[XeTeX] cmyk encoded files

Zdenek Wagner zdenek.wagner at gmail.com
Mon Nov 21 00:56:34 CET 2011


2011/11/20 Daniel Greenhoe <dgreenhoe at gmail.com>:
> Thank you for the color information. It just seems that there should
> be a color printing standard that print houses strive to follow and
> that someone would produce a booklet based on that standard.
>
> I saw this in a document from one print house:
>
> "Consumer quality printers have a wide margin for variation. The best
> way to verify the final color output, when submitting a file to a
> printer, is to purchase a Pantone to Process Swatch booklet from a
> local professional art supply shop. This book contains Pantone
> calibrated color swatches that you can compare to the CMYK color
> percentages of your digital file"
>
> But if there is no "professional art supply shop" around, where does
> one find such a booklet?
>
This information is a bit misleading. As I wrote, Pantone are custom
colours that cannot be printed with CMYK, they can only be
approximated. Such swatches are useful if you have to approximate a
Pantone colour with CMYK. It sometimes happens.

However, colour printing is a bit science and a bit art. What you see
is light reflected by the printed page. The light is reflected by the
paper and some wavelengths are subtracted (absorbed) by the inks. What
remains is perceived by your eye and your brain perceives it as some
colour (colour is not a physical property, it exists only in our
brains). If I neglect subjective perception by our eyes and brains,
the colour is determined by the printed ink, by the paper and even by
the light. It makes little sense to search for CMYK percentages before
you select a paper. It happened to me just a few months ago. I had to
typeset a poetry book for children with a lot of colour pictures. The
publisher did not ask my advice and selected a paper with a beautiful
structure that would be very nice for a poetry book but absolutely
unsuitable for colour pictures. Fortunatelly they printed just one
sample book that had to be thrown to a trash. In offset printing the
inks are not applied all at the same time but sequentially. Thus the
printed page consists of layers. The order influences the resulting
colour. Thus if you buy swatches, you should know the paper used, the
order of colour printing, the ICC profile used (this corresponds to
the ink types). For instance, in European print houses different CMYK
inks are used in comparison to USA but even in Europe some printer
houses may use US inks. This is important to know before you convert
colours to CMYK. Some print houses offer ICC profiles for their
devices for free. And of course, when looking at the swatches, you
have to use a standard light. Standard bulbs can be bought in art
shops. Good print houses have them installed in customer rooms so that
a customer can see a printed sample properly.

Some print houses are reliable and you know that they will always
print the same document in the same way with the same colours, some
are unreliable. In good print houses you can always ask for printing a
sample, in the really good ones they even do it for free. There are
also companies that can produce a custom CMYK ICC profile. You have to
print a standard sample on the same device and the same paper and they
will measure it by a spectrometer and give you an ICC file. It may
cost some 50 $ but if you produce an expensive book, it is worth that
money.

I do not use custom CMYK profiles. First I calibrated my flatbed
scanner using an IT8 target supplied with the scanner. Then I
calibrated my inkjet by printing IT8 and measuring it by the
calibrated scanner. All this can be done by VueScan (www.hamrick.com).
My screen is not calibrated but I can compare a color table on screen
with the same table printed on my calibrated inkjet. Now when I take a
photo with my digital camera and have it printed in a photolab, I get
exactly the same colour as on my screen. I played a bit in order to
find an ICC profile that I could plug into LCMS for conversion to
CMYK. Now when I have a document prited by offest or by a digital
machine, I get the same colour as on my screen. Thus I have a standard
production chain: scanner - screen - inkjet - offset - digital
printer.

And where to buy all the things? I found an internet shop in our
country that sells swatches, standard bulbs, textbooks, software and a
lot of other useful things. You may find one in your country.
>
> On Sun, Nov 20, 2011 at 10:34 PM, Zdenek Wagner <zdenek.wagner at gmail.com> wrote:
>> 2011/11/20 Daniel Greenhoe <dgreenhoe at gmail.com>:
>>> 2011/11/20 Zdenek Wagner <zdenek.wagner at gmail.com>:
>>>> Printed colour samples are commercially available.
>>>> They are printed on different types of papers and CMYK values are given.
>>>
>>> Is there any such thing available in book form? That is, could you
>>> make a recommendation? Here in Taiwan, there is something commonly
>>> sold called Pantone彩色聖經 (Pantone Cai3Se4 Sheng4Jing1 = Pantone Color
>>> Bible). I did finally locate one in a bookstore yesterday, but it was
>>> sealed up and I wasn't allowed to open it without buying it.
>>>
>> Hard to say but Pantone is not exactly what you need. I bouhgt some
>> small samples here in the Czech Republic, this is a link:
>> http://www.dtpstudio.cz/vzorniky/cmyk/basic
>> Using CMYK just limited colours can be printed. The colours are
>> obtained by subtractive mixing, therefore saturated colours cannot be
>> printed. You can only print colours that fall into the CMYK gamut. If
>> you do not print in full colour but need only one, two or three
>> colours, custom colours can be used. This is the time when you can use
>> Pantone. Often company logos are designed using custom colours. You
>> can also find CMYK approximations of custom colours, it may be in the
>> Pantone Bible. When using a custom colour, it need not be necessarily
>> 100%, for instance the cover if this book was printed with the
>> following three colours: Blue GS 4C12, Red GS 3C41, Black. This is the
>> link to the book:
>> http://www.canopus.cz/dilo_ps/ps.html
>>
>> Hope it helps
>>
>>> Dan
>>>
>>>
>>>
>>> 2011/11/20 Zdenek Wagner <zdenek.wagner at gmail.com>:
>>>> 2011/11/20 Daniel Greenhoe <dgreenhoe at gmail.com>:
>>>>> 2011/11/20 Zdenek Wagner <zdenek.wagner at gmail.com>:
>>>>>> No.
>>>>>
>>>>>> LCMS is a good choice.
>>>>> LCMS is "Little Color Management System"?
>>>>> (http://www.color.org/opensource.xalter)?
>>>>>
>>>> Yes.
>>>>
>>>>>> 1. It ensures that the colours you specify in the document will be converted to cmyk.
>>>>>> However, the corrections are wrong.
>>>>>> 2. xcolor does not look into inserted graphics,...
>>>>>
>>>>> But what if I hand define all my colors using cmyk syntax like this for example
>>>>>     \definecolor{magenta}{cmyk}{0,1,0,0}
>>>>> and create all my graphics using pstricks and related packages (with
>>>>> no inserted graphics)?
>>>>> Then won't the resulting pdf be cmyk compliant and contain exactly the
>>>>> colors I defined?
>>>>>
>>>> That's what I do. Printed colour samples are commercially available.
>>>> They are printed on different types of papers and CMYK values are
>>>> given. Thus you select the required colour on a proper paper and use
>>>> it. Sometimes I select the colour in gimp and then using LCMS convert
>>>> the values from RGB to CMYK. Scanned images are also easy. I keep them
>>>> as TIF, using LCMS convert them to CMYK and then by tiff2pdf to PDF
>>>> that can be included by \includegraphics.
>>>>
>>>>> Dan
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> 2011/11/20 Zdenek Wagner <zdenek.wagner at gmail.com>:
>>>>>> 2011/11/19 Daniel Greenhoe <dgreenhoe at gmail.com>:
>>>>>>> Print shops often require pdf files containing color to be encoded
>>>>>>> using CMYK colorspace values.
>>>>>>>
>>>>>>> Version 2.11 of the xcolor package says that cmyk is "supported by
>>>>>>> Postscripts directly" (page 8). So if I simply specify
>>>>>>>  \usepackage[cmyk]{xcolor}
>>>>>>> in the preamble and compile with XeTeX/XeLaTeX, is that sufficient to
>>>>>>> ensure the resulting pdf is cmyk encoded?
>>>>>>>
>>>>>> No.
>>>>>>
>>>>>> 1. It ensures that the colours you specify in the document will be
>>>>>> converted to cmyk. However, the corrections are wrong. If you wish to
>>>>>> convert the colours properly, you have to use colour profiles. LCMS is
>>>>>> a good choice. Useful ICC profiles come with different products as
>>>>>> Adobe Reader, colour printers, scanners etc. They can also be
>>>>>> downloaded from the web. Calculations in the xcolor package can only
>>>>>> be used if you are satisfied with approximate colours. It is written
>>>>>> in the documentation that conversions are device dependent.
>>>>>>
>>>>>> 2. xcolor does not look into inserted graphics, you have to convert
>>>>>> your images to cmyk separately. Again LCMS is a good tool for this
>>>>>> purpose.
>>>>>>
>>>>>>> Secondly, is there any free utility available for checking the
>>>>>>> colorspace encoding of pdf files (maybe similar to foolab's pdffonts
>>>>>>> for checking embedded fonts).
>>>>>>>
>>>>>> I have not found any. Since I produce PDF files for printing very
>>>>>> often, I calculated that commercial Adobe Acrobat is cheaper than the
>>>>>> risk of paying unusable books, thus I have bought it.
>>>>>>
>>>>>>> Many thanks in advance,
>>>>>>> Dan
>>>>>>>
>>>>>>>
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>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> Zdeněk Wagner
>>>>>> http://hroch486.icpf.cas.cz/wagner/
>>>>>> http://icebearsoft.euweb.cz
>>>>>>
>>>>>>
>>>>>>
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>>>>>
>>>>>
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>>>>
>>>>
>>>>
>>>> --
>>>> Zdeněk Wagner
>>>> http://hroch486.icpf.cas.cz/wagner/
>>>> http://icebearsoft.euweb.cz
>>>>
>>>>
>>>>
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>>
>>
>> --
>> Zdeněk Wagner
>> http://hroch486.icpf.cas.cz/wagner/
>> http://icebearsoft.euweb.cz
>>
>>
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-- 
Zdeněk Wagner
http://hroch486.icpf.cas.cz/wagner/
http://icebearsoft.euweb.cz



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