halftones in printing



When you work with graphics for printing  you  immediately notice that, wherever or however you work on them,  there are more options than you can possibly know all about. There are options in cameras and software to add a color, alter light, alter line, control the printing, to control appearance on screen and a few thousand more just below the surface. It can be more than overwhelming when you are trying to learn something new, but thankfully there are a few basic concepts that occur again and again. Over the next few weeks we will be exploring these options and how they relate to getting an image looking great in print.


Today we will start with a few basic concepts of resolution in print. Namely two words: dots and halftones.


So what is halftone? Or a halftone? And what happened to all the tones, that they were cut in half?


Well halftones are an important part of printing images. If you were to get out a newspaper and look at an image through a magnifying glass you would see that what appears to be a persons face or any object – is in fact a collection of dots. These collected dots laid out in various sizes and at varying distances from one another are what is known as a halftone. That is, a printing process that uses small dots to create an optical effect that appears to be a continuous tone to the human eye. So that a the varying shadows and highlights of human skin for example can be recreated by a printing press. Take a look at the image at the top to see a simulation of a halftone.


This is achieved through black ink, or through the mixing of colored inks in the process printing system we discussed in an earlier post. And the varying spaces or size of these halftones determine how well the final image will print. A fine smooth halftone yields a clear crisp image. A halftone of blurry or choppy dots equals the same effect in the final image.


The dots you hear about when printing are directly related to this halftone. A press prints by spraying or pressing dots onto a page. There are different shapes of dots depending on the kind of machine or the type of printing, but often in offset printing they are shaped like little circles.  The interaction between the dots and paper is where the magic happens for any print, and so it is carefully monitored by your printer.


When dots hit certain papers they either come to a rest on the surface or get sucked right into the fibers of the sheet. How this happens and to what degree determines a lot about the final image. Some papers might create a crisp clear dot, while others create a fuzzy dot. Each has its place and its effect. This is essentially what is called dot gain, and it plays an important part in knowing which papers to choose for a given project.


In fact you can see a similar effect by holding a felt tip pen against a sheet of paper for a few seconds. The ink will leak from the pen, and on some papers you can see how the ink spreads into the paper. This will show you how important it is to control these dots on the press and the importance of having a good pressman to monitor a job.


Of course there is a lot more detail to consider in actually getting an image to press, but luckily if you are working with a good printer, then you won’t have to worry about it – because the printer will. But its always good to know a little bit about it, so when a pressman starts talking you can keep up.


So we are just getting started with images and resolution. We will be back in a few days to build on these 2 concepts and get onto questions of resolution and all those ‘pi’s. That is LPI, PPI, and DPI. So stay tuned.



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