Dermoscopy and skin imaging light sources: a comparison and review of spectral power distribution and color consistency

Abstract

. Significance: Dermoscopes incorporate light, polarizers, and optical magnification into a handheld tool that is commonly used by dermatologists to evaluate skin findings. Diagnostic accuracy is improved when dermoscopes are used, and some major artificial intelligence (AI) projects have been accomplished using dermocopic images. Color rendering consistency and fidelity are crucial for clinical diagnostics, AI, and image processing applications. Aim: With many devices available on the market, our objective was to measure the emission spectra of various dermoscopes, compare them with other light sources, and illustrate variations in reflected colors from images of a reference sample. Approach: A spectrometer measured the spectral power distribution (SPD) produced by four dermoscope models and three alternate light sources, illustrating differences in the emission spectra. Most dermoscopes use light-emitting diodes (LEDs), which are inconsistent when compared with one another. An LED was compared with halogen, xenon-arc, and daylight sources. Images of a micro ColorChecker were acquired from several sources, and three specific colors were selected to compare in CIELAB color space. Color consistency and color fidelity measured by color rendering index (CRI) and TM-30-18 graphical vectors show variation in saturation and chroma fidelity. Results: A marked degree of variation was observed in both the emission and reflected light coming from different dermoscopes and compared with other sources. The same chromophores appeared differently depending on the light source used. Conclusions: A lack of uniform illumination resulted in inconsistent image color and likely impacted metamerism and visibility of skin chromophores in real-world settings. Artificial light in skin examinations, especially LEDs, may present challenges for the visual separation of specific colors. Attention to LEDs SPD may be important, especially as the field increases dependency on machine/computer vision.

Tunable LED illumination for biological tissue imaging

“…The spectral power distribution (SPD) of the light emitted by TBLEDI is crucial for achieving high color contrast in tissue imaging [10]. Thanks to the high resolution of the images and the ability to adapt the SPD of the light to the specificity of the examined tissue, even subtle abnormalities can be detected [8,11,12]. Green [13], red, and near-infrared [14] lights are used in vascular imaging, as well as red light for pigmentation [15], which can help to extract details from tissue.…”