d’Optron is continually researching into new technologies as part of our research culture. One such is the use of hue as a means of determining phase difference, birefringence and stress from color photoelastic fringes. Since hue provides color visualization as seen by the human eye, it provides a better means of fringe identification as in Michel-Levy chart. With the advent of digital technologies, this approach can now be digitized. However, digital images represent color as RGB components and usually it is difficult to directly glean any useful information from these values due to different variations. Instead, we proposed using Hue as a means of quantifying colors and hence quantitatively measuring phase difference and birefringence (or stress). Furthermore, since hue ranges from 0 to 360, it appears to be closely linked to the phase which spans the same range. However, as with any color-based approach, hue does not have a quantitative measure which in traditional interferometry is provided by the wavelength.

However, since the hue is wrapped at 2π intervals akin to phase – this interval can be calibrated with the appropriate path difference. This calibration depends on the illumination and recording wavelengths. To enable accurate measurement, an RGB LED with known central wavelengths and a monochrome camera are used to record the images three R, G and B images. Hue was then deduced using standard RGB to Hue algorithm, which provide the Hue in the range of 0-360 or normalized to span the range of 0 to 1 to correspond to fringe order in normal polariscopes.