The reason older photocopiers don't copy blue is very simply that the
drum was activated by reflected light from the scanner. The chemical
process that creates the "semiconductor" on the drum surface is
sensitive to a fair proportion of the light spectrum, but frequently
lost sensitivity t the blue portion of the range. Organic
photoconductors had a better response to blues but still cut off a
portion of the spectrum. Newer Photocopiers (Digital) operate
differently and are dependent on the frequency range of the CCD in the
scanner, they are usually pretty good at the blues, and frequently
have settings that enable Text enhancement, enabling a setting of a
contrast point, anything darker than that point is registered as black
anything lighter as white.
"""
The reason older photocopiers don't copy blue is very simply that the drum was activated by reflected light from the scanner. The chemical process that creates the "semiconductor" on the drum surface is sensitive to a fair proportion of the light spectrum, but frequently lost sensitivity t the blue portion of the range. Organic photoconductors had a better response to blues but still cut off a portion of the spectrum. Newer Photocopiers (Digital) operate differently and are dependent on the frequency range of the CCD in the scanner, they are usually pretty good at the blues, and frequently have settings that enable Text enhancement, enabling a setting of a contrast point, anything darker than that point is registered as black anything lighter as white.
"""
http://answers.google.com/answers/threadview/id/536535.html