[scribus] No real CMYK black possible??

[Louis Desjardins]

Tino Schwarze a écrit :
> Hi Andreas,
> 
> On Sun, Jun 22, 2008 at 07:12:41AM -0700, avox wrote:
> 
>>> I'm currently designing a folder with black background. I'm using
>>> the ISOCoated v2 (ECI) profile for offset printing. But my black (as in
>>> CMYK=0/0/0/100) background doesn't look black at all on screen. Scribus
>>> as well as Acroread display a very dark grey and I can even distinguish
>>> it easily from the pictures I converted from sRGB->ISOCoated using
>>> tifficc. (Pictures converted by scribus are also okay and visibly darker
>>> than my supposedly-black background.)
>>>
>>> I tried unchecking Blackpoint compensation - no visual difference. I've
>>> set the rendering intent to "relative colorimetric" and exported to
>>> PDF/X with ISO Coated v2 destination profile. I also tried PDF1.4
>>> without profiles (with Printer as destination) - same result.
>>>
>>> How will I get a real black color?
>>>
>>> Scribus version is 1.3.3.11, running on SuSE 10.3, liblcms is 1.16.
>>>
>>> I've got a workaround: made a 10x10 black TIFF, converted to ISOCoated,
>>> used it as background but the print shop will probably complain about
>>> too low resolution.
> 
>> CMYK 0/0/0/100 isnt the blackest black in CMYK space, so colormanagement
>> maps it to a dark gray in RGB space (as used by your monitor).
> 
> Okay.
> 
>> There's also Rich Black (eg. 40/40/40/100) and Total Black
>> (100,100,100,100),
>> but the latter is rejected by many printers because it uses too much ink.
> 
> 
>> In Scribus it would work best to create an RGB black (0,0,0) and rely on 
>> colormanagement to convert it to the darkest CMYK black available in the
>> target color space.
> 
> Hm. Something strange is happening here. Please have a look at:
> http://www.spiritualdesign-chemnitz.de/tmp/blacktest.tar.bz2
> It has the following files:
> blackbg.tif - 10x10 RGB TIFF without any profile
> blackbg-ISOcoated.tif - 10x10 CMYK ISOCoated v2 TIFF created via
>   tifficc -i sRGB\ Color\ Space\ Profile.icm -o ISOcoated_v2_eci.icc -c2 -e -b -t1
> schwarztest.sla
> schwarztest.pdf - PDF created from sla via "Printer" PDF 1.4 export, no
> profiles used
> schwarztest-bp.pdf - PDF created from sla via "Printer" PDF 1.4 export,
> no profiles used, but blackpoint compensation turned OFF in document
> properties
> 
> The point is: The image created by tifficc is really black. The same
> image converted by Scribus does not show up black in Acroread nor Scribus.
> Neither do the "black" colors. To make things worse, the black from the
> RGB image is not the same as the black from the RGB color! The image's
> black is even lighter. If I disable blackpoint compensation, the RGB
> image shows up black in Acroread. Is there a bug in Scribus or tifficc?
> Since I created the ISOCoated image with blackpoint compensation enabled.

If you’re going to work in CMYK, then work in CMYK. Working in both RGB 
and CMYK will result in some frustration. Especially when you need to 
match a color in CMYK from an image in RGB.

Because you need to create a specific black to match the one (the ones?) 
in your images, I would strongly suggest that in that particular case 
you first convert your image to CMYK and then read the values of the 
black you’re looking after in that image and that you want to match. 
That way, you will know for sure the values in all 4 CMYK plates and 
you’ll be able to create this black in Scribus to match the black of 
your image.

It is very tricky to match a black in an image and use this as a 
background or an adjacent color to this image. It is very unlikely that 
the black in the image will be consistent throughout the whole image. 
What is seen by your eyes may well be an array of blacks.

As an additional note, please make sure that you don’t come up with a 
black made of 100/100/100/100 CMYK... The *only* color that can have 
such values is the Registration color, for registration marks.

Depending on the profiles embedded into the image, the onscreen 
rendering of the image can differ from the color created by Scribus. The 
reality check is the CMYK output, the actual values that will be 
reproduced on the plates. If they match in your image and in your 
Scribus color, then they will print the same. A final contract proof 
will confirm this.

HTH

Louis

> 
> Bye,
> 
> Tino.
> 
> PS: Is there some Linux program to load a CMYK PDF and check the CMYK
> values?