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Prepress & Screen Making




"If it ain’t broke, don’t fix it." This is a popular attitude if you create your own separations. You follow the same steps you’ve always used for producing positives because you learned the hard way about what does and doesn’t work. But it may be time to adjust your thinking. Big changes are on the horizon in terms of separation strategies and production artwork. With more and more companies switching to CTS systems, there will be a push towards smaller dots and additional capability in what level of image resolution we can hold on screen.

"If it ain’t broke, don’t fix it." This is a popular attitude if you create your own separations. You follow the same steps you’ve always used for producing positives because you learned the hard way about what does and doesn’t work. But it may be time to adjust your thinking. Big changes are on the horizon in terms of separation strategies and production artwork. With more and more companies switching to CTS systems, there will be a push towards smaller dots and additional capability in what level of image resolution we can hold on screen. There will be fewer limitations and more possibilities. Even if your shop doesn’t go the CTS route, your competition probably will. The influence of new technology has coincided with a noticeable change in the presentation of printed artwork. You may notice that more and more customers want screen prints to look screen printed, rather than mimic the appearance of another process. What this means is that it is often undesirable for a screen-printed image to have a noticeable dot pattern in a traditional style–dots that change in size depending on the percentage, are arranged at a specific angle and frequency, and have a common shape. Customers want prints that echo the reality of the process used to reproduce the artwork. Designs that use unconventional halftone methods are exciting new options that are relatively easy to create, separate, and print. Some of the popular screening styles right now are etched and woodcut looks, as well as completely random mezzotints. If you take time to practice with new methods of creating halftones, you will be rewarded with a better understanding of the many possibilities at your disposal. And you’ll gain knowledge about how to give an image a custom appearance in the art/design stage, as well as in production. In some cases, you may decide to throw out or adjust your old methods permanently, because what you learned gives you better results and more control over the look of the finished product. Halftone evolution Before we dive into custom halftones, let’s make sure we have a good understanding of the basics. The function of any halftone is to take a grayscale image and flatten it through a screen to form a black and white copy that creates the illusion of gray values through the use of dot patterns. Those of you with a little more history in the business will remember how we used to create this effect with a Photostat camera. The gray information was converted to black dots of varying size and shape, depending on the value of the original image when it was shot through the screen. Now, with Photoshop, converting a grayscale image to a bitmap screen is a snap. Photoshop allows you to produce screens in non-standard ways and use different methods to recreate grayscale images. You just have to know what look you want and test your approach to screening so that you can achieve consistent results. I’ll demonstrate this concept by using two grayscale images. I’ll convert them into a variety of unconventional bitmaps to illustrate some exciting new ways of creating grayscale values that work well with screen printing and, in many cases, reinforce the visual appeal of screen printing more than a standard halftone would. The major difference between different types of halftones is how they are organized. Halftone patterns can have either a variance in distance with dot elements of equal size, such as in an indexed pattern (commonly known as diffusion dither screening), or dots that are spaced equally and change in size, as in a traditional halftone (Figure 1). There also are random patterns that you can use to form other types of halftones. For purposes of identification, I will designate three different styles, which I’ll call sized halftones, density halftones, and custom halftones. Sized halftones Traditional halftones have equally spaced dots that change in size. This form of halftone has stood the test of time and is used to produce gray or color values with subtle gradations necessary for photographic reproduction. It still is the most used halftone for process-color printing. For our purposes, the traditional halftone features elliptical dots set at an angle between greater than 0° and less than 45°. Angles other than 0° and 45° are used because screen mesh, the garment weave, or other printed halftones can interfere with this halftone pattern and create moiré. To avoid moiré from mesh interference, it is a good idea to test a traditional halftone to find the best line count (lines/in.) and angle to prevent destructive patterns from emerging in the print. Density halftones The index dot is the most popular of what I describe as the density halftone. Separations that use index dot patterns are very popular among screen printers, because they solve several problems at the same time. Since the index dot pattern is essentially random, there is far less chance of the screen mesh generating moiré–unless the frequency of the mesh and the dot count of the index are really close, in which case you will still see some pattern interference. When it comes to index dots, if you can hold one dot, you can hold them all and not worry about losing tonal range in your prints. Index dots are square in shape, and they stack right next to each other well. As a result, index dots are good for recreating small type and details (Figure 2). In some cases, the index dots do a better job–and are more consistent–than traditional halftone patterns, which consistently lead to holes throughout the print and lower image-edge quality. However, there are some drawbacks to index halftones. Probably the worst disadvantage is not in the pattern itself, but in the nature of the separation method. To achieve a true index print, where the colors stack right against one another in perfect coverage, a separation set will often need three to six more colors than would a traditional halftone. Another disadvantage to index-pattern dots is that they don’t recreate subtle gradations as well as traditional halftones and tend to have a grainy appearance since all of the dots are the same size. Despite these problems, I know several garment printers who have switched all of their printing over to index dots from traditional halftones because they consistently have better results. The mezzotint is a great alternative to the index dot. Mezzotints in Photoshop are similar to diffusion dither screens, except that the dots are even more random in shape and appearance. If you look closely at a mezzotint, you will see that the dots look like little lakes in interlocking shapes. The mezzotint is useful for more artistic single-color halftones, but its dots don’t stack up as well as the index-color screens–you may see clumping in areas if you overlap several mezzotints. The mezzotint is a popular look with the old-style graphics that currently are sweeping back into the market, and it is a breeze to print for single-color applications. Custom halftones I will now use my example images for the experimental stage of halftone creation to demonstrate some simple methods of creating custom halftone patterns. There are three types of custom halftones I’ve been using lately: line halftones, combination dither/woodcut halftones, and some halftones generated by really cool plug-ins from Andromeda Software. The successful use of these styles really depends on the image. That means you need to start with an image that is of good quality and has a complete range of gray tones. If you have an image that is too dark or washed out to begin with, then the results you get will be far from acceptable. Remember this when you create a custom halftone: The results are meant to be artistic in nature. Again, the reason traditional halftones have been around for so long is that they are very good at creating the illusion of grayscale. Anything that we come up with on a quick test is likely to have lesser-quality results in representing a tonal range. For this reason, don’t be too nitpicky when judging the final result. Another issue is the way that the computer displays images. When you have an indexed image that is composed of square dots, the computer will not display this image very well at most resolutions (best at 100% or 1:1 ratio). The same goes for designs that sport a custom halftone. The display resolution can make your design look very rough, or even distorted, due to the way the computer averages the pieces of the halftone. It will take you some time to build up faith about what the final product will look like. If you absolutely have to know what you will get, I recommend running a quick print on regular paper. Line halftones Line halftones are regaining popularity. You can see line halftones on many major ad campaigns, such as McDonald’s bags. The line halftone imitates an old etching style with a slightly modern flare. To produce a line halftone effect, open your original image in Photoshop and convert it to grayscale mode, actual size, and at least 300 dpi. I recommend 600 dpi if the image isn’t too big. The resolution needs to be high enough so that you won’t see any jaggedness in the lines once you convert them. Next you will want to boost the contrast slightly for most images. You can do this by opening the Curves menu and pushing the white and black points toward each other slightly. Watch the image carefully as you do this to ensure that you don’t over-correct and lose detail in the shadows or highlight areas. Save your design with a unique name, copy the bottom image layer, select all on it (Crtl A on PCs, Cmd A on Macs), and then copy it (Ctrl/Cmd C). This action will copy your image to the clipboard. You can now create a new image this size by using the >File>New command (Ctrl/Cmd N). You then paste (Ctrl/Cmd V) the image from the clipboard into this document and flatten it (Ctrl/Cmd+Shift E). Next, you will duplicate this image and convert the duplicate to a bitmap (>Image>Mode>Bitmap). Keep the resolution the same as the original so you can place this image back into the gray-scale original as a layer of equal size. Select "halftone screen" in the method area of the dialog box. Hit OK and you will then have the halftone-screen dialog come up. Select a rather low frequency to exaggerate the effect (10-20 lines/in. is good) and use a 22° angle with a shape of "line" selected. When this image is finished, select all on it (Ctrl/Cmd A) and then copy it and paste it back into the original grayscale image. Now copy the original grayscale a-gain and create several other line screens that are set at different angles and different frequencies, then paste these back in-to the original document as well. At this point, you can select different parts of these image layers and multiply and/or erase them to create a custom halftone with a variety of lines, angles, and frequencies that emulate an etched look (Figure 3). Dither/woodcut halftones This style of custom halftones gives garment designs an art nouveau look by infusing a wood grain and a rough texture in the image. In terms of size, resolution, etc., you will follow an approach similar to that used to create a line halftone when you prepare your image. Then, when you duplicate the original grayscale image, select it, and copy it to the clipboard, you can create a new document of the same size. Now you have to find a quality shot of a wood texture you can use. Many programs come with textured backgrounds that will work, or you can shoot a picture of a wood grain with a digital camera. This is always a great way to get a quick texture that no one else has, so I decided to go this route with my example (I photographed the wood texture of my office door). I imported this picture and converted it to grayscale, then copied it and pasted it into the blank document that I created from my original image. I sized it using the transform command (Ctrl/Cmd T) so that the texture fit the full size of the image. I adjusted the contrast slightly using the Curves menu so that the image would have more medium grays and less black or white. You do this by sliding the black and white points towards the center of the curve while still on the edges of the curve box (Figure 4). Creating more medium grays will give you a better custom pattern that will display more detail when you push a grayscale image through it. As a final step, I used the sharpen filter twice to define the grain in the image. I then selected all on the wood grain and used the define pattern command (>Edit>Define Pattern) to create a pattern out of my image. Had I not used this pattern at 100%, then it would have created ugly tile lines in the conversion. Now that the wood grain is prepared, I’m ready to compose my image. I make a copy of my original image, convert it into a bitmap (>Image>Mode> Bitmap), and then select the "custom pattern option" under Method. Next, I find the wood-grain pattern that I created, select it, and convert it to a bitmap. Wood, marble, and a variety of other textures can be used in this way to give your designs an unconventional appearance. Some of the best effects are ones in which the texture is a recognizable one that contrasts with the image and pushes it away from the viewer or creates a curtain look. In the example, I created two other layers of dither dots and a mezzotint using the Photoshop mezzotint filter on a copy of the original image. I then used layer-blending options to merge the highlights and shadows together (Figure 5). For a true halftone conversion, I would flatten everything and then convert it again to a dither halftone for creating a positive. However, keeping each component on its own layer gives you the most editing options and is advisable if you have a lot going on with textures. Plug-in-generated halftones If you have a continual need for custom halftones, you should seriously consider obtaining some of the filters from Andromeda Software. They plug into Photoshop and create a variety of uncommon halftone patterns without requiring all of the testing and extra steps associated with generating custom halftones in Photoshop. I found the plug-ins to be simple to use and well suited for creating some great effects. I used the Series 3 Screens filter to quickly create some etching looks and some mezzotints that were way better than what the built-in Photoshop filter could produce (Figure 6). Andromeda’s Cutline filter can do a great composite of effects using selections from an original–similar to what I demonstrated in the line halftone section–but with a wider variety of an-gular and sweeping lines. Think of the etching lines following the shapes of the surfaces in your image. For a more modern twist, Andromeda’s brushed-metal filter (Etchtone) can create some special effects on text and images–also as a bitmap. These are a great alternative to creating your own custom patterns. All of these filters are available online at Casting out conventional halftones You will achieve the best results with any of these alternative halftone methods if you practice with them and test to determine what types of images work best with each style. Don’t depend on your imagesetter’s RIP software to create cool halftones. Instead, reap the benefits of developing your own custom screening methods as you prepare your designs for printing! About the author Thomas Trimingham is the art director of Think Ink Screen Printing, Crystal Lake, IL. He has created screen-printing artwork and separations for more than ten years, and his work has won awards in a number of national screen-printing competitions, as well as computer graphics, wildlife illustration, and logo-design contests. Trimingham also engages in freelance illustration, graphic design, and logo design. He can be reached at


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