Inside the booth
Use colour-difference numbers only for a controlled print pair
A ΔE score is useful when the samples and viewing conditions match.
A colour-difference number can make a print comparison more repeatable, but the value is not a universal grade for portrait quality. CIE guidance addresses comparable images on the same medium under similar viewing conditions. Change the printer, paper or room light and the comparison may no longer answer the same question.
Define the pair before measuring
Choose one reference strip and one test strip from the same camera source or a controlled colour target. Keep the output medium, print size and lighting consistent. CIE’s image-evaluation report describes instrumental and visual comparison for similar images presented side by side under similar viewing conditions.
Evidence: International Commission on Illumination technical report
Keep a number tied to its method
If you calculate a colour difference, record the formula, sample region, measurement instrument and viewing setup. A CIEDE2000 value uses CIELAB coordinates and is intended to describe colour differences between stimuli under stated conditions; it does not tell whether a skin tone is attractive or whether an entire booth workflow is accurate.
Evidence: International Commission on Illumination technical report
Pair the score with a visual check
Compare the same patch or portrait region side by side, then inspect the whole strip for skin, dark clothing and backdrop changes. If the numeric difference improves while faces look less natural, report both findings. Keep the print samples and capture settings so a later media or light change does not turn the score into a misleading before-and-after claim.
Evidence: International Commission on Illumination technical report
Sources & further reading
Sources for the specific facts and product descriptions above. Our worked examples, interpretations and practical suggestions are original editorial guidance.
- CIE, Methods for Evaluating Colour Differences in Images (CIE 199:2011)International Commission on Illumination technical report