Press compensation from measurements

Dots print larger than they are on the plate. A press compensation curve makes up for it: you print a test form with tint ramps, measure what came out, and the app computes the plate dots that make the printed sheet reach the aim you choose. The result is an entry of a press compensation curve (see Plate curves).

The curve you get#

For each separation, your measurements say what the press printed at each tint. The curve is the plate dot that makes that tint print the aim you chose. Repeated readings of the same tint are averaged. A reading that falls back is smoothed, so the curve keeps rising.

Enter measurements by hand#

In the curve editor, choose the separation's tab and From measurements:

• Plate % and Measured: one row per patch of the ramp, up to 200 rows. + Row adds one.
• Measured as: Tone value % (0–100), Fraction (0–1) or Density. For densities, the first row is the paper and the last row the solid, and the values are turned into tone values from them.
• Aim: what the print should reach (see below).
• Test form printed through: the curve the test form was printed with (see below).
• Smooth with the TVI model: use this when the readings jump around. The curve follows their overall shape instead of every point.

The chart shows the measurements as dots, the aim as a dashed line and the resulting plate curve. It refreshes a moment after you change a field and leave it. Save version keeps it.

Import measurements#

Import measurements takes a whole measurement at once:

1. Paste the text into the box: CSV, TSV or CGATS, up to 256 KB.
2. Under Values are, keep Detect or say what they are.
3. Choose the Aim.
4. Press Compute compensation.

Every measured column becomes the "From measurements" entry of the separation with that name, keeping the limits the entry already had. Check the notes under the box, then Save version. The pasted text is kept with the new version, as a record of what it was computed from.

Formats#

CSV and TSV. An input column (the tint of each patch, in percent or as fractions from 0 to 1), then one measured column per separation. A header row names the separations; without one, the first measured column is Default and the others Column 2, Column 3 and so on. Commas, semicolons, tabs or spaces separate the columns (decimal commas work with semicolons and tabs), % signs are ignored and lines starting with # are skipped.

input,Cyan,Magenta,Yellow,Black
0,0,0,0,0
25,39,40,38,41
50,67,68,66,70
75,88,89,87,90
100,100,100,100,100

CGATS.17. Measurement files with CMYK_C, CMYK_M, CMYK_Y and CMYK_K inputs and density fields. Single-ink ramps are found from the rows where only one ink is set, and the paper row is shared. The densities read are:

Detect reads values above 3.5 as tone value percent, values from 0 to exactly 1 as fractions, and anything else as densities. CGATS files are always read as densities unless you choose otherwise.

The import notes what may need a look: fewer than 5 points, a ramp without 0 and 100 %, inputs that don't increase (repeats are averaged) and measured values that go back down (they are smoothed).

Aims#

The curve the form was printed through#

A test form is often printed with a curve already in place. Measured through that curve, the press looks different than it really is, and a new curve computed as if the plates were linear would be wrong. Choose that curve under Test form printed through, and the app works out the new curve on top of it. Choose No curve (uncalibrated) when the form was printed linear. The choice is saved with the version.

Not supported yet#

• ISO 18620 curve files can't be imported or exported from the app.
• Aims are per separation: neutral print density (gray balance) aims aren't offered.