The TED file format is an ISO standardized file format, allowing tone curves to be exchanged among different prepress systems.
A TED file contains not one but a bundle of curves, each curve linked to a specific ink. So one TED file can contain the adjustment curves of all inks used in a specific printing condition (e.g. four curves to adjust dot gain for C, M, Y, K).
A specific printing condition is the bundle of parameters in a printing process that influences printed outcome. These parameters can be: type of press, type of paper, type of inks, and also the used screen or screening technology (e.g. FM/AM, 150LPI/250LPI, etc.).
The printed outcome of a printing condition is the "color response" of that condition. It is indicated by the color of the Ink solids, the Ink tones scales (dot gain) and overprint behavior (color appearance when printing different inks very close or on top of each other). To print colors as accurately as possible, the color response of a printing condition must be known and kept constant, so that
Colored designs (e.g. RGB tones) can be converted accurately to single-ink separations (e.g. CMYK tones).
Printed colors can be predicted (proofing).
Registering this color response is done by profiling: Printing patches composed out of different inks and ink tones, and saving the measured colors of these patches in a profile. Maintaining this color response is by keeping inks and ink tone scales equal to the scales used during profiling. Because profiling is expensive and time consuming, most printers will calibrate a printing condition towards a standardized condition: All printing parameters are kept as close as possible towards the parameters as defined in the specific standardized condition. This way, pre-press can use a standard profile to separate and predict color outcome.
By keeping the adjustment curves of all inks as one set, dot gain can be controlled more easily towards a specific printing condition or profile, or towards a specific printing standard.