Seshat 1.9.0 checks print files against the official GWG standards
Seshat 1.9.0 checks files against the values the Ghent Workgroup publishes for each kind of print, measures total ink as the GWG specification does, and finds content in the registration colour.
A print shop should be able to say which standard a file must meet, and get a check that holds it to exactly that. Seshat 1.9.0 takes its values from the Ghent Workgroup's GWG 2015 specification, the published standard for exchanging PDF/X-4 files in print.
Presets for every kind of print
Send gwg_sheet_cmyk, gwg_sheet_spot, gwg_web_cmyk, gwg_web_spot, gwg_magazine_ads, gwg_newspaper_ads or gwg_newsprint as the preset. Seshat then checks with the values the specification publishes for that kind of print:
- total ink;
- smallest text and thinnest line;
- rich black text;
- resolution of photos and of line art;
- how many spot colours are allowed, and whether RGB pictures are.
Add _rgb to the name to allow RGB in pictures. The existing presets now take their numbers from the same specification and from the print profiles' own limits.
Total ink as the standard measures it
- The process inks, averaged over 15 mm. Total ink is the sum of cyan, magenta, yellow and black on the page as it prints, averaged over any 15 × 15 mm square inside the bleed. This is how the specification defines it. A tiny heavy detail no longer counts as a heavy area; a large heavy area still does.
- Spot colours are shown alongside. The same measure with spot colours added is reported next to it, for information.
- The check and the plates give the same numbers.
Registration colour in the page
The registration colour prints on every plate. It is meant for crop marks and register marks, never for page content. Seshat now reads the separated page to see where it really prints, with clipping and line widths as printed. It reports content in that colour, and the fix registration_to_black puts that content on the black plate while the marks keep it.
Rules as the specification words them
- Small text and thin lines: in a GWG preset they are judged only when they are white or made of several inks, because text and lines in a single ink print sharp.
- Rich black text: follows the limit of the kind of print.
- Line art (1-bit pictures) needs its own, higher resolution.
Also in this version
A colour defined under certain short names inside a PDF could make a whole page print blank in the separations. Seshat now handles those names, so such pages separate as they print.