Color Prediction for Electrophotographic Prints on Common Office Paper

S. Mourad

Ph.D. dissertation, under the supervision of Prof. R.D. Hersch, Thesis No 2708, presented at the Computer Science Department, Ecole Polytechnique Fédérale de Lausanne, 2003

Digital color desktop printers are widely used in modern offices. However, the ability of the printers to reproduce input colors faithfully is limited and they need to be recalibrated frequently. This is a time-consuming and cumbersome process, which usually needs to be carried out manually.

In order to simulate the interaction of light and color prints and to facilitate the calibration process, this thesis proposes new models for digital color printers and more specifically for dry toner electrophotographic printers. The proposed mathematical models describe the main contributing physical phenomena and offer support for the closed loop control of color halftone printers.

A first model concerns the phenomenon of light scattering within paper and takes into account the fluorescence of brightened office papers. Given the spectral point transmittance of a halftone patch, the model estimates the spectral point reflectance. It is verified by spectral microscopic measurements and is able to estimate the optical dot gain in halftone prints and its effect on the color reproduction curve of common printed papers.

A second model simulates the behavior of the electrophotographic printing process. Starting from the input bitmap of a color halftone, the simulation model computes the microstructures of the toner deposition on a given printing substrate. Assuming non light scattering toners, the obtained toner relief is transformed into the spectral point transmittance required by the first model.

For an electrophotographic printer, both models together allow an accurate estimate of the spectral color response and its description as a function of given input halftoned color separation layers.

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