Relative versus absolute colorimetric, in press language
Absolute comparison includes paper white. If the papers differ, every colour carries that paper gap. Relative comparison lines up paper white first, then asks how far the ink is. Customer wants the whole sheet, paper included, to match: use absolute. Customer wants the ink to match and the paper already changed: use relative, and report paper white on its own.
Absolute comparison includes paper white. If the papers differ, every colour carries that paper gap. Relative comparison lines up paper white first, then asks how far the ink is. Customer wants the whole sheet, paper included, to match: use absolute. Customer wants the ink to match and the paper already changed: use relative, and report paper white on its own.
How the press understands it
Lay the OK-sheet paper next to today’s paper. Absolute tells you: including this paper’s yellow, the ink has to look like the OK sheet too. If the paper went yellow and you cool the ink, absolute colour difference may shrink while the ink itself should not have been moved that way. Relative tells you: admit the papers differ, then ask how far the ink would still be if the papers were the same. That paper gap is reported separately; it is not hidden.
Both are a switch in the instrument. Read colour difference without looking at the switch, and two people will argue two numbers both “already measured.”
The switch
| Customer’s words | Use | Paper white |
|---|---|---|
| Paper included has to match | Absolute | If paper white fails, treat the paper |
| Paper may differ; ink must match | Relative | Paper white on its own line |
| Not said | Ask first | Do not pick absolute and drive the ink the wrong way |
When you record, write
- Absolute or relative next to the colour difference.
- On relative, still attach the absolute colour difference of paper white.
- After you flip the switch, recompute. Do not claim the old number still counts.
