Wednesday, 26 October 2011

WIDFP? - Printers Marks/Bleed

Printer marks are symbols that appear outside the print area of a document. The marks are used to align separation films for producing proofs, trim the page to its final size and correctly calibrate ink density. (link)



About printer’s marks
When you prepare artwork for printing, a number of marks are needed for the printer device to register the artwork elements precisely and verify correct color. You can add the following kinds of printer’s marks to your artwork:

Trim Marks Fine (hairline) horizontal and vertical rules that define where the page should be trimmed. Trim marks can also help register (align) one color separation to another.
Registration Marks Small targets outside the page area for aligning the different separations in a color document.
Color Bars Small squares of color representing the CMYK inks and tints of gray (in 10% increments). Your service provider uses these marks to adjust ink density on the printing press.
Page Information Labels the film with the name of the file, the time and date of printout, the line screen used, the screen angle for the separation, and the color of each particular plate. These labels appear at the tops of the images.


A. Star target (not optional) B. Registration mark C. Page information D. Trim marks E. Color bar F. Tint bar (link)

Purpose
When printing an image that has more than one color, depending on the method of printing, it is necessary to print the image one separate time for each separate color. Each one is called a "color run," and they can be pulled from the same surface, inked differently, or from a completely different surface. So that the final image is consistent, and so each of the colors lines up correctly, a system of registration is necessary. Different printing devices have different methods of creating separate color runs. (link)



Types of lithography registration
There are many different styles of registration for many different types of printing. These deal with stone lithography, as used in fine arts printmaking.


T-bar
This method, using small measured registration marks on both the stone and the paper, is very accurate and simple to do. The printer measures the exact size of the paper and the desired margins. Then marks are made at both ends of the sheet of paper, and corresponding marks (usually in the shape of a "T") are made on the stone. Then the printer matches the marks on the paper to those on the stone. This way many runs of different colors can be pulled exactly in line with one another, each of them measured from the same system of marks.
Pin-hole
This method involves laying the paper on the un-inked surface, and making a pin-hole through both the bottom and top of the paper, being careful to make a mark in the stone's surface. Then the locations of the holes are transferred to each sheet of paper to be printed. When printing, one should place pins in each hole of a sheet of paper, and lower it onto the inked stone, placing each pin in its respective hole in the stone. This method can ruin paper by creating holes. And if the holes get too large, they lose their function as registration devices.
Eye-balling
This method relies solely on hand-eye coordination. The printer places the paper over the stone-image, measuring and judging registration by eye. This is not very consistent, depending on the person. (link)



About bleed
Bleed is the amount of artwork that falls outside ofthe printing bounding box, or outside the crop area and trim marks.You can include bleed in your artwork as a margin of error—to ensure that the ink is still printed to the edge of thepage after the page is trimmed or that an image can be stripped into a keyline in a document. Once you create theartwork that extends into the bleed, youcan use Illustrator to specify the extent of thebleed. Increasing the bleedmakes Illustrator print more of the artwork that is located beyond the trim marks. The trim marks still define the samesize printing bounding box, however.The size of the bleed you use depends on its purpose. A press bleed (that is, an image that bleeds off the edge of theprinted sheet) should be at least 18 points. If the bleed is to ensure that an image fits a keyline, it needs to be no morethan 2 or 3 points. Your print shop can advise you on the size of the bleed necessary for your particular job. (link)

What is bleed?
If any element on your document layout makes contact with the document border you will have to use bleed. The trick is to place the element so that it goes over border where the document will be cropped after printing.

The term bleed is used for all objects overlapping the border off your document. Let's say you're working on a brochure with images against the sides of your pages. You'll supply the printer with a document somewhat larger then the final document will be.

After the brochure is printed it will be cropped to its correct size. The bleed in your document gives the cropping some room for error. The paper itself can expand or contract, the cropping machine could be setup wrong or the person working on the brochure could make a mistake. There are a lot of factors that could go wrong with the cropping, if you weren't using bleed the images wouldn't be neatly aligned with the side of your printed document.


Two kinds of bleed
A bleed can be a full bleed or partial bleed. With a full bleed you have objects running of your document on all sides. With a partial bleed you'll have a couple of elements running off the document. (link)



Crop marks
For every job you send to the printer you need to place cropmarks on your document. Every industry-standard program on the market will do this automatically (although there will be a few exeptions when you'll have to make them by hand). How far the crop marks should be from the document border is something you should discuss with your printer. For most jobs 3 to 6 mm is fine.

In normal usage you won't see the cropmarks untill you open the exported file, pdf for example. (link)


Marks
At Printing Brain, we’re always looking to demystify print. So today, we look at 3 elements that are often confusing to anyone outside of printing companies but are essential to understand – the colour bar, trim marks and registration marks.


Registration Marks
The little circle with a cross through it is printed using every colour of the four-colour printing process. If they’re being printed accurately, they should overlap precisely so the mark looks entirely black. Therefore if any of the colours are slightly offset (out of register) then they’ll be displayed, showing the job isn’t being printed correctly.

Trim Marks
These are small lines which show exactly where the finished page will be cut during the finishing process. They should display at the edge of each margin.

Colour Bars
Colour bars are printed outside the trim area and are used for quality control purposes by the printer. Squares of colour are printed on the area of the page to be trimmed off, which the printing press operator uses to check colour density and consistency is maintained. This checking process is automated by some printers, with digital scanners tracking the colour bars to ensure quality and consistency is maintained. See also our 5 step guide to Pantone Colours. (link)


Production Tips & Tricks


Crop and bleed marks, those are the straight lines at the corners of your piece. The outer mark indicates bleed, we typically ask for an 1/8th of an inch. The inner mark is the trim mark, this is where the cutter operator will cut your piece. The bleed area is put there to extend any color that is supposed to be all the way to the edge of your piece, so when they cut it out, if the cut is off slightly you won’t have a white border where you don’t want one.

Register marks, a register mark is used for alignment, they are typically centered one on each side of your piece. Since we use multiple colors (cyan, magenta, yellow and black) to make all the colors of the spectrum we have to make sure the four color plates line up (I will explain this in the next paragraph). We use the register marks to register the colors. Each plate on the press has these marks and when they line up all you see is black. If they are out of register the different colors start to peek out from under the black. We then can see which color needs to be re-registered.

Why? If you look at most printed pieces (color copiers work differently and pictures illustrate this the best) with a magnifying glass, you will see that the solid color you perceive is actually made up of dots. There are clusters of four dots called rosettes. By varying the size of the dots in each rosette we can create different colors. A blue rosette would have a 100% Cyan dot, a 50% Magenta dot, maybe a 5% yellow dot and finally a 10% black dot. If you put a bunch of blue rosettes together you get a big blue area in your photo. Now if the plates are out of register, the rosettes might start overlapping which creates what we call a moirĂ© pattern. Which can make the picture hard to look at or the text hard to read or can make colors we weren’t expecting.

Color bars, these are placed on a press sheet so we can make sure the colors are the correct density. By checking the blocks of color in the bar we can make sure the press is placing the proper amount of ink on the paper to accurately reproduce the colors.

Caution, really technical stuff to follow: A color bar usually contains a block at 100%, 50%, and 25 or 35% for each color cyan, magenta, yellow and black. The color blocks repeat across the top of the press sheet. The reason they repeat is so we can check that the color is consistent across the entire sheet (Why? Read the following paragraph on presses). Not all color bars are the same, we use a G7 color bar. The G7 methodology requires us to measure certain percentages and mixes of color for balance and density. So we have a unique color bar to do that. If all of the color blocks read correctly, in theory, the color should then be correct for the printed piece.

How presses produce color: We repeat the color bars across the leading edge of the paper because of how a press operates. A press puts ink on paper using a set of cylinders. In the press the first cylinder picks up the ink, it then transfers that ink to another roller. This smoothes out the color and makes it more consistent across the cylinder. It then transfers that ink to a cylinder that has a press plate wrapped around it. The press plate has ridges on it that pick up the ink off the other roller. Then as the press plate rolls across the paper, it transfers the ink it picked up onto the paper. A press operator can control the ink across the width of the cylinder by adjusting what we call keys. His aim is to get enough ink on the cylinder and to make the ink consistent across that cylinder, which will make the densities right, this must be done for each color, when it is achieved it makes the colors come out correctly in your printed piece. (link)

1 comment:

  1. would any of these registration marks be used in mass productions using flexography? if so which ones and why???

    ReplyDelete