<p>Color measurement is essential in fields such as textiles, food processing, medical diagnostics, and cultural heritage preservation. Existing techniques—photometric integration, imaging-based methods, and spectrophotometry—face trade-offs between accuracy, spectral completeness, and suitability for non-contact measurement. To overcome these limitations, we propose a high-accuracy non-contact color measurement method based on intensity-modulated illumination spectrum (IMIS). The system applies sinusoidal intensity modulation to a broadband illuminator and continuously records multi-cycle reflected spectra using a spectrometer. A single-beam configuration with a standard white reference replaces direct source measurement. Fast Fourier Transform extracts the modulation component at each wavelength, reconstructing the reflection spectrum while suppressing ambient light interference. Experiments with an X-Rite ColorChecker show that, under darkroom conditions in DC mode, the system achieved average color differences of 0.82 <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(\Delta {\text{E}}_{\text{ab}}^{}\)</EquationSource> </InlineEquation> and 0.61 <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\Delta {E}_{00}^{}\)</EquationSource> </InlineEquation>, with a mean spectral reflectance error of 0.5%, closely matching a commercial spectrophotometer (0.78 <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\Delta {\text{E}}_{\text{ab}}^{}\)</EquationSource> </InlineEquation>, 0.49 <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\(\Delta {E}_{00}^{}\)</EquationSource> </InlineEquation>, and 1.3% error). In modulation mode, results remained stable (0.25 <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(\Delta {\text{E}}_{\text{ab}}^{}\)</EquationSource> </InlineEquation>, 0.18 <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\(\Delta {E}_{00}^{}\)</EquationSource> </InlineEquation>, RMSE = 0.0047, GFC = 0.9996). Under varying ambient light, fluctuations were 0.09 <InlineEquation ID="IEq7"> <EquationSource Format="TEX">\(\Delta {\text{E}}_{\text{ab}}^{}\)</EquationSource> </InlineEquation> and 0.08 <InlineEquation ID="IEq8"> <EquationSource Format="TEX">\(\Delta {E}_{00}^{}\)</EquationSource> </InlineEquation>, with negligible RMSE change (0.0007). Distances of 4–8 cm maintained 0.25 <InlineEquation ID="IEq9"> <EquationSource Format="TEX">\(\Delta {\text{E}}_{\text{ab}}^{}\)</EquationSource> </InlineEquation> and 0.18 <InlineEquation ID="IEq10"> <EquationSource Format="TEX">\(\Delta {E}_{00}^{}\)</EquationSource> </InlineEquation>, while modulation frequencies from 0.1 to 5 Hz produced average variations of 0.09 <InlineEquation ID="IEq11"> <EquationSource Format="TEX">\(\Delta {\text{E}}_{\text{ab}}^{}\)</EquationSource> </InlineEquation> and 0.07 <InlineEquation ID="IEq12"> <EquationSource Format="TEX">\(\Delta {E}_{00}^{}\)</EquationSource> </InlineEquation>, with RMSE < 0.0075 and GFC > 0.9975. These results demonstrate that IMIS enables real-time, high-precision, non-contact color measurement in complex environments, offering strong potential for industrial and scientific applications.</p>

A high-accuracy non-contact color measurement method based on intensity-modulation

期刊论文
发表日期：

2026年1月10日

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Lang Xiao,
Qingwen Fan,
Hongliang Pei,
Qidi Zhang,
Mingtao Zhang

摘要

Color measurement is essential in fields such as textiles, food processing, medical diagnostics, and cultural heritage preservation. Existing techniques—photometric integration, imaging-based methods, and spectrophotometry—face trade-offs between accuracy, spectral completeness, and suitability for non-contact measurement. To overcome these limitations, we propose a high-accuracy non-contact color measurement method based on intensity-modulated illumination spectrum (IMIS). The system applies sinusoidal intensity modulation to a broadband illuminator and continuously records multi-cycle reflected spectra using a spectrometer. A single-beam configuration with a standard white reference replaces direct source measurement. Fast Fourier Transform extracts the modulation component at each wavelength, reconstructing the reflection spectrum while suppressing ambient light interference. Experiments with an X-Rite ColorChecker show that, under darkroom conditions in DC mode, the system achieved average color differences of 0.82 \(\Delta {\text{E}}_{\text{ab}}^{*}\) and 0.61 \(\Delta {E}_{00}^{*}\) , with a mean spectral reflectance error of 0.5%, closely matching a commercial spectrophotometer (0.78 \(\Delta {\text{E}}_{\text{ab}}^{*}\) , 0.49 \(\Delta {E}_{00}^{*}\) , and 1.3% error). In modulation mode, results remained stable (0.25 \(\Delta {\text{E}}_{\text{ab}}^{*}\) , 0.18 \(\Delta {E}_{00}^{*}\) , RMSE = 0.0047, GFC = 0.9996). Under varying ambient light, fluctuations were 0.09 \(\Delta {\text{E}}_{\text{ab}}^{*}\) and 0.08 \(\Delta {E}_{00}^{*}\) , with negligible RMSE change (0.0007). Distances of 4–8 cm maintained 0.25 \(\Delta {\text{E}}_{\text{ab}}^{*}\) and 0.18 \(\Delta {E}_{00}^{*}\) , while modulation frequencies from 0.1 to 5 Hz produced average variations of 0.09 \(\Delta {\text{E}}_{\text{ab}}^{*}\) and 0.07 \(\Delta {E}_{00}^{*}\) , with RMSE < 0.0075 and GFC > 0.9975. These results demonstrate that IMIS enables real-time, high-precision, non-contact color measurement in complex environments, offering strong potential for industrial and scientific applications.