Colour Reproduction in Electronic Imaging Systems

Photography, Television, Cinematography

Michael S. Tooms

• Publisher: Wiley
• Year: 2015
• ISBN:
  9781119021773
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

With the move of cinema away from film, the adoption of electronic-based production throughout all media is now complete. In order to exploit its advantages, the accurate definition, measurement and reproduction of colour has become more important than ever to achieve the best fidelity of colour reproduction.

This book is concerned with providing readers with all they need to know about colour: how it is perceived and described, how it is measured and generated and how it is reproduced in colour systems. It serves as both a tutorial and a reference book, defining what we mean by colour and providing an explanation of the proper derivation of chromaticity charts and through to the means of ensuring accurate colour management.

Key Features:

• Addresses important theory and common misconceptions in colour science and reproduction, from the perception and characteristics of colour to the practicalities of its rendering in the fields of television, photography and cinematography
• Offers a clear treatment of the CIE chromaticity charts and their related calculations, supporting discussion on system primaries, their colour gamuts and the derivation of their contingent red, green and blue camera spectral sensitivities
• Reviews the next state-of-the-art developments in colour reproduction beyond current solutions, from Ultra-High Definition Television for the 2020s to laser projectors with unprecedented colour range for the digital cinema
• Includes a companion website hosting a workbook consisting of invaluable macro-enabled data worksheets; JPEG files containing images referred to in the book, including colour bars and grey scale charts to establish perceived contrast range under different environmental conditions; and, guides to both the workbook and JPEG files

Part 1
Colour – Perception, Characteristics and Definition

Introduction

Before the subject of colour reproduction can be addressed, it is important to first arrive at a common understanding of colour. Thus Part 1 is dedicated to explaining what colour is, how it is perceived, how it is characterised and how it is defined.

For the author of a book of this nature, which deals with a topic we all know something about but which inevitably extends into more advanced areas, it is important to know where to start. After much thought based upon the experience of many discussions about colour with a wide range of people from family and friends to those in the business of colour reproduction, it was decided to start at the very beginning, since unfortunately misconceptions about colour are often taught even within schools. Thus Chapter 1 commences with the basics of the perception of colour and colour naming (a minefield (Berlin & Kay, 1969)) in order to ensure that as the more advanced concepts are introduced all readers are at ease with the basics and the language used to describe the various parameters of colours in this field.

This chapter then goes on to introduce how the eye–brain complex perceives light and colour both in terms of its contrast range and how the overall spectral response of the eye at normal lighting levels is comprised of three different types of receptor, which respond to light in different parts of the spectrum.

In Chapter 2, the spectral responses of the eye are investigated further to explain how by using three primary colours a large proportion of the colours that can be perceived by the eye can be simulated by a mix of appropriate amounts of these primaries. The positioning of these primaries in the spectrum to optimise the size and position of the gamut of colours which can be simulated is explored and the perceived ambiguity relating to which colours are the primaries for both light sources and pigments is addressed and hopefully eliminated.

Grassman's law regarding the behaviour of the eye to linearly add the components of broad spectral bands of colours is used as the crucial basis for explaining the rules for mixing colours, which is fundamental to the process of colour reproduction. Examples of the exploitation of this rule are given in several illustrations from the two-dimensional colour triangle to the three-dimensional colour space.

The preferred terms for describing the various parameters of colour are defined together with the terms in common use and reference is made to the manner in which some of these terms are used incorrectly and thus ambiguously in common speech.

The requirement to define colours in terms of categorising them in a manner which enables workers in colour to exchange information about colour in an unambiguous fashion is explained by reference to an example system of cataloguing a broad range of colours which explores virtually the full gamut of colours the eye can perceive.

Finally an abbreviated reference is made to the effect of the quality of illumination on the perception of colours in a scene, a topic which is explored in more depth in later chapters.

An in-depth understanding of the topics in Part 1 prepares the reader for addressing the material in Parts 2 and 3.

1
The Perception of Colour

1.1 Introduction

Before addressing the reproduction of colour it is essential to have firmly based ideas about what colour is, its spectral characteristics, the way it is described differently by different people and the importance of a common naming nomenclature. Thus this chapter describes how colour is perceived, and how it is unambiguously characterised, both in terms of the quantitative and qualitative responses it evokes in the eye.

The sensitive elements of the eye at normal levels of illumination are identified and characterised both in terms of their overall sensitivity and in terms of their spectral responses.

1.2 Setting the Scene

To introduce colour as a subject for study immediately presents one with a problem. In contrast to other subjects we may decide to investigate, we all have preconceptions as to what colour is. We think we already know much about colour, we have experienced it from early childhood, colour names crop up in speech on a regular basis, we have probably been taught at school how to mix colours to obtain a wider range than those available in the paint box and almost certainly at some stage we have been introduced to the concept of primary colours as the basis of obtaining a wide range of colours from the mixture in varying amounts of just three distinctly different primary hues. We will be formally defining the parameters which are used to describe the various aspects of colour later. For the present, however, the hue of a colour describes whether it is, for example, green, yellow or violet.

However the manner in which we perceive colour, though at an overview level not particularly complex, is just complex enough to require a level of attention beyond that which many of us have been prepared to give on a casual basis. Experience has shown that as a result there is widespread confusion about how colour is perceived.

One of the problems associated with initial considerations of colour perception is the naming of colours and the manner in which we differentiate colours of various hues through the spectrum. The following four paragraphs on unitary hues adapted from the work of Ray Knight provide a sound basis on which to commence consideration of this topic.

As we step through the visible spectrum from red to violet we pass a considerable number of quite distinct hues. A listing might read as: red, orange, yellow, green, cyan or turquoise, blue and violet. (Purple and magenta hues do not appear in the spectrum.) Because these seven colours continuously blend into each other we perceive many more than these seven hues, and certainly more hues than we have distinct colour names to identify them with.

Of the seven fundamental colours named above, only four are truly distinct and to these we can add black and white which together make up a group called psychological colours or, when hues only are being referred to, as unitary hues, attributed to Ewald Hering (1834–1918), which are red, yellow, green and blue. These four important colours, share the distinction that each one can be described without reference to the other three, or any other colour. Consider yellow, for example. To find a pure yellow without a hint of either adjacent colour means we look for a yellow with an absence of green and an absence of red – perhaps chrome yellow. Such a hue can be found, but not so with orange or purple and some other hues. Orange has within it an element of yellowness and redness, and purple ha...

Table of contents

• Cover
• Title Page
• Copyright
• Preface
• About the Companion Website
• Introductions
• Part 1: Colour – Perception, Characteristics and Definition
• Part 2: The Measurement and Generation of Colour
• Part 3: The Concepts of Colour Reproduction
• Part 4: The Fundamentals of Colour Reproduction
• Part 5: The Practicalities of Colour Reproduction – Television, Photography and Cinematography
• Appendices
• References
• Index
• EULA