What is the term knock out in Graphics

[Brijithkumar@adobeforums.com]

Iam constantly coming to the term "Knockout" in various graphics user forums, but dont have any idea what it is. Can anyone of you explain it what the term means?

[Kurt_Gold@adobeforums.com]

Brijith,

it's what happened to Klitschko last week…
or maybe this?
-> <http://www.corel.com/servlet/Satellite?pagename=Corel2/Products/Home&pid=1047022702205>

Kurt Gold

[lee_vickers@adobeforums.com]

Say you have red text on a black background which is to be printed. To get red printed over black, the black area 'behind' the text must be 'knocked-out', or 'empty', to allow the red to sit amongst the black (otherwise the red will not show up over black ink).

This is a simple explanation in an ideal world; The chances of both plates matching perfectly (and the text and background keying together) are slim so you would also use 'Trapping' to prevent the paper-white showing through the gaps. Trapping extends one or more colours to overlap other colours to cover that gap.

Have a really close look at a glossy mag under a bright light and you can see colours being trapped and knock-out, usually with blocks of colour. Just make sure it's not a lad's mag in case your girlfriend catches you.

Lee

[Gary_Newman@adobeforums.com]

This happens with the much more common black type on any lighter color, too. A "hole" appears under the type, through all the other plates, so the black ink can print directly onto the white paper. In this case, we can tell the black type to overprint instead of knock out, in which case the black prints onto the ink of the underlying colors.

[lee_vickers@adobeforums.com]

Quite right, Gary.

It is a can of worms though!

Lee

[jonf@adobeforums.com]

But if you're seeing it in "users forums" it may not always be being used correctly. I've seen people improperly use the term knockout to describe a mask, or the punchout or "hole" in a compound object, for instance.

[Wade_Zimmerman@adobeforums.com]

Jon though the term is often misused as you describe because of the way it is created in the digital world I think it is understandable how it can get mixed up.

I think if one was doing the mechanical art with paper it would be easier to understand.

[hitpawz@adobeforums.com]

To be honest, I've never had trapping or knock out come up in my work. I know what it is, but I've never worried about it. I've proofed hundreds of print jobs and have never once noticed a problem. I've never had a complaint of it either. Am I alone?

I don't want to be the client that the printers hate, so I ax:

Who deals with knock outs? Printer or designer? How can the designer make that easier?

Are there any circumstances where it's imperitive that you trap?

Are there any where you absolutely should not trap? (Where trapping something will ruin the piece) (eg. pink over blue? yellow on blue? white on rice?)

I'm starting to think that maybe people simply haven't caught it or didn't bother telling me I screwed the pooch. I have seen examples of trapping problems, but never in my outputs and I'm getting self-conscious about it.

[Dee Holmes]

Usually the printer's prepress department does the trapping. The printers know how much movement to expect on different presses.

[hitpawz@adobeforums.com]

So they DO hate me!

[jonf@adobeforums.com]

The most common knockout problem I see is when black (usually headline text) is printed over a background which is part white, and part color. You should overprint with a rich black (which contains percentages of cmy as well as 100% k) in these situations, or knock it out of the background color. If not, there is a noticeable difference in the black where it prints over the color, and you'll see the edges of the background color area showing up through the black.

I've also accidently had colors overprint that should have knocked out. When I create a new object in AI it picks up the Attributes of the most recent object I had selected. So if I had just been working with black text that was set to overprint, and then create a new object in some other color, and set it over an area of color, it defaults to overprint. If I forget to check it and change this I get a color at press which overprints the two colors rather than knocking out and trapping. Embarassing. Normally I've caught this at proofing, but I wish it wouldn't happen.

In most cases the printer's software can handle the trap more efficiently than you can, but some glaring errors can sneak by.

[hitpawz@adobeforums.com]

Overprinting is another thing I've never dealt with even though I know exactly what it means.

Are there any obvious situations where I should implement it? From your context, I assume black type over color.

1. Is that just large, such as headline, text only or should all bodies of black text overprint?

2. Is that another standard thing that the printer will go in and adjust?

3. Is there a difference between overprinting 100% black text and just setting the black to include all the 4 colors?

4. This is something that I've done in practice and am starting to think is a huge mistake. When I want a rich black, I just pop that baby to 100,100,100,100. What are the drawbacks to doing that? I've done it for as long as I've been a designer and have never heard anyone tell me it's bad practice. Is it?

[John_Slate@adobeforums.com]

The most common knockout problem I see is when black (usually headline
text) is printed over a background which is part white, and part color.
You should overprint with a rich black (which contains percentages of
cmy as well as 100% k) in these situations, or knock it out of the background
color. If not, there is a noticeable difference in the black where it
prints over the color, and you'll see the edges of the background color
area showing up through the black.




Actually this would be an overprint problem.

Overprinting black, which is the default of most programs and rips is a tricky subject, due to the fact that 100% black ink is by no means opaque, and if the black area is big enough, will clearly show variegated tone in C M and Y underneath (actually on top... normal offset sequence is KCMY)

Overprinting is the polar opposite of knocking out.

The rules of postscript overprint are such that any of the 4 color channels in the overlying object that contain 0% will allow the dot percentage in the underlying object to print on that channel.

So 0C/0M/0Y/100K overprinting 0C/50M/50Y/10K will be 0C/50M/50Y/100K.

40C/0M/0Y/100K overprinting 0C/50M/50Y/10K will be 40C/50M/50Y/100K.

See? Wherever a zero is, the underlying number comes through.

But 1C/1M/1Y/100K will not overprint 0C/50M/50Y/10K because there are no zeros to allow the underlying object to come through, so the top object will remain 1C/1M/1Y/100K.

Setting things to overprint, that should not be set to overprint, used to be a problem in the pre-overprint-preview days, since applying the command did not change the preview at all, and you had people inadvertantly setting white to overprint, which in many workflows makes the white dissappear:

So 0C/0M/0Y/0K type overprinting 0C/50M/50Y/10K will be
0C/50M/50Y/10K, or the same color as the background... bye bye type.

Or setting cyan to overprint yellow makes green, but only if you have overprint preview on.

So knocking-out then would mean that even 0% in a channel of an element set to knock out will "make a hole" in that channel of the underlying object.

By default all colored objects, except for black (and in QXP over 85% K), will and should knock-out.

Generally speaking, if you are dealing with higher end suppliers, all issues of overprinting vs knocking out, and ESPECIALLY TRAPPING, should be handled by the supplier.

And as a rule, unless you know what you are doing, don't go setting things to overprint, and let program defaults make those decisions.

Though be wary of Illustrator that knocks out 100k fills by default (the overprint black filter is handy for this)... but generally that is not an issue since:

Many rips and workflows may be configured to totally ignore all of your overprint commands and also may be set to overprint all 100K objects, even if you go to the trouble of setting them to knock-out.

And high end rips often include trapping software in a composite workflow where all the trapping that you have set is also ignored.

[John_Slate@adobeforums.com]

One other thought on overprinting.

Sometimes it is really what you want to do, like setting spot colors to overprint in Illy, since there is no mixed inks. (OK you could use multiply instead but you might also use overprint)

If you do set colors to overprint each other, you might want to flag that to your supplier, because if they aren't paying close enough attention, their rip may ignore the overprint.

[Gloria_Chen@adobeforums.com]

Never use 100K, 100C, 100M, 100Y, unless it is for registration marks. Printing presses can't handle 400% of ink on paper. If you need to print a rich black, use 100K, 40C, 30M, 30Y.

[jonf@adobeforums.com]

"Actually this would be an overprint problem."

I know, That's why the post partially quoted actually said:

black (usually headline text) is printed over a background which is part white, and part color. You should overprint with a rich black (which contains percentages of cmy as well as 100% k) in these situations, or knock it out of the background color.

What I meant was that a knockout would have prevented the overlap effect. But I agree, an overprint with a rich black is the better solution since it requires no choke.

Sorry if I stated that imprecisely and led to confusion.

[Dee Holmes]

Depends on what substrate you're printing on.

We print on poly (plastic bags). When using our 6 color CI press we use for process printing, a rich black would be 95C, 95M, 95Y, 100K. It makes a great rich black.

We use 95% because it prints a smoother screen than 100% can print out.

[Wade_Zimmerman@adobeforums.com]

Gloria I have a printing company that does my postcards and they suggest making the rich black 99c 99m 99y 100k. And it looks great!?

8pt. drop out type looks beautiful!

[Doug_Katz@adobeforums.com]

Thanks, John Slate. Very informative for me.

[Gary_Newman@adobeforums.com]

Here's something that used to happen in the old days, that you should still look out for. I would have a photograph as background, with a large headline in white filled type. I wanted the type to have a translucent 50% K drop shadow. I put on offset copy of the type in back of the itself, filled it with 50K and set it to overprint. So, the white type was knocked out of all four color plates. The area of the 50K did not appear on the CM and Y plates, but appeared as a solid 50K on the black plate, overriding any black values in that area of the photo. The lesson is that any color set to overprint will have no effect on its own plate. You might expect a 50K overprint area to combine with an underlying 20K to make 70K - but it doesn't. It makes 50K. And a 20K overprinting 50K gives - 20K.

I don't use overprint much any more, except when small type sits on color. I find it much more effective to use the Multiply blending mode.