A plate curve decides which dot a tint in the file becomes on the plate, separation by separation. It is how you compensate for dot gain on press, hold the smallest dots a plate can keep, and linearise the platesetter. A profile without curves screens linear: a 40 % tint in the file is a 40 % dot on the plate.
Curves are listed under Curves on the Profiles & curves page. New curve makes a blank curve or starts from a built-in one; open a curve to edit it.
The curve chain#
Every printed separation goes through up to four steps, in this order:
- Tone curve: an optional change to the tone itself.
- Press compensation: makes the printed sheet reach its aim despite dot gain (see Press compensation from measurements).
- Limits: keep 0, min dot, max dot and keep solid, in plate-dot percent (below).
- Plate linearisation: corrects the platesetter, so the plate's dot is the dot asked for.
A profile's Tone curve, Press compensation and Plate linearisation fields fill the chain for every separation. A separation can also pick one curve of its own, in the profile's Screens table or in a job's separations table: it replaces the step of its own kind, and the other steps stay. Solid and technical inks get no curve.
The chain in use is named under the Curve field of each separation, such as "Press 150 v3". A chain that works out linear isn't recorded at all.
A curve keeps its kind (Press compensation, Plate linearisation or Tone curve), and each profile field only lists curves of its kind.
Warning: New curves are press compensation curves
New curve always makes a press compensation curve, and the editor can't change the kind. Tone curves and plate linearisation curves can be made through the API only for now, so the profile's Tone curve and Plate linearisation fields stay empty until you make one there.
One entry per separation#
A curve holds one entry per separation, shown as tabs: Default, and any you add with + Separation (Cyan, Black, a spot…). "Separations without their own entry use Default." Remove this separation deletes an entry. An entry's name must match the separation's name exactly, including case: an entry named "cyan" doesn't apply to Cyan.
Each entry is one of:
- Linear: no change.
- Points: a table of In % and Out %, from 2 to 33 rows. Inputs must increase from row to row and outputs
must not go down: a plate curve has to be monotonic. Paste
in, outpairs, one per line, to fill it at once. - From measurements: a press compensation computed from a measured test form (see Press compensation from measurements).
The chart shows the entry you are editing with its limits: the plate curve, the aim as a dashed line, and the points or measurements as dots. "Across: file %. Up: plate % for the curve, printed % for measurements." Under it are the values at 0, 5, 10, 20 … 80, 90, 95 and 100 %.
Limits#
Every entry has limits, in plate-dot percent, applied after press compensation and before plate linearisation:
| Field | What it does |
|---|---|
| Keep 0 below (%) | File values at or below it never image. At most 0.389 %, just under the smallest 8-bit step (1/255). |
| Min dot (%) | The smallest dot that holds on the plate or press, up to 10 %. |
| Below min dot | Hold (bump) lifts smaller dots to the min dot, blending back into the curve over the bump range: the usual flexo bump. Cut off drops dots below the min dot to paper. |
| Bump range (%) | The file range, up to 50 %, over which a hold blends back into the curve. |
| Max dot (%) | The largest dot below solid, from 50 to 100 %. |
| Cutback range (%) | The file range below 100 %, up to 50 %, whose tones are eased onto the max dot. |
| Keep 100 % solid | On: 100 % stays solid. Off: solids are screened at the max dot too. |
The chain takes its limits from the press compensation curve's entry, or from the tone curve's when the press curve sets none. Limits on a plate linearisation curve are not used.
Versions#
Save version saves the curve as a new version, with an optional note; a version never changes afterwards. The Versions list shows each one with its date and note; Restore makes an older one current again, as a new version ("Restored version 2").
A job that hasn't started uses each curve's current version, and the chain is recomposed whenever you edit the job. Screen plates freezes it: from then on the job, its report and its plate labels keep that version and its checksum, whatever happens to the curve later. A re-screen starts from the same settings but takes each curve's current version again.
Made for#
Made for says which jobs a curve suits. Printing condition and Device are for your reference. The others are checked against every job that uses the curve:
- Resolutions (dpi): one or more, such as
2400, 2540; empty is any. - lpi from and lpi to: the rulings of AM separations.
- AM and FM: the screen types.
- Polarity: any, positive or negative.
A job outside these limits either gets a warning or cannot be screened: the check says what is outside, such as "Curve Press 150 is not made for resolution 1270 dpi".
Built-in curves#
New curve › From a preset starts from one of these. They set limits only: a built-in gain curve would be made up.
| Built-in curve | What it sets |
|---|---|
| Linear | A straight line: plate % = file %. |
| Flexo bump 2 % | Keep 0 below 0.3 %; Min dot 2 % (hold), bump range 10 % |
| Flexo bump 3 % | Keep 0 below 0.3 %; Min dot 3 % (hold), bump range 12 % |
| Max dot 96 % (tone reversal) | Max dot 96 %, cutback range 8 % |