A method of mapping the crystallinity degree of a polymer coating of a moving metallic substrate, the process comprising the following steps: a) lighting a transversal area of said of said polymer coating encompassing its full width W, with a polychromatic light including wavelengths in the infrared domain, b) measuring with at least one hyperspectral camera, - the light intensity S impacted,λα at a predetermined wavelength λα impacted by the degree of crystallinity of said coating in the infrared domain and - the light intensity S stable,λβ at a predetermined wavelength λβ not impacted by the degree of crystallinity of said coating in the infrared domain of at least two light beams (B1, B2) from said polychromatic light after reflection on said moving metallic substrate on two different locations (L1, L2) within said transversal area, c) determining at least an impacted absorbance A imp, using said light intensity S impacted,λα at said predetermined wavelength λα impacted by the degree of crystallinity for each beam (B1, B2), d) determining at least a stable absorbance A sta, using said light intensity S stable,λβ at said predetermined wavelength λβ not impacted by the degree of crystallinity for each beam (B1, B2), e) determining, for each beam (B1, B2), a ratio, R, equals to A imp /A sta f) converting each ratio R to a degree of crystallinity, g) mapping the degree of crystallinity of said polymer coating in said transversal area using said degree of crystallinity and said locations (L1, L2). a) lighting a transversal area of said of said polymer coating encompassing its full width W, with a polychromatic light including wavelengths in the infrared domain, b) measuring with at least one hyperspectral camera, - the light intensity S impacted,λα at a predetermined wavelength λα impacted by the degree of crystallinity of said coating in the infrared domain and - the light intensity S stable,λβ at a predetermined wavelength λβ not impacted by the degree of crystallinity of said coating in the infrared domain of at least two light beams (B1, B2) from said polychromatic light after reflection on said moving metallic substrate on two different locations (L1, L2) within said transversal area, - the light intensity S impacted,λα at a predetermined wavelength λα impacted by the degree of crystallinity of said coating in the infrared domain and - the light intensity S stable,λβ at a predetermined wavelength λβ not impacted by the degree of crystallinity of said coating in the infrared domain of at least two light beams (B1, B2) from said polychromatic light after reflection on said moving metallic substrate on two different locations (L1, L2) within said transversal area, c) determining at least an impacted absorbance A imp, using said light intensity S impacted,λα at said predetermined wavelength λα impacted by the degree of crystallinity for each beam (B1, B2), d) determining at least a stable absorbance A sta, using said light intensity S stable,λβ at said predetermined wavelength λβ not impacted by the degree of crystallinity for each beam (B1, B2), e) determining, for each beam (B1, B2), a ratio, R, equals to A imp /A sta f) converting each ratio R to a degree of crystallinity, g) mapping the degree of crystallinity of said polymer coating in said transversal area using said degree of crystallinity and said locations (L1, L2).