device. The standard format for colour profiles was developed by the ICC (International Color Consortium) and standardised internationally in the ISO 15076 standard. Every device (monitor, digital camera, scanner, etc.) involved with the conversion needs its own profile. It contains conversion tables or calculation parameters that are used to convert the colour from or into the PCS (profile connection space). XYZ and LAB are primarily used as the PCS. In terms of the reason for their use, a distinction is made between input profiles (RGB → PCS), output profiles (PCS → RGB or CMYK) and Devicelink profiles, which permit direct gamut mapping without any need for a diversion via a PCS between two CMYK colour spaces.
In terms of the internal structure, a distinction is made between matrix profiles and LUT (look up table) profiles. Matrix profiles are the profiles of choice for devices with colour behaviour that is dependent on relatively few influences and which can therefore be described in an adequately effective way in the form of a 3 x 3 conversion matrix, for example. The file size of matrix profiles is relatively small (a few kilobytes).
LUT profiles are used for devices with colour behaviours that are influenced by a number of factors and which are too complex to be described adequately by a simple matrix transformation.
LUT profiles can be up to several megabytes in size.
It must be borne in mind that a profile only applies for a specific state of the device in question. So, for example, if the paper type is changed from white to yellow, the same CYMK values would result in different colours. The same goes for monitors if the brightness control is adjusted, for instance.
Step by step to the colour profile:
Creation of a colour profile
Profiles are created on the basis of colour measurement. During this process, colours whose exact colour values are known are reproduced by the device (monitor, printer) or measured (scanner) and then compared with the known values. This can give rise to the gamut that describes a device’s ability to reproduce a colour.
One of the most common tasks is the conversion of old CMYK data into a “different” ISO standard. Many printshops have historically also had house standards for the proof, in addition to the ISO standards. Optimised DeviceLink profiles are the best option for converting old CMYK data so that they achieve the same colour impression on a proof based on the ISO standard as they do on a proof based on the house standard.
DeviceLink profiles from IPM
DeviceLink profiles, especially in the process conversion from CMYK to CMYK, targeted ink application restriction (with preservation of the separation properties) and in the optimisation of data, have proven their capabilities in terms of printing ink savings. If complete print data with image, text and vector objects (e.g. as PDF) needs to be converted, DeviceLink profiles should be used since these offer targeted management of the colour structure in order to protect certain colours or colour combinations.
The best example is black structure, which can be preserved over the conversion using a DeviceLink profile. You can be reassured that a purely black-structured text or a technical tone (e.g. a shadow) will be made up entirely of pure black even after conversion.
Another advantage of DeviceLink technology lies in the fact that colour data is only changed where it is effectively required. If no adaptation is needed, the separation is not changed – a point that is simply impossible with ICC profile-based conversion.
DeviceLink profiles can be used for process conversion, process adaptation, standardisation of the colour structure and for colour saving.
Colour management and the digital exchange of data between documents require unique relationships between the digital tonal values and the printed colour values. The digital tonal values are generally presented as CMYK process colour values.
In packaging printing, individual process colours can be swapped for other, product-specific colours. The printed colour values depend on the printing process (sheet-fed offset printing, web offset printing, intaglio printing, screen printing), the process standard (colouring, dot gain) and materials (printing stock, ink) used.