A Technical Color Guide for Printing

In the world of printing, accurate color reproduction is one of, if not the most important issues. The ability to reproduce colours precisely is critical for companies wishing to have consistent branding.. Achieving the right colors in print involves understanding color basics, managing color with precision, and employing the right tools and techniques. This article provides a comprehensive technical color guide, delving into essential components like color gamuts, color matching systems, and the role of spectrophotometers in achieving optimal color reproduction.

Understanding Color Basics

RGB vs. CMYK Color Models

In the world of color, two primary models dominate—RGB (Red, Green, Blue) and CMYK (Cyan, Magenta, Yellow, Key(Black)). RGB is primarily used for digital displays, while CMYK is the standard for print. 

Understanding the differences and best use cases for each model is important for achieving accurate color representation in the intended use.

Understanding Color Gamut and Limitations

The color gamut represents the entire range of colors that a device or color space can reproduce. Different devices and color models possess distinct ranges in available colors. For Instance RGB has over 16,000,000 colors and shades, whereas CMYK only contains around 16,000 colors.
You Can find much more in depth detail CMYK and RGB in our article titled All about colors...in regards to printing

 

Color Management Systems

What is a color management system?

A color management system (CMS) is a set of software, hardware, and processes, designed to create consistent and accurate representation of colors.

Color Profiles

These are mathematical descriptions of a printing press’ color behaviour. They define how a printing press reproduces colors, allowing the CMS to compensate for the unique color characteristics of each press. Profiles are also used for different materials the press prints onto. Further ensuring that colors will always match.

Color Calibration

Instruments like colorimeters and spectrophotometers are the most accurate and efficient tools used to calibrate and profile printers. They allow printers to create color profiles, therefore calibrating devices to ensure accurate color representation and consistency throughout the printing process.

Extending Color Gamuts with Additional Inks

Additional inks (Green, Orange, and Violet) beyond the standard CMYK, can be added to a printing press to extend the color gamut. These inks enhance the range of colors that can be reproduced, allowing for more vibrant and accurate color representation. They are only really useful when using spot colors, as CMYK colors will always print using CMYK.

Advantages and Challenges of using Additional Inks

While extending color gamuts offers benefits (as mentioned above), it also presents challenges like increased complexity and cost. 

The complexity usually comes from the creation of the spot colors, and the effort needed to print samples, then visually and digitally (using a spectrophotometer) compare how the printed color compares to the desired color. Often once the color has been set up, it is easy as printing presses can usually run automatic calibrations to ensure continued color accuracy.

The additional cost is down to both the cost of the additional ink used, as well as a reduced printing speed, and the extra maintenance required.

Spectrophotometers in Color Management

Spectrophotometers are sophisticated instruments used for precise color measurement and analysis. They can quantify color by measuring the intensity of a light beam at different wavelengths. These measurements are then used to create color profiles, as well as compare colors using a calculation called Delta E.

Color Comparison Using Delta E

In the realm of color management and color accuracy, Delta E (ΔE) is the fundamental metric used to quantify the difference between two colors. 

It provides a numerical value that represents the perceptual difference or distance between the desired color and the printed/ simulated sample color.

Understanding Delta E (ΔE)

The International Commission on Illumination (CIE) calls their distance metric ΔE
Delta E is a mathematical formula that calculates the Euclidean distance between two points in a three-dimensional color space. The latest and most accurate version of the Delta E formula is CIEDE2000. This is used worldwide, with the resulting Delta E value quantifying the color difference based on factors like lightness, chroma, and hue.

Delta E does not use the RGB or CMYK color models. Instead it uses the LAB or HSL color model. The key difference between these and RGB is that LAB/HSL covers the entire visible light spectrum.

Interpretation of Delta E Values

The Delta E value provides insights into the perceptual difference between two colors. Here's a general guide for interpreting Delta E values:

• Delta E < 1.0: Imperceptible difference. Colors are essentially identical to the human eye.
• 1.0 ≤ Delta E < 2.0: Slight difference. Some individuals may notice a subtle variation in color.
• 2.0 ≤ Delta E < 3.0: Noticeable difference. Most observers can discern a difference in color.
• Delta E ≥ 3.0: Significant difference. Colors are visibly distinct and may not meet color accuracy requirements.

Limitations of Delta E

• Delta E does not fully account for human vision variations, especially for certain colors and lighting conditions.
• It doesn't consider color preference or the context in which the colors are viewed.
• The same Delta E value can represent perceptually different differences depending on the color and region within the color space.

Pantone: A Color Matching System

Pantone is the world-renowned color matching system widely used in the printing and design industry. 

It provides a standardised way of identifying and communicating colors. Ensuring consistency across various mediums and materials.

The Pantone Matching System (PMS) uses a unique numbering system, and a set of tools such as color book/swatches. These are used by designs and brands when creating brands, then by printing companies such as Sticker it to achieve consistent color across all methods and mediums of communication.

PMS is not without its issues. Many colors in their color books, and far from achievable using standard CMYK printing methods. 

Even when including an extended ink set, ~5% of colors remain unachievable. The only way to achieve this is using older non-digital printing technologies such as litho printing. The problem with these older non-digital methods is that often, to be cost-effective, you need to print on very large volumes.