Optimized flash light-emitting diode spectra for mobile phone cameras

Abstract

Flash light-emitting diodes (LEDs) of modern mobile phones lack red and cyan spectral parts, however, the color gamut of their respective displays has increased in recent years. The influence of this discrepancy on the color reproduction of smart phones is investigated in this paper. Based on the CIECAM02 color appearance model, a metric is introduced to judge color reproduction of mobile phones under flash LED illumination. An evaluation method is established to compare the visual appearance of a scene under various surrounding illuminations with the reproduction of that scene. To facilitate a comparison with measurements, the evaluation method is based on the raw data of two test cameras and a Digital ColorChecker SG. To reduce the color shift between perception and reproduction, optimized flash LED spectra are presented. A single-LED and a double-LED concept with adjustable color temperature are derived from these results. Additionally, the common characteristics of flash LED spectra giving good results is investigated, identifying the spectral parts with the most influence on camera color reproduction and showing the spectral parts not contributing or even resulting in poor color reproduction. Finally the efficiency of optimized flash LED spectra is compared to standard flash LEDs.