Overprint and registration errors
In previous articles, we discussed various topics, including registration errors. Now, we want to talk about specialized solutions for preventing these errors. Due to the limitations of printing presses and the structure of machinery, many issues must be examined and corrected during the design stage. This is where the importance of Prepress becomes more apparent. Remember that some problems cannot be resolved during the printing process, due to the limitations of printing machines and their structure. Therefore, by using a checklist or Preflight, various issues can be corrected during file preparation, and one of these techniques is Overprint.
Overprint is like an invisible insurance policy that protects your print project from costly errors! And you, as a Prepress manager, with a complete understanding of this topic and intelligent use of it in various situations, will certainly achieve excellent print results and control production costs.
The Meaning of Overprint
We want to explain this technique in simple terms for you. Imagine we want to produce a green color, and your desired code is as follows: C:100 | M:0 | Y:100 | K:0. Now, the material enters the machine (assuming the order of the press units is C, M, Y, K) and passes through the first unit, where C:100 is printed on the areas specified in the file. Then, it passes through the M unit and naturally receives no value. The material enters the Y unit and receives Y:100. Interestingly, the print result is green, and this is because the Y color is overprinted on the C color.
Now, we want to explain the topic of Overprint for black. In the example given, we want to place our text in black on our green color code. As we know, for small elements like Text, Stroke, and lines, we do not use Rich Black due to registration errors. If we have registration errors during printing, the print result will certainly not be desirable, and problems like illegibility and reduced quality will occur.
For example, imagine someone intends to buy a pharmaceutical product, and due to registration errors, the text information is unreadable. In today's market, people are much more aware and make more informed purchases than in the past. Therefore, if you want to participate in this market, you must be able to produce suitable output and reduce printing errors.
Based on the above points, placing black text as K=100% and avoiding the use of Rich Black can create better print results. However, this is just the beginning. Because by default, the underlying surface of any color, including black, is white, and to prevent registration errors, we must use a small technique in the software to fill the white space under the text.
Enabling Overprint
In vector programs like Adobe Illustrator, after selecting an object with K:100, open the Attributes panel. One of the most frequently used commands in this panel is the Overprint Fill option, which combines the entire color of an object with its underlying surface. Of course, this option is for when your object's color is black. Black combined with green, due to the density of the black ink, not only fills the white space underneath but also prints darker black, which is highly desirable for print quality.
Overprint Everywhere?!
You might think that to prevent registration errors, every object of every color should be overprinted. This idea is definitely incorrect. Remember that the Overprint technique combines the color of the object at the higher level with the object underneath it. In the case of black, the result was a darker color for the text, but for other colors, the situation is different. For example, if your text color is red and the background is blue, overprinting can turn red into brown. Of course, the white space behind the text is eliminated, but your original color is also lost. Therefore, Overprint is usually used for black objects.
Is Black Always Overprinted?
Let's examine a case together. In the example below, there is a large black area in the design. If I overprint it, it means the space underneath it will be completely filled. This will increase the consumption of black ink because the white space underneath is eliminated and replaced with color, which means increased ink consumption and increased production costs. Another point arises here. Can the printing material handle this volume of ink over this large area? This brings up a topic called Total Ink Coverage, or TIC for short, which is discussed in other articles.
Alternative Techniques
Let's examine a special example. Here, part of the black color is on a white background, and part is on a colored background. After overprinting, a color difference will definitely be visible. Because the underlying surface of the black is white in one area and colored in another. The combination of black with each of these areas can create different shades of darkness and is easily visible. How about, instead of overprinting the entire object, we only overprint a part of it? For example, a thin line? Registration errors do not occur over kilometers; their range is small, and we are looking to eliminate that.
In this example, you can draw a thin line with a thickness of 0.2mm and overprint it. This is called Trapping. In this technique, the underlying surface of the shape remains white, no color mixing occurs, but the registration error in the underlying stroke layers is hidden. Trapping is useful when your object is colored and you don't want to mix its color with the underlying surface due to overprinting. But you also want to hide the registration error during printing with the stroke.
