Great Seps are the Start for Great Spot Color Prints

Part 1 of our "How to" guide to creating great manual spot color separations.
November 01, 2006

All good screen printing starts with good screens, and making sharp screens starts with generating good color separations from your original digital image.

More than likely, your shop employs an art department or artist with the ability to create at least simple separations for garment printing. Of course, software is advancing so quickly these days that so-called "push button programs" make it fairly easy for even unschooled staff members (or shop owners) to produce separations. However, if you want to print eye-catching spot color prints, chances are you will face some complex designs that can prove to be too much for these programs.

If you are fortunate, you also have a staff or freelance artist/designer who can tackle very difficult images and translate them to excellent separations. If you want to speak the same language as that artist or begin to produce top-quality seps yourself, then you need to get familiar with applying some fairly sophisticated techniques in your image-editing software. (One note before we get too far along, while I work in Adobe Photoshop, all the principles in these articles can be applied in CorelDraw using, obviously, a slightly different set of commands and keyboard shortcuts.)

In this series of articles, we will explore manually created spot color separations from A to Z, from artwork preparation to advanced techniques for printing on dark garments, and give you a variety of tips for tackling any challenges that come your way.

GOOD SEPS START WITH GOOD ART

It's impossible to produce good spot color separations when you start with poor quality artwork or image files in the wrong format. This means you should educate clients on the best, simplest and fastest methods to create artwork intended for manual spot color separation and printing.

Artwork should be in digital image files (whether photographs, composites or graphic illustrations) created at 300 dpi resolution then saved (or downsampled) at no less than 150 dpi at the final print size.

If a client brings you an image file that's 150 dpi at about 5 inches across (print size), and asks you to print it at 12 inches across the front of a shirt, you have to explain that it's impossible to produce a crisp, quality full-front print from a file that small. To even attempt this, you would have to enlarge the image more than 200 percent, which will drop the resolution to about 75 dpi. The image will still look swell on the computer screen, but even a simple inkjet or laser hard copy will reveal the well-known "jaggies" or pixilation that indicate image resolution is considerably below the minimum of 150. Enlarging or upsampling any digital image is tricky business, and a blurry or pixelated image is almost always the result.

On the other hand, downsampling, or decreasing image resolution from 300 dpi to 150 dpi, is desirable. It will cut the file size in half, making it much easier and faster to work with, yet not compromise its final print quality.

Working with smaller image files—that still have high-enough resolution—is a good practice, especially for folks who don't have new, high-end graphics-oriented computer systems. The latest workstations have dual processors and ship with at least 1 GB (gigabyte) of RAM (random access memory). If you work on a modestly priced computer system that is even just two years old, it's likely to have a single, slower processor and probably came with 512Megs of RAM (that's / a gigabyte) or perhaps as little as 256Meg (/ GB). Extra RAM is fairly inexpensive these days and, especially for Windows machines, is available off the shelf at the local computer store. It's easy to install, and I highly recommend that you max out the RAM in your machine if you are going to use it to create separations.

KEEP YOUR LAYERS

Back to our artwork—if your client brings you an image file created and saved in more than one Layer, it is crucial that you preserve those Layers. Never flatten artwork (Layers > Flatten Image) or merge a Layer onto its Background (Layers > Merge Layers). It is much easier to manually separate a piece of artwork that remains layered. One Layer at a time can be turned on, or selected, while others are turned off (see Figure 1).

Working in Layers allows easier creation of areas and requires less erasing or manual removal in your Channels. (We'll get into this in more detail later in the series.)

An artist should, however, limit the number of Layers in an image file to, again, make the file size more manageable and easier to work with. Be sure not to combine Layers that include artwork that rests over the top of one another. Similarly, very complex parts of the image should remain on their own Layer. For example, an artist might create a Photoshop file with several dozen Layers. It is much easier to separate that image if you reduce it to 10 Layers from, say, 25 Layers or more. If there are pieces of art that do not touch, or there are areas that can be combined onto one Layer without affecting the artwork, it is best to do so.

The color mode used to create the image can be either RGB or CMYK, yet most of this particular separation process will be done with images in CMYK mode. Always keep in mind how out-of-gamut colors (see "In and Out of Gamut" on page 47) can be affected when switching a design from RGB to CMYK (Image > Mode…). Although it typically does not affect how colors are broken down for separation, it can make diagnosing color breaks more difficult as well as negatively affect the look of the design on screen.

TUNING INTO CHANNELS

Before beginning, you may wish to either have a color copy of the image at your workstation or split your screen so you can continually compare the original image to the working file. This on-screen sample can be flattened and saved as a compressed JPEG file, since you're only using it for color proofing.

In Photoshop, separations are created in Channels. The process can be looked at in this way: Layers are used to build a design, and Channels are used to break that image into useable color screens for reproduction. However, both Channels and Layers play significant roles throughout the spot color separation process. You can use Layers to make decisions and selections that produce color Channels that will, in turn, create separations that eventually prove much easier to print, and give better results. Keeping this in mind, we will begin with the easiest colors to identify and create while both our Layers and Channels palettes are open.

ALPHA CHANNELS

Open your Channels palette. Depending upon the image mode, you will see either the RGB or CMYK source channels that, when all turned on together, represent the color image or design you're working on. You can easily create a new channel by clicking the Create New Channel tab at the bottom of the Channels palette (third from left, next to the trash can). You can also duplicate a Channel by click-dragging it down and dropping it onto the same tab.

The fly-out menu also provides these choices. (All Photoshop palettes have these fly-out menus. You access them by clicking the black triangle inside the silver button in the top right corner of the palette.) Using either method, create a new Channel and a dialog box will appear showing the new Channel's name, Alpha 1. Click OK.

Each color of your spot color design will be an Alpha Channel and rest beneath the Source Channels above.

GARMENT COLOR CHANNEL

Before beginning to separate ink colors, create a new Channel and label it Garment Color.

This Channel will reside directly under your Source channels (CMYK or RGB). Select all (Apple-A/Ctrl-A or, from the top menu bar, Select > All) and fill this Channel with 100% black. Now double-click on the Alpha1 icon in the Channels palette to pull up the Spot Channel Options dialog box. At bottom left is a color selection box. Double-click to open the Color Picker dialog box and select a color that closely resembles the color of the garment on which you will print this design. Make sure Solidity is set at 100% and click OK (or hit Enter or Return on your keyboard).

Viewing the Garment Color Channel by itself will appear as a solid black page. However, as spot color Channels are created and viewed, this Channel will appear in the color chosen to represent the shirt. This is a great way to preview separations and designs to visualize how they will actually print on colored garments. You should always do this when the design is printing on any garment color other than white. In the case of a white garment, this step is not necessary, as viewing several channels together defaults to a white backdrop.

BEGINNING THE SEPARATION PROCESS

As preface to manually outputting spot color from a digital image file, you are always well advised to remember there are several means to an end in the separation process. No two artists use exactly the same methods to produce reliable sets of separations, and this theory should be embraced.

An excellent separator may use several different methods; including taking advantage of push-button programs to get a head start. To fully understand how to find and achieve different tones from a design or photo takes practice, and no method should be discouraged. As this series progresses, I will present the method I am most comfortable with and explore other means to the same end...a great set of separations.