Electronic graphic arts scanners are analogous to the photographic separation methods they replace in that they measure the density of colorants in the red, green, and blue parts of the visible spectrum. Color correction setups to specify conversion to print data are traditionally created by skilled operators using trial and error. With increasing demand for device independent color processing, conversion of scanner densities to colorimetric quantities is needed. We describe a method for scanned transparencies that uses only the spectral characterization of the scanner channels and of the colorants being scanned; the scanner itself need not be modified. The basic idea is simple. First, convert scanner densities to colorant amounts. Scaling the characteristic spectral density curves by these amounts and summing gives reconstruction of the full color spectrum of the pixel. Any colorimetric quantity can then be calculated. The key aspect of the method, calculating colorant amounts, is accomplished with an iterative loop where estimated amounts are processed with the colorant and scanner characterizations to stimulate scanner densities. The errors between these and the actual scanner densities provide corrections to improve the estimates. The iteration converges quickly to the true colorant amounts. This technique is accurate and works well with lookup table methods with negligible loss of accuracy.

Date Published: 8 September 1993
PDF: 6 pages
Proc. SPIE 1913, Human Vision, Visual Processing, and Digital Display IV, (8 September 1993); doi: 10.1117/12.152715

Published in SPIE Proceedings Vol. 1913:
Human Vision, Visual Processing, and Digital Display IV
Jan P. Allebach; Bernice E. Rogowitz, Editor(s)