Ensuring color consistency in commercial printing and packaging is critical for maintaining brand integrity and meeting customer expectations. One of the most effective ways to achieve this is by leveraging quality control software that utilizes precise color tolerancing methods. In this blog, we will explore different tolerancing techniques and how QC software enhances accuracy in color control.
The Challenge of Visual Color Assessment
Many assume that visual inspection alone is sufficient for evaluating color accuracy. However, our eyes can be deceived from various factors such as retinal fatigue, background effects, poor color memory, color deficiency, and lighting conditions. Even trained professionals can experience discrepancies when evaluating color visually. (Wondering if you have some form of color vision deficiency? Take the test!)
To overcome these challenges, physical color targets such as printed samples, ink drawdowns, and standardized color references are used. However, these too have limitations, including:
- The need for precise reproduction to avoid inconsistencies.
- Variability due to lighting conditions and subjective perception.
- Durability issues, as samples can fade or become contaminated over time.
- Lack of numerical data for precise color evaluation.
This is where quality control software becomes invaluable, offering precise numerical color measurement to eliminate subjectivity.
Measuring Color Differences with Color Spaces
Color measurement relies on color spaces, which map colors using specific coordinates. Two commonly used models in QC software include:
- L*C*h* Model: Similar to how longitude, latitude, and altitude coordinates tell you exactly where you are on Earth, this model uses three values to define where a color sits within a range, including lightness (dark to light), chroma (dull grey to vivid), and hue angle (position on the color wheel).
- L*a*b* Model: Like LCH, L represents lightness, but instead of chroma and hue, two different axes are used to describe color shifts. The a-axis moves between green and red—negative values shift toward green, while positive values move toward red. The b-axis moves between blue and yellow—negative values are more blue, while positive values are more yellow. If both a and b are at zero, the color is perfectly neutral along the lightness axis.
By defining a color within these spaces, color control software can accurately quantify differences between colors.
Understanding Delta E and Tolerancing Methods
Delta E is used to measure color differences, which calculates the distance between a target color and a sample color. The higher the Delta E value, the more noticeable the difference. Tolerances determine acceptable variations before a color is considered out of specification.
Types of Delta E Calculations:
- Delta E*ab or Delta E76 (Unweighted Method): The original Delta E formula, which applies equal weighting in all directions. While still used in some applications, it does not always align well with human perception.
- Delta E CMC (Weighted Method): Introduced to better match visual perception by assigning different weightings to hue, chroma, and lightness. When a color appears significantly different to the eye, this model should also reflect that difference numerically.
- Delta E 2000 (Industry Standard Weighted Method): The most widely used method today, incorporating improved weighting factors to provide more accurate color tolerancing for both spot and CMYK inks.
The Science Behind Weighted Color Tolerancing
The human eye is more sensitive to hue shifts than to changes in chroma or lightness. Because of this, color tolerancing methods apply stricter limits to hue while allowing more flexibility in chroma and lightness. This approach helps ensure colors appear consistent to the human eye, even when minor variations exist.
Additionally, we tend to notice shifts in less saturated colors—such as grays and pastels—more than in bold, vibrant hues. To compensate for this, tolerancing methods create smaller ellipsoids (tighter tolerances) for duller colors and larger ellipsoids (more flexibility) for vivid ones.
Customizing Tolerances with Weighting Factors
Some tolerancing methods allow users to fine-tune the shape of tolerance ellipsoids using weighting factors. This customization is useful for adapting to industry-specific needs or unique visual requirements.
For example, Delta E CMC tolerancing applies a ratio between lightness (L) and chroma (C), commonly set at 2:1. This means twice as much variation is allowed in lightness as in chroma, aligning with how the human eye perceives color differences. Delta E 2000, on the other hand, integrates this perception-based weighting directly into its mathematical model, typically using a balanced 1:1:1 approach that is not modified.
Tolerancing in Real-World Applications
Different printing and color validation processes require specialized tolerancing methods.
- G7 for Gray Balance: The G7 methodology adjusts Cyan, Magenta, and Yellow to create a neutral gray, ensuring proper tonality and balance. It uses:
- Delta L: Measures lightness differences without factoring in color to assess tonality.
- Delta Ch: Measures color differences without considering lightness to assess color balance.
- Flexographic Ink Validation: Flexographic printing introduces additional challenges due to variations in ink formulations, substrates, and specific performance requirements like food safety or fade resistance. A key factor in flexo ink validation is ensuring the ink’s hue angle aligns with the intended target. To achieve this, ISO specifications reference Delta Hab, which evaluates hue accuracy.
Choosing the Right Tolerancing Method
Selecting the appropriate tolerancing method depends on the specific application and communication requirements. Key best practices include:
- Clear Communication: Document and share tolerancing methods and weighting factors with all stakeholders.
- Follow Industry Standards: Unless specified otherwise, Delta E 2000 (with a 1:1:1 weighting ratio) is the most reliable method.
Understanding Acceptable Tolerances in Print Production
When it comes to setting acceptable tolerances in print production, it's not just about selecting a method—it's about establishing realistic expectations based on process capability. Tolerances should be a mutual agreement between the buyer and the print supplier, as different printing processes have varying levels of consistency.
Industry Tolerances vs. Press Fingerprint Data
Many print suppliers follow industry-standard tolerances, often using Delta E 2000 to measure color differences.
- CMY inks: Tolerance < 3.5 Delta E 2000
- Black ink: Tolerance < 5 Delta E 2000
- Spot inks: Tolerance < 2 Delta E 2000
If the CMYK target values are based on their own press fingerprint data, the tolerances will be tighter for the process inks.
- CMYK inks: Tolerance < 2.5 Delta E 2000
- Spot inks: Tolerance < 2 Delta E 2000
However, not all printing conditions allow for tight tolerances. Various factors—such as substrate type, printing method, and press variability—can introduce additional shifts in color. In such cases, a statistical approach can help assess and define realistic tolerances. By consistently measuring and evaluating color data, print professionals can:
- Identify when the process is out of control
- Investigate root causes of inconsistencies
- Determine whether adjustments can be made or if tolerances need to be widened
If the variability is controllable, tolerances can remain tight. However, if the fluctuations are inherent to the printing process and cannot be controlled, it may be necessary to adjust tolerances accordingly.
Why Use QC Software for Color Control?
Given the complexities of color perception and tolerancing, quality control software is essential for achieving accurate, consistent results. Here’s how it helps:
- Standardized Color Evaluation: QC software eliminates subjectivity by providing numerical data rather than relying on visual judgment.
- Advanced Tolerancing Models: It supports industry-standard tolerancing methods such as Delta E 2000, ensuring compliance with brand quality programs.
- Improved Communication: By clearly defining tolerancing methods and weighting factors, QC software minimizes discrepancies between printers and print buyers.
- Efficiency and Accuracy: Automated measurements reduce errors, save time, and improve workflow efficiency in color verification.
Achieve Color Consistency with the Right QC Software
Color accuracy is a crucial factor in commercial printing and packaging, and quality control software plays an integral role in maintaining consistency. By using advanced QC software, like ColorCert or MeasureColor, printers and brand owners can achieve more reliable and precise color tolerancing, reducing errors and improving overall print quality. Whether working with spot colors, CMYK inks, or specialized applications, leveraging the right software ensures that every print meets the highest standards of color accuracy.
Ready to take your color evaluation to the next level? To learn more about X-Rite quality control software for print and packaging applications, get in touch with our Color Experts.
