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
