Understanding Color Management

Abhay Sharma

• Publisher: Wiley
• Year: 2018
• Print ISBN: 9781119223634
• eBook ISBN: 9781119223689
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

An accessible but technically rigorous guide to color management for all users in all market segments

Understanding Color Management, 2 nd Edition explains the basics of color science as needed to understand color profiling software, color measuring instruments, and software applications, such as Adobe Photoshop and proofing RIPs. It also serves as a practical guide to International Color Consortium (ICC) profiles describing procedures for managing color with digital cameras, LCD displays, inkjet proofers, digital presses and web browsers and tablets. Updates since the first edition include new chapters on iPads, tablets and smartphones; home-cinema projection systems, as well as, with the industrial user in mind, new additional chapters on large-format inkjet for signage and banner printing, flexography, xerography and spot color workflows.

Key features:

• Managing color in digital cameras with Camera Raw and DNG.
• Step-by-step approach to using color management in Adobe Photoshop CC.
• M0, M1, M2 instrument measurement modes explained.
• Testing of low cost, iPhone color measuring instruments.
• Updated to include iccMAX (Version 5.0) ICC profiles.
• G7 calibration explained with practical examples.
• Conventional printing conditions described - SNAP, GRACoL, SWOP, Fogra, CRPC.
• New sections on Pantone EXTENDED GAMUT Guide.
• Introduction to XML for color management applications.

Understanding Color Management, 2nd Edition is a valuable resource for digital photographers, keen amateurs and end-users, graphic designers and artists, web masters, production and prepress operators and supervisors, color scientists and researchers, color consultants, and manufacturers. It is a must-have course text for college and university students of graphics arts, graphic communications, digital photography, print media, and imaging arts and sciences.

The Society for Imaging Science and Technology (imaging.org) is an international professional society whose mission is to keep members and others aware of the latest scientific and technological developments in the greater field of imaging. A major objective of the Wiley-IS&T series is to advance this goal at the professional level. The broad scope of the series focuses on imaging in all its aspects, with particular emphasis on digital printing, electronic imaging, image assessment and reproduction, image archiving and preservation, color science, pre-press technologies, and hybrid imaging systems.

1
Introduction

Objectives

• Explain and define color management.
• Describe the older, closed-loop method of color control.
• List the activities of the International Color Consortium (ICC).
• Describe the three Cs of color management – calibration, characterization and conversion.
• Introduce RGB/CMYK colorspaces and Yxy/L^*a^*b^*.
• Introduce typical color management workflows.
• Describe the benefits of a color management system.

1.1 Why Do We Need Color Management?

What is color management and why do we need it? Why can’t we just use a digital camera to take a picture, view the image on a display, print it out, and have the color match throughout? The answer is that every imaging device is different and every device has its own particular characteristics.

To understand device characteristics, consider an analogy of making microwave popcorn, Figure 1.1. Through trial and error, it is possible to determine that a home microwave needs, for example, exactly two minutes to pop all the kernels without burning any. For a higher wattage, office microwave however, two minutes is too long, and it is determined that the cook time must be adjusted and reduced to one-and-a-half minutes. In a student apartment, using a weak mini-microwave, it is determined that three minutes is needed to create the perfect snack. In all instances we can achieve the same result – a perfectly popped bag of popcorn – but we must adjust the cooking time to take into account the wattage and settings of each microwave, in other words, the characteristics of each device.

Figure 1.1 Microwave popcorn needs different cook times on different appliances. Similarly different printing systems require different pixel instructions – color management is all about creating different instructions to get the same color on different devices.

In digital imaging, we may have an image with a yellow lemon, Figure 1.1. We seek to create this yellow color on different devices. Each printer prints in a different way, with different ink or toner and each device may use different media. To create this yellow color on different devices we must take into account the characteristics of each device.

In the same way that we adjust the cooking time of popcorn to accommodate the characteristics of each microwave oven, similarly we must adjust the printing instructions to take into account the characteristics of each printing system.

The amount of ink is expressed in units of percent, such as 40%, 50%, 60%, etc. (In this context % is simply an amount and not a percentage.) In Figure 1.1, an inkjet proofer may need 80% of yellow ink, while a large format device may have a very strong yellow ink set, so it may need only 76% of yellow ink to create the same color. A digital press may require 89% of yellow toner to create the same “lemon yellow”.

So we see that in order to achieve the same color on different devices it is necessary to send different instructions to each device. In the case of popcorn it may be easiest to determine the required cooking time simply via trial and error, but for an image we need a more sophisticated approach as we must consider not just yellow, but green and blue and orange and all the other colors that can be present in an image. And of course we must extend the process beyond printers to include any device in a color imaging system, including images viewed in a web browser, or a tablet device, or printed using an offset printing press, etc. Color management is a technology that enables the computation of appropriate pixel instructions on a device by device basis.

Color management is a digital technology framework that can be used to compute device-specific instructions and thereby control color among different devices in an imaging system. Color management is defined as the use of hardware, software, and processes to control and adjust color among different devices in an imaging system.

Color management is not just the technology, it is not a physical item on a store shelf that you can go and buy, color management is all about systems, processes, software, measuring instruments – a whole philosophy – a systematic framework for color control – a way of life!

This chapter provides an introduction to color management, what it is, and how it works.

1.2 Closed-loop Color Control

A fundamental issue with color imaging is that each device behaves differently, which means that we cannot send the same pixel values to different devices; we must adjust the pixel values in order that they are appropriate for each device. There are two ways of making these adjustments, the traditional way is called closed-loop color, and the new way is open-loop color, more commonly referred to as color management.

Affordable devices for color imaging are a relatively recent development that have come about because cheaper digital systems have brought the technology within the reach of the mass market. During the 1970s and 1980s, digital color was the preserve of high-end systems such as those sold by Crosfield Electronics, Hell, and Dainippon Screen. The same manufacturer would provide a color imaging suite that included the monitor, software, scanner, proofer, and so on. These were closed-loop systems in which all devices were designed and installed by one vendor.

An example of a closed-loop system is shown in Figure 1.2. The image was always acquired from a photographic scanner (perhaps a drum scanner), it was always displayed on the same monitor, and the images were destined for one type of print process, e.g. an offset print condition, that was emulated by a proprietary proofing system such as ColorArt or Chromalin. In this closely controlled situation it was relatively easy to obtain the color we wanted. However, two important conditions had to be met: a fixed workflow and skilled personnel.

Figure 1.2 In the old days, digital color was the preserve of high-end systems, where the same company, such as Crosfield Electronics, would provide a color imaging suite that included a drum scanner, monitor, software, and proofing system.

In closed-loop systems it was necessary to have a trained scanner operator. Through many hours of use, the operator would gain knowledge about the characteristics of a particular scanner and the required tone curve corrections needed. Images were acquired directly into cyan, magenta, yellow, and black (CMYK), as appropriate for a known print condition.

To obtain optimum results, the operator generated a set of actions that were necessary to apply to scanned images. Typically, this set of corrections would vary depending on such things as whether the image was low key or high key, whether it had dominant skin tones, which customer the job was for (and their color preferences), and how the job was to be printed. Color corrections were based on the operator’s experience, and the operator would use CMYK values shown by a dropper tool to make adjustments, Figure 1.3.

Figure 1.3 In closed-loop systems experienced operators edited images not on visual appearance, but using CMYK pixel values – this required considerable experience. Image shows C-scan software from FFEI.

Along with a skilled operator, the other requirement of a closed-loop system was a fixed workflow. That is, it was necessary to know where the image came from, how it would be viewed, and how it would be printed. The relationship between devices was learned through a lengthy, iterative process, and it was not easy to swap devices. If images arrived from a different scanner system, or were to be sent to a different printing configuration, a job would have to be reworked.

There were other issues with this way of working. The image edits were stored in proprietary fi...

Table of contents

• Cover
• Title Page
• Copyright
• Dedication
• Foreword to 2nd Edition
• Foreword to 1st Edition
• Preface
• Acknowledgments
• 1 Introduction
• 2 Principles of Light and Color
• 3 Color by Numbers
• 4 Measuring Instruments
• 5 Inside Profiles
• 6 Managing Color in Digital Cameras
• 7 Monitor Profiles
• 8 Press and Printer Profiling
• 9 Spot Colors & Expanded Gamut Printing
• 10 XML and Color Management
• 11 Color Management in Photoshop
• A Appendix
• Index
• End User License Agreement