[scribus] Color management settings

[Jean Ghali]

Le 10/07/2020 à 13:30, JLuc a écrit :
> Hello
> i looked at the Help about color management settings
> and cant find satisfying explanations.
> 
> The settings dialog lists various profile settings are about CMYK and RGB.
> I translate them here from french so it could be slightly different :
> 
> # CMYK images : asks for a CMYK profile
> 
> Is that the profile for CMYK inserted images ?

This is the default profile for CMYK images, ie the profile which is used if a CMYK image
has no embedded profile.

> 
> Does it mean ALL provided images should have this same profile ?

No.

> 
> When my files have different internal profileS, which profile should i choose ?
> 

Réponse de Normand : "Up to you". More seriously, if you target ISO Coated v2 or Fogra39,
you probably should use one of these two profiles.

> Or should we convert all images to a same profile before providing them to scribus ?

No, that's not needed.

> 
> Does the correct behaviour depends on the PDF-produced version choice 1.3, 1.4 or 1.5 ?

No.

> 
> Is there a simpler choice where i dont have to convert all images to a same CMYK profile ?
> 

As mentioned above, you don't need to convert all images to a same profile before
inserting them in your layout.

> 
> # CMYK colors : asks for a CMYK profile

> What use is that setting ?
> 

This is the profile used for solid colors, ie colors you define using Edit > Colors and
Fills menu (in 1.5.x).

> Is that related to "spot colors" for marketing and advertising professionals
> and i shouldnt care this as a book editor
> because i'm not interested in exact pantone truthfullness for charter or logos
> and all i care is nice looking photographs.
> 

No, "spot colors" have their own color space.

> # Printer : also asks for a CMYK profile
> 
> This is the printer profile.
> (FOGRA39 in my case)
> 
> # RGB images
> # RGB colors
> Same.
> 
> # About the UI
> 
> The checkboxes enable to choose
> - activate color management
> When this is checked :
> -- black point balance
> -- simulate on screen
> When this is checked :
> --- convert to printer colors
> --- display out of gamut colors
> 
> Does "simulate on screen" simulate anything when "convert to printer colors" is not checked ?
> Maybe this enables only the "display out of gamut colors" choice ?

The "Convert all colors to printer space" option has only an effect if the default
profiles for CMYK colors or images is different from the selected printer profile.

When "Convert all colors to printer space" option is unchecked, the simulation suppose the
CMYK values as defined in the document stay unchanged, are passed as is to the RIP then
printed. This is the most common workflow.

When "Convert all colors to printer space" option is checked, the simulation suppose a
completely color managed workflow, ie the ideal case for PDF/X. In this case the
simulation suppose the CMYK values as defined in the document are tagged with ICC
profiles, *converted* to the printer/press colorspace, passed to the RIP then printed.

So that's two printer output simulations for two different workflows.

> 
> (and also i'm curious to know : Why is there a black point balance and not a white point
> balance as usual ?)

The term balance is incorrect. There is no balance, just a compensation. The black point
compensation map the black point of the input color space to the black point of output
colorspace. When input colorspace has a much darker black point than the output
colorspace, this is generally the case when converting RGB colors to CMYK, the black point
compensation avoid dark colors to be clipped prematurely and consequent loss of details in
shadows.

There is no white point compensation because ICC workflows basically suppose the white
points of input and output colorspaces are mapped to each other. This comes more or less
from the way how device independent colorspaces used during calculation of ICC profiles,
CIELab or CIECAM02 usually, are defined.

Jean