One very important process that takes
place in prepress is something called imposition.
So, what's imposition?
Well, it's really just positioning pages for the
location which they're going to print on press.
So, what do I mean by that?
Why is imposition even necessary?
Well you can get an idea of what happens during imposition by taking a magazine,
pulling out the staples, pulling it apart and
looking at how the pages are really printed.
You're going to find
out that page two doesn't print opposite page three.
Imposition is tailored to the trimming and binding processes
that are going to touch the job after it's printed.
And it optimizes the way this job prints based on the press sheet size.
So, that leads us to a discussion of reader spreads versus printer spreads.
The way we read is called reader spreads.
So, for example, in this little eight page brochure, there's page 1, the cover,
by itself, and then 2, 3, 4, 5, 6, 7, and finally page 8, the back cover.
So, this is the way you would design as well, but
this is how the pages might be laid out at the printer.
Eight and one face each other. Two and seven, six and three.
The only pages that print the way we read them
is what we call the center spread, pages four and five.
Now, this is not something you need to do.
This is something that takes place at the printer.
You build in reader spreads,
they take it apart and put it back together in printer spreads.
So, the first part of this involves choosing
a template for the position of the pages.
Here you can see the imposition specialist shopping through the
list of templates and finding the appropriate one for the job.
Now, this is just a layout.
It doesn't have any art work in it.
These are just the locations where the pages are going to be placed.
As you might expect, more complex jobs require
more complex templates.
For example, something like this, a textbook or anything else that has a
high page count and in this case,
is created with something called perfect binding.
Perfect binding is what gives you that flat spine, like on a textbook.
So in a perfect bound book one of the things that
happens is that there needs to be bleed on all four sides.
Now, we're not going deeply into binding here, but the
way this is created, the pages are combined in little
sets called signatures and then those signatures are combined and then
they're glued on the back and then that part is ground off.
That's why they need bleed on the inside where you don't normally supply it.
And again, this is not something that you
do, this is something that happens in prepress.
But if you're creating a high page count book that's going to be perfect
bound, as you can imagine it takes a little time make all this happen.
So, it can add to the job schedule.
Here you can see the
imposition operator has chosen a much more complex template,
and this is for a higher page count job.
You can see some of the page numbers
there, but this isn't necessarily the whole job.
But again it gives you an insight into the way
these pages have to be positioned on a press sheet.
So you notice that some print with a head left, some print head
right, and again it's all about making the most of that sheet of paper.
Remember that RIP means Raster image processor and that RIPping is
a good thing.
So the way imposition is performed, each individual
page of a job is processed, it's RIPped.
And then that RIPped data is what's positioned in those imposition templates.
Here you can see the RIPped artwork in place.
And so this gives you an idea of what's happened up to this point.
Those individual pages have been RIPped, now they've been rolled
into that imposition template so that they're in the correct position.
And when he views it on screen, you can see that
it already looks like the printed job that it's going to become.
But it's a long way from being a printed job at this point.
Because this data is going to be used to image a very expensive printing
plate, it's important to carefully examine that
data before the plate setter is fired up.
Here the imposition operator is taking a closer look at the ripped data.
Notice that you see half tone dots already and
that's because what RIPping does is create a literal
image and that image is used in this case by
the plate setter in order to image each printing plate.
And we're seeing all the colors together there.
You can see the half tone pattern.
And the next step is going to be for him to send this data to the platesetter.
The platesetter is going to burn all the plates required for the job.
Those plates are going to be mounted on press and then the job is going to run.