You can open this view by clicking the "Tonal values" tab.
Display of the dot gain/printing characteristic
The density-based results can be seen in different charts:
•Dot gain
•Printing Characteristic
•Density curve
•CTV (for more details, see CTV in Measure - Functions)
The comparison of the curves in these diagrams makes it easy for you to check the quality of a device or process calibration or linearization.
For linearization (e.g. of an imagesetter or platesetter), a test strip is output and measured, giving you the actual values. The nominal values are specified by device and process standards. Correction values (calibration values) are determined from the nominal and actual values. Ideally, the actual values match the nominal values if you output and measure a test strip again after linearization.
After calibration, you can display the nominal values as reference data and the actual values as comparison data. This allows you to check the quality of linearization and to determine whether and how much the actual values deviate from the nominal values; in other words, whether you have to rerun calibration. This also allows you to detect when a renewed calibration/linearization is necessary. However, this is easier with a long-term analysis (see Working With the 'Analysis' Main Function).
Display
The reference data have curves with continuous lines and the comparison data curves with dashed lines. You can display the curves together or separately for the reference and comparison data and likewise for all colors together or each color separately. You can also display the differential curves.
The following data are used for the comparison:
•the absolute density values measured
•the difference of the measured density values
•the absolute screen percents and dot gains calculated from the density
•a difference of the determined screen percents (identical to the difference of dot gain)
Note: Only screen percents and dot gain are used for plate measurements.
Only the primary colors are evaluated when examining the density. The reason for this is that a unique density value (red, green or blue density filter) that can be used as a reference cannot be assigned for secondary and tertiary colors.
An analysis of this view will give you usable results only if the dot gain curves can be calculated from measured densities and/or spectral values.
For that reason, you should always enable the two respective options in "Preferences > Measurement":
•"Measure and save density values as well (if supported by instrument)"
•"Measure and save spectral remissions as well (if supported by instrument)"
Display of the dot gain curves
Dot gain is the enlargement of screen dots by the printing process. An image can thus appear darker and/or a color shift may occur.
Normally, dot gain is measured in the midtones at 40% and in the shadows at 80%.
Dot gain is the difference between the tonal values before and after processing. It can also be negative (dot loss).
In the diagram with the dot gain curves, the horizontal axis displays the tonal values of the film or data set, and the vertical axis the dot gain.
The dot gain curves or printing characteristics are calculated on the basis of real density values if you also measure the density when measuring the colors (selected in the "Preferences" dialog).
If you don't, the density values are calculated from the spectral values or, if the latter were also not measured, by general approximation from the Lab(xyz) color values.
Display of the printing characteristic
Printing characteristic is used to illustrate in screen percent the relation of the dot areas in print to those on the film or in the data set. The ideal printing characteristic is linear and rises at an angle of 45°.
The printing characteristic depends on the ink used, the properties of the paper, the print form and the way the press works.
The printing characteristics that are determined only apply to the process conditions at hand. If the same data are to be produced on a different press or on different printing stock, the printing characteristics will also change.
In process calibration, you attempt to calibrate the current printing characteristic to a reproducible standard. The calibration curve corresponds to the difference between the printing characteristic you want and the current one of the printing process. Generally, at least four printing characteristics (CMYK process colors) must be set.
Display of the density curves (density profile)
The density profile view shows the density curves scaled from D = 0.0 to D = 3.0, the range that is important for reproduction. The relation between tonal values and density values is shown in this diagram.
If deviations are detected (e.g. drifts), these density curves can provide you with details about the change, for example, whether you have to rerun linearization.