[scribus] White versus transparent pixels question

[Vladimir Savic]

Every color you want to print will add on top of another. If you print
yellow and lay down some blue on top of i, you'll end up with some shade of
green. You can do that as many times as you want and the result will be
always a step closer to a "rich" black. Normally, for acceptable
cost/efficiency ratio, we have CMYK (cyan+magenta+yellow+k) standard. Look
at Wikipedia for more information about it. You have hit the problem of
base color. It is simply assumed that underlying color is paper's white.
Everything is being build on top of it, quite literary.

Of course, you are not the first having an idea of printing on top of some
other color. Therefore, printers started using white pigment for making
special - white - color. Note the word Special here. We will return to that
soon. If you don't specify that you want old, timed, recycled, yellowish
paper, printers (both the people that operate printing presses and desktop
printers) will ASSUME you want it printed on plain white paper. If you
don't want that to happen, you should then go to a printing press operator
and handle your "special" paper to him. But, at that moment he makes one
more ASSUMPTION for you and that is that you want it to be printed using
CMYK method. Computer programs for prepress make those two assumptions for
you too. The background on your working canvas in Scribus is white -
non-printabe. And the colors you use are in CMYK.

What if you want to give printer your toothpaste, shoe polish or your
favourite perfume to print with that? It's possible, but you will not get
desired results with CMYK, of course. You have to define SPECIAL case. It's
the same with your white. In Scribus you should define specal color, called
Spot color, name it "White", and use it to fill objects with it. That's
already covered in detains in many other places. Part of it has been
documented in official documentation under Color Palettes.

What is also very important to you here is that it seems that white
background of an image is being treated in two ways:
1) Exactly as transparent, when put on canvas directly. There is no
distinction if your image has transparent background or not.
2) Removing other colors underneath it, when placed on top over some other
Scribus' item. Now there is a distinction. If your image contains
transparent pixels, underneath objects will appear where transparent. If it
were opaque, white background of your image will expose paper color at that
places.

In reality, white just exposes paper color.

Hope this helps...

On Sun, Apr 24, 2016 at 10:17 PM, Marco <marco.brignoli at marcobaldo.ch>
wrote:

> I'm sorry, my answer in this phase is "I don't exactly" as I need to
> create a sample file to ask for some offers.
> What is given is the paper to be used, a colored facsimile of old time
> paper (rough, thick, etc ).
> Generically speaking any typographical device that can print in white on
> this support is a potential candidate for me.
> I'm really not a professional in this field, just the standard IT guy
> with some friends needing support for a no profit organization....
>
> I have been exploring the problem a little bit today, and my
> understanding so far is that there is somewhere in the code an "IF
> pixel_color = page_color THEN skip ELSE send_to_output" than cannot be
> bypassed. If this is true (?) I can put in the output all the colored
> pixels of an image by choosing as page_color a color not used in my
> document. I'm not sure of this, it is just my current hypothesis.
>
> Il 24. 04. 16 20:45, Vladimir Savic ha scritto:
> > This is actually one quite interesting question. You haven't told us the
> > most important thing and that is - how do you plan to print that
> material.
> > What equipment is involved in printing process? We have to start from
> there.
> >
> > On Sun, Apr 24, 2016, 20:08 Marco <marco.brignoli at marcobaldo.ch> wrote:
> >
> >> I'm a new and really happy user of Scribus. It works like a charm with a
> >> few hours of self-learning, supported by the nice on-line documentation.
> >>
> >> I have just a problem I can't solve with a document containing an image
> >> having a white object on a transparent background (and some yellow
> text).
> >> As the final result of my work has to printed on not-white paper all the
> >> white pixels of this image will have to be in the output (printer or ps
> >> file).
> >> Currently the white pixels are discarded, I can see this in the preview
> >> of the print menu with the transparency option enabled, as the white
> >> pixels are shown as they would be transparent. By changing the white
> >> pixels to any other color this problem disappears.
> >> Can anyone please be so kind as telling me how I can have also the white
> >> pixels explicitly in my output? It is maybe trivial, but I could not
> >> find the appropriate switch....
> >>
> >> Tnx in advance for your help.
> >>
> >> Marco
> >>
> >>
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