Method and apparatus for determining a reflectance of a target object

A method for determining a reflectance, of at least a portion of a target object, in at least one selected wavelength range of electromagnetic (EM) radiation, comprising, for each selected wavelength range:

• providing a digital image including at least one target object and a plurality of reference objects, each reference object having respective non-identical predetermined reflectance characteristics, with a digital camera arrangement that provides output image data that comprises digital numbers that are responsive to radiation, in only a selected wavelength range, incident at a sensing plane of the digital camera arrangement, wherein the digital image is a digital representation of a scene including the at least one target object and the plurality of reference objects and wherein the output image data comprises gamma encoded data;
• determining a pre-transformation relationship between a first set of the digital numbers and a first set of the respective predetermined reflectance characteristics of the reference objects, wherein the first set of digital numbers coincide with the digital numbers corresponding to the reference objects and wherein the pre-transformation relationship is non-linear;
• determining a post-transformation relationship between the first set of the digital numbers and the first set of the respective predetermined reflectance characteristics of the reference objects, wherein the post-transformation relationship is linear;
• extrapolating the post-transformation relationship to a further set of digital numbers that coincide with the digital numbers corresponding to a remainder of the scene excluding the reference objects;
• responsive to extrapolation of the post-transformation relationship, transforming a further set of digital numbers to allocate a value of reflectance for each of the digital numbers in the further set;
• for at least a portion of the target object, determining a corresponding first group of allocated values of reflectance;
• and
• responsive to the first group of allocated values, determining a reflectance of the portion of the target object.