aionggandGuillem Hermida
3c6089bcfc
Per-ink coverage at a pixel and over a page, TAC per pixel, the pixels and connected regions over a TAC limit, and an sRGB composite of chosen plates: process plates through the printing condition, spot plates multiplied over them by their alternate's appearance. Ported from the data parts of pdfcraft #2770 separations.rs. Co-authored-by: Guillem Hermida <66697068+guillehr2@users.noreply.github.com>
craft-separations
Print separations for the Craft apps:
ink: the ink model the writers and previews share.InkSetholds the four process inks (always first, in plate order) and the spot inks of a job;InkColoris a colour as ink tints (Separation,DeviceN, registration or none);Overprintholdsop,OPandOPM. Spot names are compared as PDF names:/Gold#20FoilandGold Foilare one ink.plates: one 8-bit plane per ink (255 = 100% ink) rendered from a PDF page.cms: process colour conversion into a CMYK printing condition through craft-cms.
Plates from an exported PDF
An app exports its PDF as usual, then separates a page of it:
use craft_separations::{plates, InkId, Options, Process};
let p = plates(&pdf, 0, 150.0, &Options::default())?;
for (id, ink) in p.inks.iter() {
let plane = p.plane(id); // p.width × p.height tints, row-major
println!("{}: {} pixels inked", ink.name(), plane.map_or(0, |t| t.iter().filter(|v| **v > 0).count()));
}
let black = p.tint(InkId::process(Process::Black), 10, 10);
let gold = p.inks.lookup("Gold").and_then(|id| p.tint(id, 10, 10));
The plates are the PDF as printed, so a preview built on them shows what the writer produced, not what the document model intended.
How a plate is made: the page renders once per ink through craft-pdf's raster with
hayro-interpret's plate mode (InterpreterSettings::plate). Every paint draws its tint of
that ink as gray film. A paint that overprints (op/OP, and OPM 1 for zero DeviceCMYK
components) without naming the ink leaves the film as it is; with Options::overprint off,
every paint knocks out. Clipping, anti-aliasing, soft masks, transparency and knockout groups
stay the renderer's own. Separation and DeviceN colorants paint their own plates (All
every plate, None none), DeviceCMYK its components, DeviceGray black only.
Inks are found by a low-resolution pass that records each spot ink a paint uses, in the order first painted. Spot inks used only inside soft masks are left out. Each spot gets a Lab alternate measured from its sRGB appearance at 100%, so out-of-sRGB spots are clipped.
Process colour
RGB, CIE-based and ICCBased colours become CMYK through, in order:
- the CMYK profile of the page's or the document's output intent (a
GTS_PDFXintent first), when craft-cms can convert into it; Options::fallback: craft-cms's Coated FOGRA39 profile (the default), a profile the caller gives, or the ISO 32000-2 §10.4.2.4 device formulas.
Plates::conversion says which was used. Conversions are relative colorimetric without black
point compensation. DeviceCMYK, and ICCBased CMYK in the printing condition's own profile,
separate as they are.
Caps
| Constant | Value | Why |
|---|---|---|
MAX_SPOT_INKS |
32 spot inks per page | A DeviceN space has at most 32 colorants, and each plate costs a render and a byte per pixel. Further spots are listed in Plates::unseparated. |
MAX_PLATE_PIXELS |
4 MP per plate (2000 × 2000) | A page with many inks stays within a few hundred megabytes. The resolution is lowered to fit; Plates::dpi reports the one used. |
The renderer's side limit (craft_pdf::raster::MAX_SIDE) also lowers the resolution.
Approximations
- Non-separable blend modes and groups that blend in RGB are approximated per ink.
- The graphics state's rendering intent is not read; transfer functions and halftones are not applied.
Credits
- Plate mode, ink discovery and the output-intent handling come from storytold/pdfcraft#2770 by Guillem Hermida (guillehr2), with craft-cms in place of moxcms.
- Knockout groups in the renderer come from storytold/pdfcraft#2974 by mtlcl410.
Both MIT OR Apache-2.0, as this crate.