Patent ID: 7296518

Claim:
A method of measuring printed ink concentration on an opaque substrate on-line comprising: (a) projecting a light over the ink printed on the substrate measuring light reflectance as a camera response R, G or B, wherein R is the camera response for a red sensor, G is the camera response for a green sensor and B is the camera response for a Blue sensor; (b) Substituting the camera response R, G or B for reflectance (ρ o ) of the printed ink over the opaque substrate in order to calculate the extinction (E) of light by the printed ink as indicated in the following formula E = ⁢ - 2 b · ln ⁢ { - ( 1 - B 0 ) · ( 1 - ρ 0 ) 2 · ρ · B 0 + [ ( 1 - β 0 ) · ( 1 - ρ 0 ) 2 · ρ · B 0 ] 2 + 1 B - B 0 } wherein B, b and B 0 are constants having values of about 1.0, 4.271 and 0.606, respectively; and (c) calculating printed ink concentration (c) based on the following formula: E=ε×c×t wherein (E) is as calculated in step (b), (ε) is the relative (relative to the scattering of the substrate) unit extinction coefficient, a predetermined measurement of the pre-printed ink per unit concentration per unit thickness and (t) is the thickness of the printed ink either predetermined prior to or measured after printing.