7.2 Transmissive Hardcopy Printers

For transmissive hardcopy printing, the relationship between luminance, L, and the printed optical density, D, is:

[pic]

where:

L0 is the luminance of the light box with no film present, and

La is the luminance contribution due to ambient illuminance reflected off the film.

If film is to be printed with a density ranging from Dmin to Dmax, the final luminance will range between:

[pic] , [pic]

and the j values will correspondingly range from jmin = j(Lmin) to jmax = j(Lmax).

If this span of j values is represented by an N-bit P-Value, ranging from 0 for jmin to 2N-1 for jmax, the j values will correspond to P-Values as follows:

[pic]

and the corresponding L values will be L(j(p)).

Finally, converting the L(j(p)) values to densities results in:

[pic].

Note: Typical values for the parameters used in transmissive hardcopy printing areL0 = 2000 cd/m2La = 10 cd/m2.