Color Management setup

These are practical notes to issue a PDF for printer, using RGB images, and having to issue a CMYK PDF.

You are supposed to have at least a very basic knowledge of : - what is CMYK, what is RGB - what is a color profile

Preamble
Color Management deals with how color is managed both in PDF output files and in image input files.

Setup is spread across three places:
 * Scribus preferences and document setup
 * Color pane in the export to PDF dialog
 * Little "color management" button in status bar

Scribus and Document Setup
These are the preferences for the PDF output file.

Beware ! When a document is created, it features the Scribus defaults ICC profiles. If later changing the default Scribus ICC profile, the document's own ICC profile dont change and the profile previously set through default scribus setup.

Color pane in the export to PDF dialog
First option is to specify the output type : either RGB (web) or CMYK (printer)

Then the "united colors" and "images" title options are to specify how to read images : input setup.

Color management button down in the statusbar
This controls all !



Whenever it is not pushed, no CM will occur.

PDF output
The PDF file format has several versions: 1.3, 1.4, 1.5, X-3 (and X-1, which is available in Scribus 1.5 svn).

Some versions of the format, such as X1, only include CMYK image files; other versions, like X3, accept mixes of RGB and CMYK.


 * PDF/X-1a: Blind exchange in CMYK + Spot Colors, based on PDF 1.3
 * PDF/X-3: Allows CMYK, Spot, Calibrated (managed) RGB, CIELAB, with ICC Profile, based on PDF 1.3.

When creating a pdf that only accepts CMYK, like PDFX1a, Scribus converts all RGB images to CMYK, using the provided color profile.

To create a CMYK-only PDF1.4 or PDF1.5 file, one has to:
 * Set up the correct ICC profiles in the document setup
 * Enable Color Management through CM button in the status bar
 * In the Color pane of the PDF setup dialog, select "printer" as output, and leave everything unchecked in that pane, particularly do not embed profiles for images.

PDF Readers
In Ubuntu, CMYK images are displayed poorly by both Scribus (on screen) and Acrobat Reader: Scribus display is too dull and dark, whereas Acrobat Reader display is too clear and bright. Evince displays CMYK colors correctly.

to be confirmed / investigated
In Ubuntu :

- why does pure CMYK yellow appear brownish when in font, but not when in images ? (and not in windows ?). Might be related to screen profile but why do text differs images ? - why is screen display different when color management button is ON, even when option "display on screen as color managed" is not clicked in setup ?