Color Science Explained: Lab and LCH Color
In our previous article, we were talking about color precision. A key highlight was the Lab color space, a three-dimensional model crucial for accurate color representation in printing. Professionals rely heavily on Delta E (ΔE) to specify shades whether from the Pantone Matching System (PMS) or matching previous prints. This metric, closely linked to Lab values, ensures that colors resonate accurately, emphasizing the significance of precise color matching in conveying the right brand message and aesthetics.
It should be noted that the 3D spherical photos above are a theoretical representation only. The actual printable color space is not a perfect shape but rather a blob-like shape that very roughly can be called a sphere.
Lab and LCH color terminology are used daily in print production. It is imperative that one can discuss and understand issues with any color in both Lab and LCH spaces with the goal of getting the right result using different expressions of color.
In today’s article, we’ll dive deeper into these concepts, further illuminating the intricacies of color science in the printing world.
LCH: The Triad of Color Science Precision
LCH, an acronym for Lightness, Chroma, and Hue, is an extension of the Lab color space, offering a richer portrayal of color. While Lightness captures a color’s brightness, Chroma assesses its intensity or vividness. Hue, on the other hand, determines the object’s actual color, be it red, blue, green, or anything in between.
Hue and Its Importance
Hue is crucial. It plays a pivotal role in determining an object’s true color. A slight alteration in the hue angle can result in a noticeable difference in the final printed product. For instance, a slight change in the hue of blue can transform it from sky blue to deep ocean blue, significantly impacting the final visual representation, especially in custom label printing.
Hue angle, which is different than (a) or (b) from Lab values, starts at zero degrees or red.
Chroma: Diving Deeper into Color Science Vividness
At its core, Chroma gauges the intensity and purity of a color, effectively determining its vibrancy and the extent to which it captivates the viewer’s eye. High chroma colors are vibrant and impactful, often used to create striking visual effects in printed materials. On the other hand, low chroma colors are muted and can convey sophistication or set a backdrop for more vivid colors. In flexographic printing, understanding Chroma is crucial as it shapes the viewer’s perception of the brand or message.
In essence, while Chroma might seem like a technical color science term reserved for color specialists, its implications are far-reaching. It directly influences the visual appeal, effectiveness, and overall success of printed materials, making it a vital component in the printing process.
Chroma is the distance from the Lightness axis which is zero Chroma at the centre of the sphere.
The lightness value, L, defines black at 0 and white at 100. The lightness value is calculated using the relative luminance of an object represented by the human eye’s response to light. The angle where both C and H = 0 (at the center of the sphere) means achromatic colors or the gray axis.
LCH: How it Works
Consider a color (red):
- the Hue value will describe what type of red, for example, a red fire engine vs a red apple;
- the Chroma value will determine how intense, rich, or saturated the red is;
- the Lightness will indicate how bright from dark to light the red is.
Color Sciense & Spot Ink Formulation
Within the bustling world of the flexo industry, dedicated ink technicians, frequently operating from specialized ink rooms, engage in the meticulous craft of producing spot inks. Their mission? To precisely align the Lab and LCH values simultaneously with a PMS target or previously printed piece.
Consider this intricate process:
- Starting the Blend: A technician begins by blending base inks, for example, using colors like Green and Phthalo Blue.
- Targeting Hue: The primary objective of the initial blend will be to achieve the desired Hue value.
- Refining Hue and Introducing Lightness: Depending on the results of the first blend, subsequent iterations refine the Hue and start aligning the Lightness value.
- Harmonizing with Chroma: As the process advances, attention shifts to the Chroma value, ensuring it is in harmony with the perfected Hue.
- Adjusting Darkness: If the Lightness value still appears too low, Black might be added to adjust the Lightness. As the L, C, and H values are coming closer to the sample target value, the a and b values of Lab color will naturally fall in line in most cases.
- Meeting Delta E Benchmarks: The adjustments continue, with each iteration aiming to bring the ink within the company’s set Delta E standards.
In the photo below, an ink technician is creating an ink sample with measurements in both Lab and LCH that is trying to match all the values of the target standard as closely as possible and within a desired Delta E, in this case, 0.59. Even at this very close match, the ink formulation software is indicating that there is a slight red and blue issue. However, being that close to the standard values is well within acceptable tolerance.
If the ink technician needed to change just the (b) value of Lab, ink formulation would be more difficult to achieve – which is why LCH space is imperative to match color accurately.
Snapshot of Kwality Labels Ink Formulation Result
Lab: The ‘other’ color space
The CIELAB color space, also known as L*a*b* or Lab, is a color space defined by the International Commission on Illumination (CIE) in 1976. A given numeric change in any of the Lab values corresponds to a perceived change in color. This space is very well used throughout the printing industry.
L in Lab and LCH is exactly the same which stands for lightness.
a in Lab
The “a” axis represents greenness (-100 a) to redness (+100 a). One way to help remember this, “a” is for apples which come in red and green varieties.
b in Lab
The “b” axis represents the blueness (-100 b) to yellowness (+100 b). One way to remember this, “b” is for blue and bananas which are yellow.
Lab: How it Works
In the above instance:
PMS 2597 is a purple color. But when describing this in the Lab color space, based on the +35 a* value, we would say this is more red, less green. And based on the -48 b* value, the color is more blue, less yellow. It is the combination of the more red (a) and more blue (b) that makes the purple we see. The lightness of the color is reflected in the L value. In LCH space, the difference is that one would only ever talk of purple – never red, green, yellow, or blue.
Color Science: Angles, Ink, and G7 Compatibility
In the printing world, the hue angles for CMYK inks are pivotal for G7 compatibility, ensuring uniform color reproduction. For magenta ink, the hue angle is typically 357 degrees. Cyan, on the other hand, requires an angle of 233 degrees. Yellow aligns with G7 standards at an angle of 93 degrees, while black, being achromatic, doesn’t have a hue angle but its luminance is critical – Lightness 16. Adherence to these specified angles ensures accurate color representation. By recognizing and using these precise hue angles, printers can achieve consistent color outputs, solidifying the importance of the G7 standard in the industry.
Challenges and Adjustments in CMYK Printing
CMYK printing, while foundational, presents its challenges. A deviation can impact the final print’s quality and accuracy. Recognizing these discrepancies and making informed adjustments is pivotal. For example, a color leaning too green might need a magenta infusion. Such nuances are essential in the flexo industry, where precision is the name of the game.
Color Adjustments for Accuracy
In the realm of printing, the subtleties of colors and shades can be the difference between a good print and a perfect one. A blue that feels too deep might be lightened with a touch of yellow. Then there’s the challenge with purples; they might sometimes lean too close to indigo and could benefit from a dash of magenta. On the other hand, an orange that’s not vibrant enough could be enhanced with a hint of red. It’s all about recognizing these color nuances and making precise tweaks. Such meticulous attention to detail ensures that every shade resonates perfectly in custom label printing, echoing the complexities and solutions inherent in color adjustments.
Tools Used to Measure Lab and LCH Color
Techkon SpectroDens and Xrite Exact are among two of the most popular devices used to measure color values whether in the ink room, during printing on the press, or during quality control to ensure standards are matched as required. Both these devices were outlined in a previous blog post regarding Delta E.
LCH color space dependency was used in the printing industry until the more advanced Lab space was introduced.
Some companies today only rely on Lab color space as it is more technically accurate.
Other companies use neither color space and hence the dependency is totally on the individual performing the task of color matching. This introduces the possibility that today’s color print is not the same tomorrow.
The benefit of using both color spaces for different applications throughout the printing process is that color accuracy is consistent day after day. This is explained above in the ink formulation example.
LCH is an artistic expression of color, whereas, Lab is scientific.
Color space is not a perfect math – it can be quite complex.
Its theory tells one how to get the color required but in the practical world, it may sometimes be a challenge to get the perfect color.
Achieving Color Perfection with Kwality Labels
Color science, with its intricate Lab and LCH values, is central to the flexographic printing industry. At Kwality Labels, we pride ourselves on our commitment to excellence. Harnessing state-of-the-art techniques and profound expertise, we guarantee our clients unmatched perfection in color matching. The world of color science is complex, but with precision, expertise, and a keen eye, stellar color matching is always within reach. Contact Kwality Labels today to bring your color visions to life, ensuring they resonate with perfection and authenticity.