Spectrophotometric measurement estimation

A non-transitory machine-readable storage medium encoded with instructions executable by a processor, the machine-readable storage medium comprising:

• instructions to determine, from received data representative of a first combined spectrophotometric response of a substrate and deposited colorant under a first illumination condition, and from a contribution term indicative of an effect of ultra-violet, UV, light on a combined reflectance of the substrate and deposited colorant, an estimate for a second combined spectrophotometric response of the substrate and deposited colorant under a second illumination condition;
• wherein the first combined spectrophotometric response is indicative of a combined reflectance of the substrate and deposited colorant under the first illumination condition;
• wherein the second combined spectrophotometric response is indicative of a combined reflectance of the substrate and deposited colorant under the second illumination condition;
• and
• wherein the first illumination condition or the second illumination condition is a UV-cut illumination condition.

An apparatus comprising:

• a spectrophotometer to receive light reflected from a printed face of a substrate and to produce an output signal representative of the spectral reflectance of the printed face of the substrate under a first illumination condition;
• a memory;
• and
• a controller to receive the output signal and to process instructions stored in the memory to determine, from the combined spectral reflectance of the substrate and deposited colorant, and from a contribution term stored in the memory, an estimate for the spectral reflectance of the printed face of the substrate under a second illumination condition;
• wherein the contribution term is indicative of an effect of ultra-violet, UV, light on a reflectance of a printed liquid on a substrate;
• and
• wherein the first illumination condition or the second illumination condition is an illumination condition in which UV light is substantially absent.