[scribus] Lighten dark colors

[JLuc]

Le 10/07/2020 à 09:56, JLuc a écrit :
> Printed photos are not too bad but are quite often too contrasted
> and dark areas appear flattened and shifted to the very dark.

Looking in the mail archives i found that Victor once wrote
« I had a similar problem with 1.5.0svn when preparing PDFs for offset printing.
Images was dimmed - they looked like you looking at them through fog.
I solved that problem by:
1. converting all jpgs to CMYK TIFF
2. turning on color management and applying color profiles when exporting to pdf. »

So i've tried doing it : took a set of too-dark-rendered sRGB JPG images
and converted them to CMYK TIFF using FOGRA profile
(convert "$input" -profile theforgraprofile.icc "$radical.tiff")
and then opened my eyes to various setting effects :


- with image viewer (both gpicview and gthumb) :
Converted tiff images look darker on screen when opened.
They look closer to what is realy printed.
That's rather satisfying because it enables to work not so blindly.


- when used in scribus :
Depending on the color management display setting they also look darker or not :

   - with CM disabled, RGB jpg and CMYK tiff look the same.
     I'm surprised that tiff arent darker than JPG as they do in image viewer.

   - with CM on and no screen rendering, they look the same also

   - with CM and screen rendering ON, both RGB JPG and CMYK TIFF look clearer and dimmer.

   - with CM and screen rendering and "convert all colors toward printer's colorspace" ON
     Same as without option. I dont understand that option.

   - with sames options AND "black point balance" ON
     the RGB JPG appear the same, but the CMYK TIFF appear darker AND slightly crispier.

- produced PDF viewed with evince

    - With colour management ON, both with and without "black point balance" look the same.

    - without colour management,
	RGB JPG look very slightly lighter thant with colour management
	no change for CMYK TIFFs


FYI i uploaded the tested files here :
https://covid19.framadrop.org/lufi/r/HNf4VaZL5P#snyh6tpPaCMKKgYlls+4aR5oI20huR9NC/v476wMyAQ=

For future works i'm not sure how i should behave now.

When last printing, I did use the "black point balance" option.
I wonder if it's partly responsible for darkening and flattening dark areas.

I could convert all JPG to TIFF to have a slightly better screen rendering
and be slightly better able to edit files so as to fix issues...
but isnt scribus supposed to feature a nice workflow for JPG also
when provided with correct printer color profile ?

I could also buy a profiled screen
but i dont like such solutions as "when it doesnt work buy something more expansive"
which at its best would help me understand the issue but not avoid it.

Because in the end i feel the issue is mostly with my source photographs :
most are not professional photographs but cheap camera or smartphone photos
taken by "normaly unprofessionnal" people and the dark and lights are badly balanced
but I have no other choice than using them.

Until now i have managed to edit these pictures so they are not too bad on screen
but i'm afraid i cant improve them more so as to fit this obscure printer rendering.
It means that trying to do so will greatly reduce my photos possible choices.
That's why I'd prefer to manage the contrary : enable printer to print as displayed.
When possible...

JL