Development of Multi-Spectral Scanner by
Using LEDs Array for Digital Color Proof

Shoji Yamamoto*, Norimichi Tsumura*,
Toshiya Nakaguchi*, and Yoichi Miyake**

* Department of Information and Image Sciences, Chiba University
** Research Center for Frontier Medical Engineering, Chiba University

Journal of Imaging Science and Technology, Vol.51,No.1, pp.61-69, (2007). 

Abstract
We have developed a multi-spectral scanner with LEDs array and photodiode array to measure the reflectance spectra for printing proof accurately. The system is composed of LEDs array with five different spectral radiant distributions and 2048 silicon photodiodes with SLA (Selfoc Lens Array) for imaging to measure printings. Five kinds of LEDs were selected from 40 kinds of LED with different spectral radiant distribution on the market to minimize the average color difference DE*94 between the measured and estimated reflectance spectra of typical 81 color charts. The multiple regression method based on the clustering and polynomial regression algorithm was introduced for high accurate estimation of the spectral reflectance for printing. The result shows that the average and maximum color difference DE*94 between the measured and estimated reflectance spectra of 928 color charts were 1.02 and 2.84, respectively. The scanner can measure the reflectance of print with 0.5mm pitch resolution and 100 mm/s scanning speed. The FPGA (Field Programmable Gate Array) and DSP (Digital Signal Processor) were introduced to accelerate the calculation of sensor calibration and estimation of reflectance spectra of printing proof for practical and commercial use. As the result, the developed scanner could measure the reflectance spectra of printing proof within 20 seconds.

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