A mobile phone accessory configured to be functionally and structurally associated with a smartphone capable of running a program for executing functions and having a camera and a flash, and to be associated with an area of interest (AOI) target of a material, said mobile phone accessory comprising:
- a support and handling casing having an opaque wall delimiting an internal space of the casing that is adapted not to be disturbed by ambient external light from outside of the casing, the opaque wall having an inner face, an outer face, a rear wall portion comprising a camera window, and a front wall portion comprising an outer radius and a center in which a measuring orifice having a radius is located, the outer radius being at least three times greater than the radius of the measuring orifice, the measuring orifice being configured to be associated with the material of the AOI target, located within a light incident spot;
- colored targets fixed on the casing and located within the internal space and the light incident spot;
- a lighting means having a lighting axis, being arranged at least partly in the casing, and being configured to produce the light illuminating the light incident spot;
- a camera field of view means having a field of view axis, being arranged at least partially in the casing, and being configured to capture a reflection photo of the light incident spot and its content, the field of view axis being perpendicular to a reference plane that is substantially parallel to a substantially flat surface of the material of the AOI target;
- and a scattering plate being located within the casing and being parallel to the reference plane, the scattering plate being configured to be functionally associated with the lighting means, the scattering plate having a scattering opening, a camera field center, and a lighting center, the camera field center being at the intersection of the field of view axis and the scattering plate, which is the center of the scattering opening, and the lighting center being at the intersection of the lighting axis and the scattering plate, wherein the scattering opening is located within the camera field of view means, and through the scattering opening is seen the light incident spot with the measuring orifice, which is configured to be associated with the material of the AOI target, and the colored targets;
- wherein:
- the front wall portion extends facing and spaced from the rear wall portion, parallel between them and to the reference plane;
- the outer face of the front wall portion comprises an area extending in both directions of the reference plane and surrounding the measuring orifice, the outer face being configured to be put into contact with the material located outside, around the AOI target, and to conceal any passage of the ambient exterior light from outside of the casing;
- the inner face and the outer face of the front wall portion extend at least substantially flat for a length in both directions of the reference plane contrary to a simple edge;
- the colored targets are a number N of color measurement targets, each in a shape of a dot and forming together a color measurement area unity, the number N of color measurement targets being a sufficient number to permit an accurate measure of the color of the AOI target and to define colors of the color measurement targets within a narrow gamut of colors representing the whole range of AOI target colors;
- the N color measurement targets are fixed onto the inner face of the front wall portion, placed side by side and adjacent to each other to form at least one line of the color measurement area unity around and proximate to the measuring orifice, the color measurement area unity being annular with a radius greater than the radius of the measuring orifice by less than four times the radius of the measuring orifice, and the color measurement area unity has a center that is also a center of the light incident spot;
- the measuring orifice and the N color measurement targets are part of the light incident spot and included within, the opaque wall having a thickness around the measuring orifice on the rear wall portion that allows a similar distance between the camera window and the AOI target and the N color measurement targets;
- the camera window is configured to allow simultaneous taking of a photo of the AOI target and the N color measurement targets;
- and the mobile phone accessory is configured to be functionally and structurally associated with the smartphone capable of running the program so as to form a device for measuring the color of the AOI target by capturing a photo of the lighted AOI target and the lighted N color measurement targets, with the same illumination conditions, and processing said photo to compare the color of the photographed AOI target with the colors of the photographed color measurement targets of the color measurement area unity.