In this second work on the Holy Face of Manoppello, known also as the Veil, we have performed a spectral analysis of the transmitted image. Its thin linen threads are translucent, presumably because starched, allowing light to pass through them. As a result, the yellowish colour of the ancient linen and starch contribute substantially to the final hues of the Holy Face, especially when the Veil is lit from the backside with grazing light. Spectrophotometry measurements have allowed calculating how the fabric absorbs the various chromatic components. Through these quantitative evaluations, it has been possible to compensate the colours of the transmitted Holy Face image, by subtracting the contribution due to the yellowish coloration of the thin linen threads. Furthermore, the rotational spectrum of the image has been studied after digital restoration. The linear fit of the power spectrum in bi-logarithmic scale with a power law
provided a slope parameter
. This is a surprising value because it is typical of photographs of human faces, not of portraits of human faces painted by artists, which instead have statistical properties of fractal type, with values of slopes
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