A model of consistent colour appearance Gregory High, PhD Candidate The Norwegian Colour and Visual Computing Laboratory Faculty of Computer Science and Media Technology Norwegian University of Science and Technology Gjøvik, Norway gregory.high@ntnu.no http://www.colourlab.no
Personal background Background in graphic design and print production Responsibility for colour management, proofing and pre media in Design Studios and Advertising Agencies Member of UK TC 130 technical advisor group MSc Digital Colour Imaging in 2008 at London College of Communication Joined the ColourLab in November 2015
Introduction The project objective is to build a model of consistent colour appearance for graphic arts and colour display applications. The aim is to facilitate colour reproductions across different output media that create, as close as possible, an appearance match relative to the context and viewing conditions of each medium. The scope of the project is limited to colour appearance; other appearance attributes are excluded.
Commercial Context Print Digital print technologies capable of larger (and different) colour gamuts compared to traditional print processes There is an expectation to use the available gamut of each printing device These new technologies are expected to be used alongside traditional print technologies
Commercial Context Display Challenge from new display technologies and encodings Rec. 2020 allows for wide gamut colour encoding using three monochromatic primaries Still no agreed method of consistent gamut mapping or appearance mapping across output devices Source: avsforum.com
Current Research Activity CIE Reportership R8 13 Common Colour Appearance Proposed CIE Technical Committee Consistency of Colour Appearance
Current Research Activity Aims to differentiate itself from previous work on colour difference and gamut mapping Concerned with similarity between a suite of (print) reproductions, with or without a reference original How to assess similarity? Which appearance attributes to include? Source: Craig Revie, CIE R8 13 Common Colour Appearance Focus Group
Areas of interest The observer s relationship with multiple images Mixed adaptation to substrate white points Lightness scaling across media Hue preservation and chroma scaling issues A metric of colour (dis)similarity A model of common colour appearance
The observer s relationship with images What makes a consistent set of images? Gestalt like organisation is an important parameter (proximity, similarity, continuation) Physical interaction with print is very different to display
Mixed adaptation issues Mixed adaptation to substrate white points or display white points Examine a Graphic Arts application of optimised mixed or partial adaptation Investigate image content as a parameter of colour appearance prediction
Mixed adaptation issues Paper at Electronic Imaging 2017 Content dependent substrate adaptation in a soft proofing experiment Work needs to be extended to include hard copy patches and images Mean Degree of Adapta on D (CI=95%) 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 100.00 0.10 0.20 Neutral Patches Degree of adjustment D for different L* lightness levels 0.30 Rel. Lightness L* of neutral patches
Lightness scaling issues Lightness scaling for reproduction images where media dynamic ranges are different Print Density NPD NPD vs Input Cyan Tone Value 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 0 10 20 30 40 50 60 70 80 90 100 Cyan Value Input Tone Value Series1 Series2 Series3 Series4 Series5 Series6 Series7 Can lightness scaling to be optimised for simultaneous viewing conditions? Some industry preference for harmonisation of highlights at the expense of compressed shadow detail Source: David McDowell, CIE R8 13 Common Colour Appearance Focus Group
Hue preservation and Chroma scaling Much previous work on colour gamut mapping Traditional print technologies have relied on intrinsic similarities of gamut shapes between different media to ensure similarity of appearance Source: Characterized Reference Printing Conditions, ISO/PAS 15339 Graphic technology Printing from digital data across multiple technologies
A useful metric A metric of colour appearance dissimilarity Soft metrology Image difference Medium gamut constraints Extensible framework other appearance attributes may be added
The model A model of Consistent Colour Appearance, including: print application display application Scope limited to colour appearance (other appearance attributes are excluded)
Thank you for your attention Contact information: Gregory High Office: A252 E mail: gregory.high@ntnu.no Web: www.colourlab.no Mobile: (+44) 7775 507731