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How to Properly Prepare Screen Printing Art Files
By Dane Clement, President, Great Dane Graphics
Whether or not you like the design is subjective and dependent on personal taste. But aesthetics aside, your artwork needs to be created and converted into a file format that will work with your designated process.
If the resolution is too low, you haven't properly separated it or saved it into the appropriate format - you are not going to get professional results.
While there are some caveats for each of these processes, in general, art file preparation is broken down into screen printed or digital. For this piece, we will focus on textile screen printing.
Direct screen printing is more labor intensive than digital due to the fact that once the artwork is created, each color must be printed to a film. The film is then put on an exposure unit, which transfers the image to an emulsion-coated screen, or a computer-to-screen (CTS) unit directly images the screen that eliminates the film. The screen must then be washed to remove excess emulsion and then it is ready to be set up on a press.
Because screen printing is so much more labor intensive, it does not make financial sense to use this process for quantities of under 24 pieces. In fact, many shops have a minimum of at least 48. The quantity has to be high enough to amortize the setup costs over the number of pieces being printed.
Screen printing can be divided into two categories: spot color or full (four) color. In this article, we will focus on four-color and simulated process. Although you can use the same artwork for either, the file preparations and separations are different.
Spot color means that each color is separate and independent and prints only in that shade. So if you have a three-color design of red, green and purple, you would need to create a film for each of those three colors and each color would be printed one at a time. A spot color design can be created from a vector or raster artwork file depending on the situation.
The vector format is essentially line art and is easy to edit. The two most popular programs used for commercial apparel decorating to create vector artwork are Adobe Illustrator (using the .ai file extension) and CorelDRAW (.cdr). There are, however, other programs on the market that will create a vector file.
Vector artwork is ideal for logos, text, borders, shapes and even complicated illustrations, in some cases. This format uses a postscript language, so resolution depends on the printer's quality, not the artwork's quality, making it easy to edit and resize without losing resolution (detail and clarity). Another bonus: Decorators can print spot color films directly from vector art as long as they create the art using spot colors with no additional art time.
To reproduce a multicolor design using four-color process, it must be separated into cyan, magenta, yellow and black. The halftone dots, when printed, will help create all the other colors in the design.
The biggest advantage is it allows you to have a multicolor design without using more than four screens, which saves time and money. Now, you may need an extra screen to create a white underbase to print your design on top of and sometimes you will use a spot color to make a color pop more. For this reason, I recommend simulated process over four-color.
Raster artwork is a bitmap file that is created using a series of dots or pixels. Halftone screens are used to reproduce this type of artwork for screen printing.
Common raster bitmap extensions include TIFF, PNG, PSD, EPS, BMP, GIF and JPG, the latter two of which are usually small, low-resolution files made for fast loading on the Internet. They should not be used for garment decoration. The number-one image editing program for raster images is Adobe Photoshop (PSD), although Corel PHOTO-PAINT (CPT) and others are used.
Bitmaps work well for reproducing continuous tone images such as photographs and illustrations. Bitmap images are resolution dependent. Each pixel is assigned a specific color value. It can only be resized if it was originally created with enough resolution, so unlike with a vector image, you must pay close attention to resolution.
For example, if an image has only 72 dots per inch (dpi), when enlarged up to 300 dpi, dots are added to fill in the space between the pixels and this results in a blurry or fuzzy image.
For the purposes of textile screen printing, there are more ways than one to separate colors depending on the look you want or the size of your screen printing press. Here are examples of three popular methods:
File Preparation of Vector Artwork
If you use different opacities of a spot color or use gradients in your design, halftones will be required to reproduce your image.
If you are printing on a dark color, you will need to add a white ink underbase that will go down first and then subsequent colors are printed on top. This is to ensure that your colors remain bright and true.
Underbases are created at different densities depending on what color goes on top. For example, a light, bright color, like yellow, may need a 100% underbase. However, a darker color such as navy should be at a lesser percentage. The higher the percentage of underbase, the thicker the layer of ink, which creates a heavier hand. The goal is to use the least percentage possible, but still get sufficient coverage to allow the color on top to pop.
File Preparation of Raster Artwork
When scanning or photographing original artwork, you have control over the resolution and size.
1. Set your resolution. Go into your settings and choose 300 pixels and 14 by 14 inches to ensure you have sufficient resolution for printing. That will cover any decorated apparel type usage.
What you cannot do is download low resolution artwork from the Internet. It will never be high enough resolution to be used unless you are able to obtain a high resolution version.
2. Separate the artwork. Separations are done by importing the raster artwork into software that can do separations, such as Separation Studio.
Although you can manually create separations in Abobe Photoshop or CorelDRAW PHOTO-PAINT, I do not recommend it. I always use Separation Studio, but there are other programs on the market as well. Once this is done, each color file is sent to the printer to output the film for exposing the screen.
If you use Separation Studio, it automatically saves the file in a DCS 2.0 format, which is what I recommend. If you do not use Separation Studio, then you can save it into this format from Photoshop or Corel PHOTO-PAINT.
Normally, any raster artwork (created in Adobe Photoshop or CorelDRAW PHOTO-PAINT or other raster software program) has to be separated into four process colors or simulated process color prior to printing out the films used to expose each screen.
3. Add type. Once artwork is separated and in your graphics program, you can add type to it and choose what color you want the type to be. You also can size it up or down depending on its location and application.
Once you have the type the way you want it, I recommend saving an original with all your text and layers as a copy for yourself. Then save it as another file, convert the text to outlines and send that to your screen printer or to your production department.
You do not have to convert the type to outlines; however, it helps avoid potential issues. One example is if the person you are sending a design to does not have the font you used installed, it may change the font to something else. Essentially, it ensures the design gets printed exactly as you intended.
4. Create an underbase. If you are printing on a dark color garment, you'll need to add a white underbase screen. If you use Separation Studio, it creates one automatically as part of the process. If using another program, you may need to create one separately.
The goal is to always create a solid enough underbase to ensure you get bright color, but not so solid as to dramatically increase the heaviness of the print. If you print 100% white underbase, it will give it a heavier hand.
5. Send file to film printer. By saving all your colors to a DCS 2.0 or PDF, you only need to send a single file to the printer and it will print out all the colors, underbase, and any additional spot colors as indicated.
Dane Clement is president of Great Dane Graphics, a GroupeSTAHL company. Clement has been speaking and writing for the decorated apparel industry since 1987. He is considered an expert on computer graphics and color separations for textile screen printing, dye sublimation, digital direct- to-garment and heat-applied graphics. He is the author of T-Shirt Artwork Simplified, a how-to book on creating artwork for decoration apparel.
This article appeared in the SGIA Journal Garment Edition, Summer 2017 Issue and is reprinted with permission. Copyright 2017 Specialty Graphic Imaging Association (www.sgia.org). All Rights Reserved.
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