- [Instructor] You have to consider
that applying ink to paper is a physical process.
And as such, there are some limitations.
For example, something called Total Area Coverage or TAC.
You'll sometimes hear it called TIC, Total Ink Coverage.
But there's a limit to how much ink you can pile up
on a piece of paper on a given press.
Now, what do I mean by total area coverage?
How do I measure that?
Well, add up the numbers.
For example, I've given you a value here.
Cyan 100, magenta 50, yellow 20, black five.
You add that all up, it's 175%.
Now, coated papers support a higher total ink coverage.
Uncoated papers because they're absorbent
have to have a lower TAC.
And like I said, this is sometimes referred to as TIC.
So, what happens if you exceed maximum ink limits?
Well, on a sheetfed offset press on coated stock,
your ink limits are around 320 to 340%.
That's pretty generous.
On a heatset web offset press,
which sort of bakes the ink,
if you want to think of it that way on coated stock, 300%,
which is really good for a web press.
On a sheetfed offset press on uncoated stock,
you're limited to between 260 and 280%.
On non-heatset web offset, uncoated stock,
the numbers really go down, 240% or less.
So, what happens if you exceed those maximum ink limits?
Well, you can get muddy color
because of uneven adhesion of inks.
As the inks are laid down,
each ink has to adhere to the previous coat of ink.
And this can delay drawing.
You may experience something called picking
where undried areas of ink pick off during handling.
Let's take a look at an image that has a large black area.
And let's see if this could cause us a problem on press.
I've opened it up in Acrobat and asked Acrobat to show me
what the total area coverage is.
And you can see that encircled there, it's 369%.
And at the bottom I've said, show me areas
that exceed my specified total area coverage of 320%.
So, this is on a good sheetfed press.
And that bright green shows me all of the areas
that are going to exceed that desired ink coverage.
So, what's going to happen?
This is going to cause a problem on press.
Now, little bitty areas that exceed the TAC
are not going to be a problem.
But large areas like this,
these are definitely going to be a problem on press.
So, what can we do about that?
Well, it's good if you examine images
using Photoshop's info panel.
And then you can check using separations preview
in InDesign.
It'll give you some of the same information.
And then as I just showed you,
you can use something called output preview in Acrobat.
So how do you fix it?
Well, if necessary, you can convert it to RGB in Photoshop
and then reconvert it to CMYK.
So let me show you what I did with this image.
On the left, you see the four printing plates,
cyan, magenta, yellow, and black.
And on the right,
you see a reconverted version of the image.
So, looking from left to right,
start at the upper left hand corner
and you can see how dark that area
is behind the book in the cyan.
Look at the equivalent area in the cyan on the right.
You see how much lighter it is.
The same for the magenta.
It's much lighter in the area on the right.
The yellow is lighter as well.
And the black is still solid.
But if you look at the lower right of each set of images,
you can see how the values have changed.
369% total ink coverage on the left, 300% on the right.
The image on the right
is going to print with no problems on press.
Here's something else to consider, registration.
Now, registration isn't something that you can control.
But it's something that can happen on press,
if there are problems with press alignment.
Now, keep in mind that presses are highly computerized now.
They are self-monitoring.
You very rarely see misalignment on a press.
But this is what it is.
As the inks are laid down color by color on paper,
that alignment of colors is critical,
if you're going to preserve detail.
And preserving that detail is called registration.
So, if they're not correctly aligned,
well, this is called misregistration.
Now, I'm talking here about offset presses.
On digital presses, the colors are laid down simultaneously.
So there's less likelihood of misregistration.
And again, presses are so controlled now
that the likelihood of registration is very slim.
But let's talk about the issue.
If you look at the image on the left,
everything's nice and sharp.
Look at the image on the right
and I think you can see sort of a rainbowing effect,
a haloing effect.
I'm going to enlarge that so you can see it in more detail.
And again, this is very exaggerated.
The chances of this happening on your print job
are exceedingly small.
So, just know that registration is important.
You know, that the presses are very well controlled.
But this is what misregistration can look like.
You might've seen it in your Sunday comics
in your newspaper.
The reality, as far as registration on presses is concerned,
is that the presses are highly computerized.
Both digital and offset presses are very high precision.
So, misregistration is rare.
Trapping compensates for tiny irregularities
in registration.
So, what is trapping?
That's where dissimilar colors meet.
And you have to make a bit of compensation.
If adjacent color areas don't share an ink in common,
for example, if you have a yellow area next to a cyan area
and there is no ink in common,
any misregistration would result in little white gaps.
So, what do you do?
Create thin little rims consisting of both colors.
And I mean very thin, 0.003s of an inch, 0.07 millimeter.
Now, commercial printers have sophisticated software
to do this.
You should never be asked to provide trapped files
for print.
So, let me give you sort of an exaggerated example
of what trapping is.
Here is an ideally printed piece.
There's no gap.
But what if there's some misregistration?
And again, it's never going to happen to your job,
not this wide.
But this is an exaggeration
to give you an idea of what could happen.
These are two spot colors.
A spot orange and a spot blue.
They have no color in common.
So, what happens is that the printer creates traps.
And you can see the little dark lines around.
And again, I'm exaggerating.
Trap lines are not that thick and they're not that dark.
You'd really have to look very, very close
with a magnifying glass to even see trapped lines.
Keep in mind that these issues,
total ink coverage and registration
and trapping are topics handled by the printer.
But on the other hand, the more you know,
the better you'll be able to prepare your files
and ensure that your job prints as expected.