Acquisition process
The acquisition process was carried out through a system composed of a base with a slot to accommodate the object to be photographed, a dome illuminator and a digital camera (Fig .1). A rotatable support at the top of the dome made it possible to acquire images of the object under different rotation angles. Each tile was placed in the slot and 10 images were taken at different rotation angles from 0° to 90° by steps of 10°.

Acquisition system
Fig. 1 The acquisition system*

The illumination conditions were kept constant throughout the whole acquisition process. The images were captured at the natural resolution of the camera's sensor (2560px × 1920px), and were finally cropped to a  a central part of size 1500px × 1500px corresponding to an area of ≈21cm × 21cm. For colour calibration an X-Rite Digital SG colour checker (140 colour targets) was also put in place and imaged. The RGB values of the 140 colour targets were acquired using the same settings adopted for the tiles; the corresponding device-independent CIE XYZ coordinates (under illuminant D65) were measured through a Minolta CR-200 Chroma Meter (CalibrationData.csv, CalibrationData.pdf).

Technical data

Spectrum Illumination Monster Dome Light 18.25" with white HB LEDs. Technical data aveilable here.

Edmund Optics EO-5012C LE. Technical data available here.

Camera's settings
  • Image resolution: 2560 x 1920
  • image format: BMP
  • Encoding: linear (no gamma correction)
  • Frame rate: 2.40fps
  • Exposure time: maximum allowed by the frame rate
  • Overall gain: 1x
  • Colour gain (determined through white balancing): R = 14x, G = 1x and B = 5x
Illumination settings
  • Voltage: 15V
  • Average illiumination level at the surface of the tiles:  ≈600lx
*IT patent no. 1413266
Università degli Studi di Perugia
Dipartimento Ingegneria Industriale
Via G. Duranti, 67
06125 Perugia (ITALY)
Tel.: 0039 075 5853706
Universidade de Vigo
Escuela de Ingeniería Industrial
Campus Universitario
36310 Vigo (SPAIN)
Tel.: 0034 9868 18602

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