Technical Information

Technical Information

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Discussion on Control Methods for Spot Color Dot Enlargement in Packaging and Printing


Release Time: 2026-01-04 00:00:00.000

With the widespread adoption of spot-color halftone images in packaging and printing, accurately reproducing the image gradations and details that meet customer requirements has become crucial. This article starts with two core approaches—control of dot gain and color difference control—and analyzes their technical principles, application scenarios, and optimization directions.

 

Network Expansion Rate Control

By controlling the degree to which the halftone dot area is increased in spot-color printing, ensure that the tonal range of the printed material meets the standards. Common methods include:

1. Mary Davis Formula

This is a traditional method for calculating dot gain. It is commonly used in conventional four-color printing, where the change in dot area is measured to assess tone matching. Some printing plants also routinely adopt this method when controlling the tones of spot colors.

2. SCTV Method

Spot Color Tone Value, the latest spot-color tonal technology based on spectral curves, enables more precise matching of visual hierarchy.

 

Advantage

The dot-area data for SCTV is smaller, the tonal gradations are nearly equidistant, the transition in the shadow tones is smoother, and the 50% tone is closer to the midpoint between the paper color and the solid ink color.

 

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Application

 

Quick setup and measurement using the eXact instrument, combined with dot gain data to digitally represent print tonal ranges.

 

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Color Difference Control (Undertone 50% Color Difference)

 

The color difference between the 50% halftone of the spot color and the printed sample must be evaluated comprehensively by combining the following four methods:

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Key points

When establishing color standards, it is necessary to include tone area values ranging from 25% to 75% (with at least 50%), in order to support multi-method data matching.

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A single method has limitations; it is recommended to combine dot gain control with color difference control to improve midtone accuracy.

 

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Same-tone contrast

 

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Best Match Comparison

 

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Comparison of identical densities

 

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Same Brightness Comparison

 

Summary

In packaging printing, controlling midtones in spot colors requires balancing dot gain and color difference analysis.

1. Network Expansion Rate Control (Such as the SCTV method) can optimize tonal gradation and is particularly well-suited for visually matching dark tones and midtones.

2. Color difference control By conducting multi-dimensional comparisons (such as ΔE, density, and brightness), we can specifically address issues like ink formulations and ink film thickness.

3, Comprehensive Application These two methods, combined with the establishment of standard data that includes multi-level tonal values, are key to achieving accurate color reproduction.

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