Delta-E is a unit for the colour distance between two colours. The larger the number, the greater the “distance” between the colours. The main idea is that a Delta-E colour distance – in any direction – looks the same to the human eye. So if one colour is brighter by 5 Delta-E than another, to the human eye it looks just as distant from a colour that is redder or bluer by 5 Delta-E.
The most common method is Delta-E76 or CIE 1976 / CIE76.
This method uses the Euclidean distance, between the LAB colour values of the colour.
The calculation formula is: Square root of (L-distance squared) + (a-distance squared) + (b-distance squared)
Example: How far apart are the colours in Delta-E76:
Colour 1: LAB 90/65/55
Colour 2: LAB 87/65/58
square root of [((90-87) = 3 squared) + ((65-65) = 0 squared) + ((55-58) =-3 squared)]
Square root of [(9) + (0) + (9)]
Square root of (18)
So CIE76 is quite easy to calculate, but the Delta-E76 calculation has its drawbacks, as it has been shown that the same Delta-E76 colour distance from the eye is not really seen as equally spaced, so newer calculation methods were established.
Other common methods are…
Delta-E00 is currently the most common method used in proofing and printing technology, Delta-E CMC is widely used in textile printing.
Densitometers measure ink density and optical density.
Incident light densitometers measure prints or photo prints, transmitted light densitometers measure films for printing plates or screen printing, slide films and negative films.
But compared to a colorimeter or a spectrophotometer, a densitometer can only measure tonal values but no colour tones, they are practically colour-blind.
Important for proofing: Densitometers can indeed measure colour densities, but two identical colour densities do not necessarily have the same colour impression. Densitometrically measured values from a proof cannot be compared with the same values on an offset print, a print cannot be adjusted densitometrically to the values of the proof.
Densitometers from Techkon are very common in pressrooms.
A design grid is an auxiliary construction and helps to place the texts, pictures and graphics in the layout. It serves to standardize the document.