Colour in Profile

BEFORE EVEN GETTING INTO PRINTED BEHAVIOURAL QUIRKS CAUSED BY THE USE OF DIFFERENT INKS ON DIFFERENT PAPERS, OR HOW THE SAME INKJET DEVICE MAKE AND MODEL CAN PERFORM DIFFERENTLY UNDER CHANGING ENVIRONMENTAL CONDITIONS, LIKE DIFFERING HUMIDITY LEVELS OR TEMPERATURES, IT IS WORTH NOTING TOO THAT COLOURS LOOK DIFFERENT UNDER VARYING VIEWING CONDITIONS.

This variable is known as metemerism and essentially points to the fact that an optimum digital inkjet colour proof system must deliver 4,000-6,000 colours in a gamut to match offset printing. A seemingly short order if you consider that the human eye can distinguish up to ten million colours in its gamut. But still a significantly tall technology order, even given the recent advances in inkjet.

This is where ICC profiling comes in. The International Colour Consortium (ICC) was established in 1993 by eight industry vendors for the purpose of creating, promoting and encouraging the standardization and evolution of an open, vendor-neutral, cross-platform colour management system architecture and components. The resultant ICC profile format essentially provides a cross-platform device profile format that can

be used to translate colour data created on one device into another device's native colour space. Furthermore, embedded ICC profiles allow users to ‘transparently’ move colour data between different computers, networks and even operating systems without having to worry if the necessary profiles are present on the destination systems.

ICC profiles permit tremendous flexibility to both users and vendors. For example, it allows users to be sure that their image will retain its colour fidelity when moved between systems and applications, assuming the new system is capable of reproducing all the original colours. While it allows an inkjet printer manufacturer to create a single profile for multiple operating systems.

The specification divides colour devices into three broad classifications: input devices, display devices and output devices. For each device class, a series of base algorithmic models are described which perform the transformation between colour spaces. These models provide a range of colour quality and performance results which provide different trade-offs in memory footprint, performance and image quality. The device profiles obtain their openness by using a well-defined reference colour space and by being capable of being interpreted by any ICC operating system or application that is compliant with the specification.

17