See Nature of the color filter => density status / polarization filter.
The density value is a dimension for the absorption of light by a color. The density value is determined with a densitometer or a spectrophotometer.
When determined with a spectrophotometer: The density value is calculated from the spectrum using numeric filter curves.
The actual dot percentage is computed from the density value.
See also Basics of Physics in Determining Density Values .
•Geometric or physical dot percentage:
This dot percentage results from the purely geometric screen dot size in the screen cell. Only the process-related dot gain that solely affects the geometric dot size is taken into account.
The optical dot gain is not included in this case.
•Actual dot percentage:
This value results from the process-related dot gain and from the optical dot gain.
The actual dot percentage reflects the output tonal value on the printing material that can actually be perceived by the human eye.
Measurement: The density value is determined with a densitometer. The actual dot percentage is computed from the density value.
x axis = nominal values
y axis = measured values
Data curveCreation of a calibration curve (process calibration)
"Measured value" ("Measured%")
This can also be referred to as the actual output tonal value or actual (densitometric) dot percentage.
•Process calibration: The tonal value that is actually produced is measured after printing. The value is measured on the printing material using a densitometer.
The densitometer measures how much light a color absorbs in a certain wavelength range. The density value is the dimension for absorption. The density value is converted to a dot percentage. The actual dot percentage is the output tonal value that is measured and can be perceived approximately by the human eye.
•Linearization: After output to plate or film, the value is measured on the plate with a dotmeter or on the film with a transparency densitometer.
The difference between the nominal and measured value arises through the process-related and the optical dot gain (see above).
This can also be referred to as the input tonal value.
The job data include details about the tonal values on which screening will be based. The size of a screen dot as an input value is a purely geometric dimension. This means that a nominal value of 50% is a tonal value of 50% where 50% of a screen cell is covered, i.e. printed.
The nominal value is the x axis value in the process and data curve (Creation of a calibration curve (process calibration) ).
Process curve / Process curve set
x axis = nominal values
y axis = process values
Process curve Creation of a calibration curve (process calibration)
A process curve set provides the process curves for a certain color set.
You will find the process curve sets as a resource in "Administration > Process Curve Sets" (for more details, see "Administration > Process Curve Sets").
This can also be referred to as the output or target tonal value desired.
A dot gain compared to the input tonal value or nominal value is something which is expected. An ideal value or target value is defined for this dot gain. The process value states how great the output tonal value ideally should be.
In printing, the process value and and the measured value generally deviate. Calibration is used to modify the input tonal values before screening so that the process values will actually be achieved. See also the Principle of Calibration Based on Process Calibration .
The term "tonal value" is used in many different ways. As a nominal value, the tonal value is an input dimension that reproduces the purely physical size of the screen dot. As a measured value or process value, the tonal value is an output dimension for the actual dot percentage.