Closed Loop
Closed loop is a system that stores spectral colour data in a database at the printing press.
The original, or reference colour, is sampled by a spectrophotometer and saved in what is known as the “CieLAB” colour space. The CieLAB colour space is a way of assigning numeric values to different components of the colour. These numeric values are stored in the presses’ database reference not only for the current printing job, but also for subsequent jobs that use the same ink/paper combination. It is called closed loop because the spectrophotometer and the press communicate with each other to control the colour during a press run. The system verifies that the colour being printed on the press sheet matches the colour stored in the database. If it does not, the system makes minor adjustments and corrects the problem.
A typical closed loop system is set to a colour variation tolerance that is imperceptible to the human eye. What this means is that the spectrophotometer can see variances in any colour that the press operator cannot see.
