Accurate representation of interference colours (Michel–Lévy chart): from rendering to image colour correction

Abstract

Here a work flow towards an accurate representation of interference colours (Michel-Lévy chart) digitally captured on a polarised light microscope using dry and oil immersion objectives is presented. The work flow includes accurate rendering of interference colours considering the colour temperature of the light source of the microscope and chromatic adaptation to white points of RGB colour spaces as well as the colour correction of the camera using readily available colour targets. The quality of different colour correction profiles was tested independently on an IT8.7/1 target. The best performing profile was using the XYZ cLUT algorithm and it revealed a ΔE of 1.9 (6.4 no profile) at 5× and 1.1 (8.4 no profile) at 100× magnification, respectively. The overall performance of the workflow was tested by comparing rendered interference colours with colour-corrected images of a quartz wedge captured over a retardation range from 80-2500 nm at 5× magnification. Uncorrected images of the quartz wedge in sRGB colour space revealed a mean ΔE of 12.3, which could be reduced to a mean of 4.9 by applying a camera correction profile based on an IT8.7/1 target and the Matrix only algorithm (ΔE < 1.0 signifies colour differences imperceptible by the human eye). ΔE varied significantly over the retardation range of 80-2500 nm of the quartz wedge, but the reasons for this variation is not well understood and the quality of colour correction might be further improved in future by using custom made colour targets specifically designed for the analysis of high-order interference colours.

Coccolith mass and morphology of different Emiliania huxleyi morphotypes: A critical examination using Canary Islands material

“…Coccolith images were then captured using a Zeiss Axio Imager Z1 light microscope (Zeiss, Oberkochen, Germany) equipped with a Benford plate for circular polarization [59], a 1.6x optovar, neutral density filters, a Plan-Apo 100x, 1.4 NA oil objective, a 0.9 NA universal condenser, and a Canon 60D DSLR camera (Canon Inc., Tokyo, Japan) with a 5194 x 3457 resolution (a pixel resolution of 0.0003 μm -2 ) for light microscope (LM) analysis. Images were captured in RAW and converted to TIFF in sRGB colour space with gamma 2.2 according to [60]. Size calibration was done using a S8 Stage micrometer (02A00404 from PYSER-SGI Ltd., Edenbridge, UK) with steps 10 μm apart along a line with an overall length of 1000 μm ±1 μm.…”

“…The condenser was partly closed to avoid polarization aberrations [62,63]. Grey values were related to an sRGB Michel-Lévy chart from [60] using the ImageJ function [Calibrate. .…”

Microscale Polarization Color Pixels from Liquid Crystal Elastomers

“…[ 23–29 ] As mentioned above, polarization colors originate from the difference between refractive indices and are crucially dependent on the thickness of birefringent materials as indicated in the Michel‐Levy chart. [ 30–33 ] Thus, LCE colors can be controlled by precisely manipulating the thickness of an LCE layer. Currently, LCE layer thickness is usually controlled with spherically or cylindrically shaped particles or flat films with feature sizes of several micrometers to several hundred micrometers.…”

Segmentation, retardation and mass approximation of birefringent particles on a standard light microscope

“…However, the digital rendering of the Michel–Lévy chart by Sørensen (2013) has some limitations and cannot be universally used with a transmitted light microscope. It did, for example, not include the colour temperature of the light source nor the effect of white balance by the camera when rendering the Michel–Lévy chart (see Linge Johnsen et al ., 2018, for details). Furthermore, Bollmann (2014) did not account for the effect of the condenser on accurate colour reproduction.…”