When you export a book for a printer, Charc converts its colour for the press and writes the file as PDF/X-1a. It does both with its own colour engine, which runs on our export server and in the Charc desktop app. That engine is built on the work below.
Press colour
FOGRA39 characterisation data from Fogra (Fogra Forschungsinstitut für Medientechnologien e.V., Munich). Charc’s press colour recipes (Charc Coated 240 and Charc Coated 300) and its grey curve for black-and-white interiors are based on this data, which describes how coated offset paper prints. Charc’s press files name FOGRA39 as the printing condition they were made for. Charc is not certified or endorsed by Fogra.
ArgyllCMS by Graeme W. Gill, used to build Charc’s press profiles from the FOGRA39 data. It is a tool we run when the profiles are made; no part of it is included in Charc.
Little CMS by Marti Maria Saguer, used through Pillow to turn the profiles into the lookup tables Charc’s colour engine reads. Also a build tool only.
In Charc’s exporter
This open-source code is part of the exporter, on our export server and in the desktop app:
- pdf-lib, copyright 2019 Andrew Dillon, with its standard fonts (copyright 2018 Andrew Dillon) and UPNG (copyright 2017 Photopea). MIT licence. Reads and writes every press file.
- pako, copyright 2014–2017 Vitaly Puzrin and Andrei Tuputcyn. MIT and zlib licences. Compression inside the PDF.
- jpeg-js, copyright 2014 Eugene Ware. BSD 3-Clause licence. Charc adapts two of its parts to read and write CMYK and grey pictures:
- the JPEG encoder, copyright 2008 Adobe Systems Incorporated, BSD licence;
- the JPEG decoder, copyright 2011 notmasteryet, from Mozilla’s pdf.js, Apache License 2.0.
The Mac app runs the same exporter inside its own WebKit, and carries a few more pieces for that:
- buffer, copyright Feross Aboukhadijeh and other contributors. MIT licence. With base64-js (copyright 2014 Jameson Little, MIT licence) and ieee754 (copyright 2008 Fair Oaks Labs, BSD 3-Clause licence).
- tslib, copyright Microsoft Corporation. 0BSD licence. Part of pdf-lib.
Licences
Each of these is used under its own licence, and Charc keeps the copyright notices and licence text with the code. Thank you to everyone who made and shares this work.
Something missing or wrong here? Write to [email protected].