[scribus] White versus transparent pixels question

[Marco]

Tnx for your input, I'm happy it matches my intuitive understanding of
how it could work.
In my past I have been on the customer or IT side of all the problems
related to printing, so CMYK, Pantone, ecc ecc are not new words,
however I never had a real direct contact with this interesting world.
I will give a try using spot colors with png images (and all related
conversions),  so far the workaround has been changing the white color
so that it is slightly different from the page color, then the pixels
are in the output.

Il 25. 04. 16 09:34, Vladimir Savic ha scritto:
> 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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