Definition and use of the ISO 12640-3 reference colour gamut

Abstract

While a number of color encodings are specified for imaging applications, neither the group developing the ISO 12640-3 CIELAB standard color image data, nor the International Color Consortium (ICC), found a suitable existing specification for a large gamut reflection print reference medium. Such a specification was needed as a color rendering target for the creation of the CIELAB standard images. Thus, the ISO working group started to develop the reference color gamut specified in the Draft International Standard ISO 12640-3.

The project aim was to produce an international standard (ISO) for the graphic arts industry to govern the evaluation of colour management systems and is a development of an earlier working document that will ultimately lead to the definition of the standard.

The standard itself provides standard test images, encoded as 16 bit CIELAB data, referenced to D50, the standard viewing illuminant for graphic technology and photography as defined in the earlier standard ISO 3664. This new standard provides a set of images, together with appropriate statistics, that can be used for the evaluation and development of colour management systems for the graphic arts.

In order to create the standard it was necessary that well-defined colour gamuts be specified, so that they could be properly interpreted in colour reproductions systems. Work was undertaken by the authors to determine a sensible gamut for the images by analysing data referring to the gamut of ‘real world’ colours as well as the colour gamut of printers. The resultant new gamut can be thought of as the gamut of ‘real world’ surface colours.

Tony Johnson

Research Interests
• Colour Imaging
• Gloss
• Colour measurement
• Image Processing
• Printing Technology

Current Research

Since the end of 2004 I have largely retired but prior to that I spent over 30 years working in colour imaging research for the printing industry. I helped develop many colour and image processing algorithms for electronic imaging and undertook research in many aspects of colour reproduction by printing. I was also heavily involved in international standardisation for printing for many years.

During my last 10 years prior to retirement, as well as being a Professor at the LCP undertaking both research and teaching in colour imaging, I undertook consultancy work in colour imaging. Prior to that I worked in research for both Pira and Crosfield Electronics who, at that time, was one of the market leaders in electronic colour imaging.

I am in the process of publishing papers based on my research activity prior to retirement, dealing with the measurement of gloss and its effect on colour management. My time at LCC is now spent supervising research students. Currently I am supervising 5 postgraduate students working on various aspects of colour imaging, including colour management on non-paper substrates, colour difference measurement for complex images, colour image quality measurement, n-colour printing.