Crop marks and color bars

Production Tips & Tricks

Have you ever looked at one of our proofs and wondered what all the marks and colors were for? Let us explain them for you.

Color Bars and Crop Marks

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 moiré 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.

All of these pieces help us reproduce a quality piece for you and to make sure the entire run is consistent. If you have questions about any of the marks you see on your proofs, please talk to your salesperson or CSR.

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