CALCULATION OF LAYER THICKNESS

1 . Processing circuitry comprising:

circuitry to receive data, the data indicative of a measurement of a region of a substrate, the region having a first layer, and a second layer, the first and second layers provided one above the other with respect to the substrate, the measurement indicative of an optical parameter associated with the first layer;

circuitry to calculate a thickness of the second layer based on the received data.

2 . The processor of claim 1 , wherein the circuitry to receive data is further to receive data indicative of a reference measurement indicative of an optical parameter of the first layer in the absence of the second layer.

3 . The processor of claim 2 , wherein the circuitry to calculate is arranged to determine a difference (≢) between the optical parameter associated with the first layer and the optical parameter of the first layer in the absence of the second layer, and the calculation of the thickness of the second layer is based on Δ.

4 . The processor of claim 3 , wherein the calculation of the thickness of the second layer is based on a comparison between the determined Δ and a predetermined relationship.

5 . The processor of claim 1 , wherein the second layer is transparent.

6 . A printer comprising the processing circuitry of claim 1 , wherein the measurement and calculation are made in-line with the printer.

7 . An imaging system comprising:

A measurement device including a light source and a sensor, the sensor arranged to perform a measurement based on detection of light from the light source that has been reflected from a measurement region of a substrate, the measurement region having a first layer and a second layer one above the other with respect to the substrate; and

processing circuitry to calculate a thickness of the second layer based on the measurement, wherein

the measurement is indicative of an optical parameter associated with the first layer.

8 . The system of claim 7 , wherein the measurement device is further arranged to perform a reference measurement of a reference region, the reference measurement representative of the optical parameter of the first layer independent of the second layer, and

the processing circuitry is to calculate the thickness of the second layer based on both of the measurement of measurement region and the measurement of the reference region.

9 . The method of claim 8 , wherein the optical parameter is selected from a list consisting of: optical density, spectrum, a colour difference or distance, dE, dot area and gloss..

10 . The method of claim 7 , wherein the second layer is transparent.

11 . A method comprising:

determining a change in an optical parameter of a first layer due to a second layer applied over or below the first layer with respect to the substrate;

calculating the thickness of the second layer based on the change in the parameter.

12 . The method of claim 11 , wherein the optical parameter is selected from a list consisting of: optical density, spectrum, a colour difference or distance, dE, dot area and gloss.

13 . The method of claim 11 , wherein the thickness of the second layer is calculated using a predetermined relationship.

14 . The method of claim 13 , wherein the relationship is a substrate dependent calibration.

15 . The method of claim 11 , wherein the second layer is transparent.