Cross-polarised and parallel-polarised light: Viewing and photography for examination and documentation of biological materials in medicine and forensics

Abstract

Cross-polarisation, with regard to visible light, is a process wherein two polarisers with perpendicular orientation to one another are used on the incident and reflected lights. Under cross-polarised light birefringent structures which are otherwise invisible become apparent. Cross-polarised light eliminates glare and specular highlights, allowing for an unobstructed view of subsurface pathology. Parallel-polarisation occurs when the polarisers are rotated to the same orientation. When cross- or parallel-polarisation is applied to photography, images can be generated which aid in visualisation of surface and subsurface elements. Improved access to equipment and education has the potential to benefit practitioners, researchers, investigators and patients.

Clinical photography in skin of colour: tips and best practices

“…Clinical photography of light skin often relies on a standard royal blue background; however, white or light backgrounds can also be useful for photographing dark skin because of the contrast and additional light reflection onto the subject (item 2). Use separate light for hair . When taking photos of a patient of colour who has dark hair, a separate light, such as an overhead exam light, can be helpful to highlight detail that otherwise would be missed (Figure 1d), like at the hairline. Parallel light polarization can enhance the appearance of epidermal processes, and may be particularly useful for a subset of images designed for publication or teaching 5 . For lesions that primarily have erythema or pigmentary changes, using cross‐polarization can aid in decreasing light reflectance and glare, which can be particularly useful in darker skin types 5,6 .…”

“…5 For lesions that primarily have erythema or pigmentary changes, using cross-polarization can aid in decreasing light reflectance and glare, which can be particularly useful in darker skin types. 5,6 This can be accomplished in an inexpensive way using a plastic linear polarizer sheet taped over the camera lens and flash of a camera phone. 6 Dermatologists must understand ways to achieve the best photographic representation of all patients in order to optimize patient care and the development of educational photos.…”

Assessing skin tone heterogeneity under various light sources

“…A Canon EOS 6D Mark II camera was used to capture the facial images under each of the different light sources. Additionally, in order to obtain uniform light and reduce the effect of highlights in the images [4], a linear polarizer was placed in front of each LED Cube with a further polarizer placed over the lens of the camera. The positions of two LED Cubes were aligned such that they directly illuminated each face as in Figure 2.…”

“…Different skin coloration in facial areas can be used to judge the physical status of a person as healthy or unhealthy, particularly in the periorbital, cheek, and forehead areas [3]. In clinical utilization, skin color information from images can be a useful tool for diagnostics and surveillance when cross-or parallelpolarization is applied to photography [4]. In the mobile phone industry, different filters are introduced in the cameras to enhance facial skin color reproduction, especially for portraits.…”

An assessment method for dermal structures using cross‐polarized light imaging with a green light‐emitting diode

“…ble. The polarized photographic technique was suggested as a usefultool in the practice of dermatology 6. There are two types of polarized photographic techniques: parallel-polarized light (PPL) and CPL photography.…”