[Scribus] Re: Crop mark

[Craig Ringer]

On Sun, 2005-09-18 at 21:56 +0200, Christoph Sch?fer wrote:
> Hi Asif,
> 
> > All of it flew past over my head!  I don't understand anything about
> > crop marks.  Would you elaborate more on it please?  Further, what is
> > "Bleeding" stuff?  Just out of learning and curiosity.
> 
> 
> all these features are necessary for professional printing, which is 
> quite different from printing on your inkjet.
> In most professional printing processes, content is printed on larger 
> sheet than the page with the content. To get the best results and to get 
> around some inaccuracies of printing machines, lots of different marks 
> need to be printed on these sheet, which have nothing to with content:
> 
> 1) Crop marks: Since the sheets are larger than the intended page size, 
> they need to be cut (cropped) after printing. Crop marks tell the 
> printer exactly where to cut.
>
> 2) Centre marks/fold marks: In most cases, the printed sheets will be 
> folded, and the printer needs to know exactly where.
>
> 3) Registration marks: These marks allow the printer to control if the 
> content has been placed accurately on both sides of a sheet.
>
> Other things might also need to be printed, such as a colour scale, a 
> densitometer scale or backup registration. All these things are 
> neccessary for the highest degree of control in the printing process.

Many preflight tools and/or RIPs generate these automatically now, so
you should generally check what your printer requires you to add. It's
increasingly common to simply be required to provide a PDF with a
(usually 10mm) border for bleed.

The printer my work uses rejects jobs with marks added. Their tools do
it automatically, adding marks that their press and post-printing gear
will recognise and handle. They use this for adjusting ink flow during
printing, automatically trimming pages, monitoring registration during
printing, and more. It's all rather impressive, actually - and
customer-added marks just get in the way.

> As for bleed, this has also to do with little inaccuracies of printing 
> machines. Imagine you want to have a photo on a page that is to end 
> exactly at the page margin. For that reason, you add additional space 
> (mostly defined by the printer) and drag the photo a bit over the "real" 
> page margin. That way, you can be sure that the photo really ends at the 
> page margin and there is no white space left, due to inaccuracies of 
> printing machines. Most professional graphics and layout programmes have 
> a "bleed" function that lets you enter the values required by the 
> printer. Scribus doesn't have this feature yet, so you need to follow 
> Louis' advice on the Wiki.

This also helps ensure that there's no tapering off of the colour at the
edges, printing inaccuracy aside. Here's my (probably rather limited)
understanding: 

With many printing technologies, ink "bleeds" into a page - each dot
expands from where it's printed. With newspaper litho printing this is
as much as a 30% expansion, so it's pretty significant. If the printer
was to stop exactly at the edge of your page, you might get a frayed
looking edge from where dots didn't quite make it onto the page, but
they would have expanded well onto it. By printing a small amount
outside the borders where the page will be cut, this problem is
eliminated. My understanding is that it only matters for edge-to-edge
printing (flyers, gloss magazines, brochures, etc).

--
Craig Ringer