[Scribus] Colour Swatch and more questions

[Craig Ringer]

Cedric Sagne wrote:
> Craig,
> 
> After some research on your answer, I repeat my question about a way to know 
> from a physical "yardstick" what your colour will look like on paper, that 
> is on a specific type of paper assuming your printer uses it and does not 
> take liberties with it?

A swatch book is useful for this, but only if you're actually sending
true spot colours to the printer. It will not give you an accurate
indication of how the associated CMYK colour will look, since that is
only there as a rough approximation of the spot colour for preview purposes.

If you want to know how a specific CMYK colour will look on your press
and paper, ask your printers for a swatch sheet printed from the press
on the desired paper type. Some printers do this for a range of colours,
so designers can pick specific CMYK values and know how they'll look on
paper. Without this, as far as I know there IS no way to get such a
physical yardstick for non-spot colours.

See below for a detailed explanation of what a spot colour actually is,
and why it's not as simple as a specific CMYK value.

> Well actually I thought this was the purpose of such colour swatches, to get 
> a client to pick his colours there, and be sure the output will match.

That's correct. However, you can only truly rely on that if you're using
a named spot colour in your document. Putting the CMYK or RGB values
that approximate that spot will not guarantee accurate reproduction,
because (eg) CMYK (40,20,10,4) one press is different to CMYK
(20,40,10,4) on another press.

> I know Pantone publishes colour swatches which may be used to order specific 
> inks (then inserted as spot colours), but could you then tell me which tool 
> makes a link between a colour on the screen and the coding used there

[Here's my explanation. It should be accurate, but I'd very much
appreciate comments/corrections.]

In Scribus, when you create a spot colour, it's identified by a name
like PANTONE5512. You also provide a colour value in CMYK or RGB, but
this is used only for preview purposes, or to export to media where spot
colours are not supported or not used.

Normally, when you send a job to a printer, you send a PDF. If you're
using spot colours, Scribus specifies the colours *by* *name* in the
PDF. Instead of saying "CMYK(40,20,10,4)" it'll say "MyColour". It's
possible to pick whatever names you want, so long as you tell the
printer what you want them to print those colours as (think: gold ink,
varnish layers, etc). In most cases, however, you'll use widely
recognised spot colour names from ranges like PANTONE, so the printer
will already know what you want the spot colour to look like, and will
have their equipment calibrated to produce an accurate match for those
colours.

The key point is that spot colours are specified by name, not colour value.

You can make the preview colour in Scribus bright pink, and your
document should come out of the press with the correct spot colour
anyway - so long as the printer RIPs the document with a RIP that
supports spot colours and is configured to use them. Scribus still
includes that preview colour in the PDF so that devices that want to
process the PDF but don't know what the spot colour name means can still
handle it. This means that if you use bright pink for the preview colour
associated with your "Varnish" spot colour, it'll look bright pink in
(eg) Adobe Reader, but your printer's RIP (which will have been told
what the name "varnish" means) will process the "Varnish" colours into a
separate plate that will then be printed with varnish.

This means that your printers are very important for spot colour
reproduction. Some spot colours can be reproduced using 4-colour
halftones on certain media, so if your printer is calibrated for those
spot colours it'll be able to reproduce them in normal 4-colour
printing. However, the printer and RIP still need to be calibrated for
those colours - they can't just use the CMYK preview values. Other spot
colours can not be reproduced in the 4-colour gamut of most presses -
they need special inks. For those, your printer must use an extra plate
for the spot colour, something that usually costs extra and must be
pre-arranged.

My point is that you can't just put a spot colour in and assume that it
will work. You need to find out from your printer what you can and can't
use, and how you should do it.

> which 
> I don't care if it looks good or not (and calibrating a monitor is NOT an 
> option because I work on a general market laptop screen) 

One of the advantages of using spot colours is that you don't have to
care in the slightest how it looks on screen, or worry about
calibration. So long as the output device (commercial printing RIP, high
end laser printer, etc) is properly calibrated for the spot colours
you've used, you're fine.

--
Craig Ringer