How it works:
A colorimeter is an optical instrument based on the principle of photoelectric integration or spectroscopy, which is used to quantify the color of the surface of an object. Its core function is to simulate the human eye's induction of the three primary colors of red, green, and blue, and convert color information into digital chroma values. The most commonly used color space is CIEL*a*b*, where L* represents luminosity, a* represents red-green chroma, and b* represents yellow-blue chroma. The difference between two colors, the chromatic difference ΔE, can be calculated by the following formula:
ΔE = √[(ΔL*)² + (Δa*)² + (Δb*)²]
This formula quantifies the overall difference in color perception. Modern spectrochromatic analyzers can also provide complete spectral reflectance curves, providing a data basis for more accurate color analysis and formulation. The main performance parameters of the instrument include measurement geometry (e.g., d/8° with specular reflection or excluding specular reflection), light source type, observer viewing angle, and instrument-to-table difference, which must be selected to strictly match the surface characteristics and measurement standards of the printed material.
Color management in packaging printing faces multiple challenges. Firstly, there are various printing materials, including paper, plastic, metal, etc., and their surface gloss, texture, and ink absorption vary significantly, which directly affects color presentation. Secondly, the printing process is complex, involving offset printing, gravure printing, flexo printing, digital printing and other methods, and the color reproduction characteristics of each process are different. In addition, there are many supply chain links, from design, proofing to mass production, and it is very easy to produce color deviations between different equipment and different batches. Finally, the subjective evaluation of the human eye is easily affected by ambient light, observation angle and individual differences, and lacks objective consistency. These factors make the establishment of a stable and transmissible objective color quality control system an urgent need in the industry.
Specific applications:
The application of colorimeter runs through the whole process of packaging and printing, and builds a closed-loop management from standard establishment to production control.
Standards establishment and digitization: The standard proofs or digital standard files (e.g. CMYK values) confirmed by the customer are the starting point for color management. The colorimeter is used to measure the standard sample multiple times, and the average value of the standard L*a*b* value and tolerance range are taken to transform the subjective standard into objective and quantifiable data.
proofing and signing: During the proofing stage, the colorimeter is used to quickly compare the ΔE of the color difference between the proofing draft and the standard proof. Through the data, it is judged whether the proofing is within an acceptable tolerance range, providing a scientific basis for signing samples and avoiding directional errors in subsequent production.
Printing process controlDuring mass production, the operator regularly extracts the printed product and uses a colorimeter to measure key color blocks (such as CMYK primary color, spot color, important compound color). Real-time monitoring of the trend of ΔE value can adjust printing parameters such as ink volume and pressure in time when the color deviation exceeds the warning line, so as to achieve preventive control and reduce the scrap rate.
Batch-to-batch consistency assessmentFor long or supplementary orders, colorimeters are a core tool for evaluating color consistency between different production batches. By comparing the data of different batches of products with the original standard, the stability of brand colors in time and space is ensured.
Supplier incoming material inspection: Measure the color of raw materials such as ink and paper to ensure that the incoming material meets the technical specifications and control the color variable from the source.
Key points of implementation
The effective application of colorimeters requires the following key points. Before measurement, the instrument needs to be calibrated and the measurement conditions (such as measurement aperture, light source mode, whether or not it contains mirror light) should be unified. For textured or uneven packaging materials, multi-point measurements should be taken to average the value. Establishing reasonable tolerance standards is crucial, usually based on customer requirements, process level, and human visual tolerance. A common tolerance reference range is as follows:
| Chromatic aberration ΔE range | Visual perception vs. usual acceptance |
| ΔE < 1.0 | The differences are minimal, discernible to professional observers, and generally acceptable. |
| 1.0 ≤ ΔE < 2.0 | There are slight differences, which can be detected on a closer comparison, and most industry standards require this range. |
| 2.0 ≤ ΔE < 3.5 | There are visible differences, and some occasions with less strict color requirements are acceptable. |
| ΔE ≥ 3.5 | There is a noticeable color difference, which is generally unacceptable. |
It should be noted that a single total ΔE value is sometimes not enough to describe the problem, and should be analyzed in combination with ΔL*, Δa*, and Δb* sub-data, for example, ΔL* is negative means the color is dark, and Δa* is positive means reddish, so as to guide the precise adjustment direction.
Conclusion
In the field of packaging and printing, colorimeters transform subjective color perception into objective and traceable digital indicators, serving as a key bridge between design intent and production realization. By systematically integrating it into the color management process, enterprises can significantly improve the efficiency of color communication, reduce production waste, and ensure the consistency of product colors, thereby maintaining and enhancing brand value through stable packaging visual quality in the fierce market competition. The continuous development of technology, such as the application of online color aberration detection systems, is driving the evolution of color management in a more automated and intelligent direction.
References
1. National Printing Standardization Technical Committee. Printing Technology Printed Color Measurement Part 1: Measurement Conditions and Instruments. China Standard Press.
2. ISO 13655:2017. Graphic technology — Spectral measurement and colorimetric computation for graphic arts images.
3. Hunter, R.S., and Harold, R.W. The Measurement of Appearance. John Wiley & Sons.
4. A printing technology journal. Application practice of color management and standardization in packaging and printing. Issue 5, 2022.