DLI Implementation and Reference Guide - Datalogics

12.6 DLI Implementation and Reference Guide
Values for Color Channels
Concepts and Facilities: Guide to the DL Pager Composition System
The values specified for the color channels vary from space to space, but the most
common values range between zero and 1. Since these values are specified to the
Adobe PDF Library as ASFixed values, this allows 16 bits of precision.
Value Conversion and Inversion
Your own system may specify color internally with a greater or lesser precision, or in
inverted values. These must be converted to the Adobe PDF Library’s view of color to
function correctly.
Generally, you should first correct the precision, matching it to the Adobe PDF
Library’s 16 bit precision, then correct the inversion (if there is one) by subtracting the
number from an ASFixed one.
When the precision difference is a matter of powers of two (as it often is), precision is
corrected by shifting the value to match the Adobe PDF Library’s ASFixed format;
e.g. if you are carrying color as a value of 0-255, shifting left 8 bits will correct
precision.
When the color specification is not in binary, e.g. zero to 100 or zero to 1000, try
converting via floating point numbers. You may also create a subroutine to convert
color values in precision and direction from the source system to the Adobe PDF
Library’s system.