JDF & production related data
Most of the 1000 or so pages of the JDF specs deal with describing production settings for each step that is needed to produce a job. A JDF file does not have to contain all of these production settings since there are no systems on the market that are aware of every single setting needed to produce a job.
An application such as an MIS system may be aware of the general steps that are needed to produce a certain job but it may not know the actual settings for each phase. A JDF mechanism called Gray Boxes was implemented to cope with such circumstances. Using Gray Boxes, a system can describe roughly what needs to be done, without going into detail about the technical specifics of a certain production step, nor the exact order in which processes need to follow each other.
Let’s take a look at the different production steps that an order usually goes through.
When a job is printed, the press will not print each separate page, like a laser printer of inkjet printer does. To speed up the process and cut cost a printing press prints a number of pages (often 4, 8 or 16) at the same time on a large press sheet. The process to determine how pages are best combined on a press sheet is called imposition.
There are different ways in which the imposition can be defined within a JDF file, depending upon the level of knowledge that a certain system has about impositioning pages.
- Imposition programs have a very detailed knowledge about the ways pages should be positioned on a press sheet, which press marks need to be added, gutter distances,… Such system can use a JDF mechanism called JDF Layout to define exactly how a job needs to be imposed. This information can be read by a prepress system to actually impose pages and create film or plate data. Since JDF is not a page description language, a JDF file can contain a description of the press sheet geometry but it cannot contain actual graphic elements such as the crop marks or color bars. To get around this limitation a JDF layout file contains a link to one or more separate PDF pages which match the press sheet size and which contain all of the crop marks, trim marks and press marks (color bars,…).
- Using an MIS system, a customer service rep can create a quote for a customer. During this process a lot of parameters are defined: size of pages, number of pages, size of press sheet, which press and folding machine will be used,… This leaves the MIS system with enough information for a basic description of the imposition. In JDF there is a mechanism called Stripping for exactly such situations. Using JDF stripping, an MIS system can provide a prepress system with a rough description of the press sheet geometry. It is up to the prepress system and/or prepress operator to refine these data and add any data that are missing such as color bars, creep/shingling,…
- The third way in which an imposition can be defined is a fairly static one: a printing company can have a fixed library of imposition templates which cover all of the repetitive jobs that they do. They may often print business cards (85×55 mm) on SRA2 size paper (640×450 mm) and have a fixed template called ‘bc_sra2′ to do such jobs. If the company has a web-to-print portal which is JDF enabled, that system can send a JDF to the prepress system, telling it to use the’bc_sra2’ template for the job.
- Color separation
In a JDF file, color definitions are stored in the ColorPool. As can be expected, spot colors can be defined and it is possible to map one color to another (e.g. I want ‘Pantone 254’ and ‘logo’ on a single plate. An obvious limitation of JDF is that it defines the color intent, an definition of how a job is supposed to be processed. It is up to the unlimited imagination of a designer to add tons of color definitions and weird ways of making use of them to a file 🙂
A JDF file can contain a definition of the screening intent. This information is often not included in JDF because most shops don’t charge customers on the basis of the screening that is used. This means that a lot of MIS systems don’t allow the sales rep to specify the screen ruling. A work-around that is sometimes used is to link the paper selection to the screen ruling, since the choice of paper does influence the screening. This work-around is implemented in either the MIS JDF module or the prepress JDF import routine.
Proofing is one of those areas in which both JDF and the JDF implementation in many systems still needs some refinement. Since prepress is seen as a fixed cost by many printers, there are MIS systems on the market that don’t allow the users to specify the type of proofing that is needed. This obviously means that this information also cannot be embedded in a JDF file.Information that is needed but that may not be definable includes:
- Color proof or content proof
- Page proof or imposition proof
- Soft proof or hard copy proof
- All pages or only a specific range
- Which proofing device is to be used