A multi-angle colorimeter includes an index calculation unit that calculates, based on a predetermined calculation formula, an index corresponding to a particle diameter of a glittering material, which is used for metallic coating or pearl coating, using optical parameters used in color evaluation of the metallic coating or pearl coating on a surface of an object.

A measuring apparatus that measures an optical characteristic of a surface in accordance with a standard selected from a plurality of standards is provided. The apparatus includes an illumination device configured to illuminate the surface with light from a light source, an imaging device configured to image the light source with reflected light from the surface illuminated by the illumination device, and a processor configured to process image data having number of pixels obtained by reducing number of pixels of the imaging device by a reduction rate to obtain the optical characteristic of the surface. The processor is configured to determine the reduction rate based on the selected standard.

A difference between a peak reflectance of a first wavelength component and a reflectance of a second wavelength component having a predetermined wavelength among reflectances of a plurality of wavelength components constituting reflected light in a highlight direction from a glitter material-containing coating film is set as a first difference value. Reflectance is measured of the first and second wavelength components of the reflected light in the highlight direction for the coating film corresponding to a measurement object. A first difference value is calculated by using the measurement result. A storage stores in advance correlation information indicating a correlation between the first difference value and an index value indicating predetermined physical characteristics of a glitter material contained in the coating film. An index value calculator calculates the index value of the coating film corresponding to the measurement object by using the correlation information and the first difference value calculated in the first calculator.

An optical system (230) comprises an image sensor (231), a reference sensor (232), and an optical multiplexer (300). The optical multiplexer defines a first area for receiving a first portion of incoming light and a second area (320) for receiving a second portion of the incoming light. The second area radially surrounds the first area. The optical multiplexer is arranged to direct the first portion of the incoming light to the image sensor (231) and the second portion of the incoming light to the reference sensor (232). The optical multiplexer may take the form of a pinhole minor (300).

Method for acquiring local gonio-reflection characteristics of an image which is aggregation of dots. Sensory glossiness (L) of the image determined by equation (1) is 1.0 or more. The sensory glossiness (L) is determined based on a height of a peak (H), a height of a base (B) and a half width of a peak (W) of a distribution information of lightness with respect to light receiving angle, obtained by measuring reflected light of a measuring light irradiated into the image. The local gonio-reflection characteristics is acquired with a spatial resolution (A) for acquiring the local gonio-reflection characteristics and a resolution (B) which represents a distribution information of the dots within a region where the sensory glossiness (L) being 1.0 or more, satisfying formula (2).
L=Log((H?B)/W)Equation (1)
0.8<A/B<10Formula (2)

A color measuring apparatus includes a measurement assembly which includes at least one illumination assembly for applying substantially parallel illumination light to a measurement spot of a measurement object and a pick-up assembly for capturing the measurement light radiated back from the measurement spot in an observation direction and for converting the same into corresponding electrical signals. The illumination assembly includes at least two illumination subassemblies which illuminate the measurement spot from different illumination sub-directions near a first preset nominal illumination direction, each with preferably parallel illumination light. By the illumination from different illumination sub-directions slightly deviating from the nominal illumination direction, angular errors of the illumination assembly can be compensated for in a simple manner.

A difference between a peak reflectance of a first wavelength component and a reflectance of a second wavelength component having a predetermined wavelength among reflectances of a plurality of wavelength components constituting reflected light in a highlight direction from a glitter material-containing coating film is set as a first difference value. Reflectance is measured of the first and second wavelength components of the reflected light in the highlight direction for the coating film corresponding to a measurement object. A first difference value is calculated by using the measurement result. A storage stores in advance correlation information indicating a correlation between the first difference value and an index value indicating predetermined physical characteristics of a glitter material contained in the coating film. An index value calculator calculates the index value of the coating film corresponding to the measurement object by using the correlation information and the first difference value calculated in the first calculator.

A color measuring apparatus includes a measurement assembly which includes at least one illumination assembly for applying substantially parallel illumination light to a measurement spot of a measurement object and a pick-up assembly for capturing the measurement light radiated back from the measurement spot in an observation direction and for converting the same into corresponding electrical signals. The illumination assembly includes at least two illumination subassemblies which illuminate the measurement spot from different illumination sub-directions near a first preset nominal illumination direction, each with preferably parallel illumination light. By the illumination from different illumination sub-directions slightly deviating from the nominal illumination direction, angular errors of the illumination assembly can be compensated for in a simple manner.

A color measuring apparatus includes a measurement assembly which includes at least one illumination assembly for applying substantially parallel illumination light to a measurement spot of a measurement object and a pick-up assembly for capturing the measurement light radiated back from the measurement spot in an observation direction and for converting the same into corresponding electrical signals. The illumination assembly includes at least two illumination subassemblies which illuminate the measurement spot from different illumination sub-directions near a first preset nominal illumination direction, each with preferably parallel illumination light. By the illumination from different illumination sub-directions slightly deviating from the nominal illumination direction, angular errors of the illumination assembly can be compensated for in a simple manner.

Embodiments of the invention relate to the automatic measuring of such qualities of a printed sheet as reflectance excluding specular reflectance, reflectance including specular reflectance, e.g. gloss, transmittance, half-tone coverage, and the like.