Tuesday, March 01, 2011
How to Create a Digital Underbase for a Direct-to-Garment Printer
Follow these procedures to lay the foundation for great inkjet prints.
The secret to producing the best possible quality dark shirt print with a
digital direct-to-garment printer relies on your ability to create a
good underbase. This ensures the print has a soft hand and the colors
are vibrant. Creating an underbase is not difficult, but most people
don’t know how to do it. They rely on the RIP software that came with
their printer. RIP is an acronym that stands for raster image processor,
and not all RIPs automatically create a good underbase for digital
direct-to-garment printing. This article will show you how to control
your RIP to produce the best prints from your inkjet garment printer.
Once you know which tools to use, it’s pretty simple. For example, if you want to print bright, fire engine red on a dark shirt, you will need a lot of white on your base channel under the red — at a density somewhere between 80 to 100%. However, if you intend to print a darker shade of red, your underbase may need to be only 40% to 50% as dense. You learn from experience where to boost the underbase and how to handle certain colors. I create my underbases exactly the same way 90% of the time; however, with certain colors like reds, you may have to go in and make some adjustments.
Once you know which tools to use, it’s pretty simple. For example, if you want to print bright, fire engine red on a dark shirt, you will need a lot of white on your base channel under the red — at a density somewhere between 80 to 100%. However, if you intend to print a darker shade of red, your underbase may need to be only 40% to 50% as dense. You learn from experience where to boost the underbase and how to handle certain colors. I create my underbases exactly the same way 90% of the time; however, with certain colors like reds, you may have to go in and make some adjustments.
Digitally printing the bright red portions of this fire truck — especially on a dark garment —
requires a fairly heavy white underbase and, possibly, some highlight white on top.
requires a fairly heavy white underbase and, possibly, some highlight white on top.
One of the most important things to do when trying to produce an
underbase for digital printing or screen printing is to have your art on
a transparent layer. Once your art is on a transparent layer you can
switch the background layer from black to white. You must have your art
on a black-and-white background for this to work properly. This is the
case whether you use the RIP software to create the underbase or create
that channel manually as I’ll show you in this article.
There are two basic types of underbases: solid and tonal (see box,
p.80). Which you choose depends on the type of artwork you plan to print
— vector artwork or raster (a.k.a., bitmap) art. I mostly print raster
images, which require tonal underbases. I create mine using the
luminosity of an image, which I can manipulate in Adobe Photoshop. To
access the luminosity of an image, you have to use the Lightness channel
in the Lab color mode in Photoshop.
To get started creating a digital underbase, first be sure your artwork
is on a black background then duplicate your image and change the mode
to Lab color. (From the top menu, pull down Image > Mode > Lab
Color). Once that’s done, go to your Channels palette and select the
Lightness channel. Now, using your mouse, click-drag the Lightness
channel from your duplicate window and drop it on your working file.
With this channel selected, invert the channel by selecting Image >
Adjustments > Invert from the top menu, or use the keyboard shortcut
Cmd-I/Ctrl-I (for MacOS and Windows, respectively).
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When you click-drag the Lightness channel from your duplicate image and drop it on your working file, you can see that it shows up as an Alpha channel in the original file. |
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When you invert that Alpha channel, it can be helpful to rename the channel “whitebase” (or whatever your preference might be) as I’ve done here. |
Next, go to Image > Adjustments > Curves to open the Curves dialog
box. Be sure your grid is in 10% increments and not 25%. All you have
to do is put your cursor on the grid and Opt-click (Mac) or Alt-click
(PC) inside the grid to change the size of the squares. Drag the nodes
at each corner to look like the image below. That’s it! This is the
adjustment I use 90% of the time. Occasionally, I make some further
adjustments if necessary.
Adjusting Curves: Dragging the nodes in the Curves dialog box
customizes the density of your “whitebase” channel.
customizes the density of your “whitebase” channel.
Look at the artwork and determine in what areas you may need a denser
white underbase. The underbase should be darker under the lighter colors
of the image. Remember: if you are printing a bright red on a dark
shirt, you’ll need a lot of white under that red to make the final print
bright.
You can learn a lot about separations and color from the Info palette in Photoshop. If you’re not familiar with this palette, make it a point to start using it. The Navigator/Info/Histogram palette should be open by default. If not, just press the F8 key or, from the top menu, select Window > Info.
Turn the preview “eye” icon on and off of your channels and experiment. With the “whitebase” channel visible, move your cursor around the image and watch the Info palette. It will show you exactly how much white you have in any area based on the density shown in the Info panel. Be sure to mouse over red areas of your image. If the Info palette shows 40% to 50% coverage, you may want to increase that to 80% to 100%. That is a hard-and-fast rule. If the final print should be a brilliant red, you should boost the underbase to ensure it prints nice and bright. Otherwise, the final print will look like brick or maroon red if printed without enough underbase white.
You can learn a lot about separations and color from the Info palette in Photoshop. If you’re not familiar with this palette, make it a point to start using it. The Navigator/Info/Histogram palette should be open by default. If not, just press the F8 key or, from the top menu, select Window > Info.
Turn the preview “eye” icon on and off of your channels and experiment. With the “whitebase” channel visible, move your cursor around the image and watch the Info palette. It will show you exactly how much white you have in any area based on the density shown in the Info panel. Be sure to mouse over red areas of your image. If the Info palette shows 40% to 50% coverage, you may want to increase that to 80% to 100%. That is a hard-and-fast rule. If the final print should be a brilliant red, you should boost the underbase to ensure it prints nice and bright. Otherwise, the final print will look like brick or maroon red if printed without enough underbase white.
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Adjusting the density of the white underbase starts with selecting the Color Range… tool from the top menu. |
Adjusting the red areas of the image to get more white underbase is
pretty simple. Here’s how: With your Color palette selected, from the
top menu pulldown Select > Color Range... When the dialog box comes
up, mouse over the image and click on a bright red area of the design.
Adjust the “Fuzziness:” slider to capture most of the color you want to
boost. Be careful not to get too much. While the area is selected,
highlight the whitebase channel. Go to Image > Adjustments >
Curves to open the Curves dialog box. Grab the middle of the diagonal
line and pull down to make the image darker. I boosted mine to about 80%
under my red.
Blues and greens normally don’t require extra underbase, though they sometimes do require a little tweaking. Red almost always needs extra underbase. By combining heavy and light areas throughout the shirt design, you give the final print the softest hand possible while also applying enough white underbase to make the reds really pop. In Photoshop, there are 10 ways to do everything. For this column, I’m going to show just one way. Learn this method first, then you can experiment and do things on your own.
Only direct-to-garment printers with the capability to print white ink will need an underbase channel in the image files it prints. These are the machines that are marketed as printing on darks. Inkjet garment printers that don’t have the extra white inkset are meant for printing only white or lightcolored shirts. If your printer does have the extra white ink for printing darks, it also must have RIP software so it will know what to do with those extra channels.
Some RIPS do a better job of underbasing than others. Most will autogenerate underbases, but those generally don’t meet my standards. Keep in mind that if you are still shopping for your first direct-to-garment printer, you will probably get a RIP bundled with it. When comparing various printers, I think it’s important to ask, “Can I create my own underbase or am I locked into the one that the RIP generates?” Most bundled RIPs will let you bypass the automatically generated channels, though some don’t allow that flexibility.
This curves dialog box adjustment will boost the white underbase
to about 80% under the selected red areas of the image.
to about 80% under the selected red areas of the image.
Blues and greens normally don’t require extra underbase, though they sometimes do require a little tweaking. Red almost always needs extra underbase. By combining heavy and light areas throughout the shirt design, you give the final print the softest hand possible while also applying enough white underbase to make the reds really pop. In Photoshop, there are 10 ways to do everything. For this column, I’m going to show just one way. Learn this method first, then you can experiment and do things on your own.
Only direct-to-garment printers with the capability to print white ink will need an underbase channel in the image files it prints. These are the machines that are marketed as printing on darks. Inkjet garment printers that don’t have the extra white inkset are meant for printing only white or lightcolored shirts. If your printer does have the extra white ink for printing darks, it also must have RIP software so it will know what to do with those extra channels.
Some RIPS do a better job of underbasing than others. Most will autogenerate underbases, but those generally don’t meet my standards. Keep in mind that if you are still shopping for your first direct-to-garment printer, you will probably get a RIP bundled with it. When comparing various printers, I think it’s important to ask, “Can I create my own underbase or am I locked into the one that the RIP generates?” Most bundled RIPs will let you bypass the automatically generated channels, though some don’t allow that flexibility.
To get a bright inkjet print
of vector artwork (left) requires a solid white underbase, while
printing the same image in raster or bitmap format (right), requires a
less dense, tonal underbase. The black portion of each inset is the
white underbase channel for each.
The logic behind auto-underbase is that most people don’t know how to
create an underbase channel themselves and don’t want to go the extra
step. However, I believe you can do a better job than the RIP, and it
usually only takes a minute or two. Personally, I don’t want the RIP
creating channels for me; I want to bypass the RIP or use it only after I
have created my own channels. And not every shirt color needs an
underbase. Obviously, whites and lights do not need an underbase.
Examples of light colors are typically pastels such as yellow, khaki,
light blue or light gray. If it’s a lighter color, you can use just a
highlight white to finish it off.
Creating one underbase that will print a piece of art well on every color of dark shirt is the most efficient way to go. Some people who want to conserve ink might say, “Well, if I’m going to print a red shirt, I want the red of the shirt to be in the red areas of the design.” That requires one custom underbase. The inefficiency comes when you want to print that same job on five other colors; you’re going to drive yourself nuts creating individual underbases for each one.
Creating one underbase that will print a piece of art well on every color of dark shirt is the most efficient way to go. Some people who want to conserve ink might say, “Well, if I’m going to print a red shirt, I want the red of the shirt to be in the red areas of the design.” That requires one custom underbase. The inefficiency comes when you want to print that same job on five other colors; you’re going to drive yourself nuts creating individual underbases for each one.
One of the most common mistakes when creating underbases is not enough
coverage. It makes the images look dull and dead. You can fix those
things, but you have to test print.
PRETREATMENT
All inkjets that print white ink on dark shirts require some sort of garment pretreatment. Usually the pretreatment is a spray, so you spray the shirt and hit it with a heat press. This lays down all the fibers, giving you a nice, smooth garment to print. The pretreatment also helps ink to adhere to the garment, giving you a more vibrant final print and little or no fibrillation (small fibers sticking up out of the ink).
Once you have created your underbase, print a test shirt. Then, go back in and tweak the colors a little bit if necessary. That’s the learning curve. Once you get a feel for it, it’s not that tough and you’ll find you can create an effective underbase channel for any artwork in just a minute or two.
HIGHLIGHT WHITE
In order to get a really bright white in the finished inkjet print, you will need to print white as a highlight in just the white areas of the design. This is when a Highlight White channel comes in. It prints only over the white areas of the image and basically gives the white area a second hit of ink. An easy way to create the highlight white is to follow these steps:
With the artwork layer selected, go to Select > Color Range... In the Color Range dialog box, click on an area of the image that is bright white. Adjust the “fuzzy” slider — I usually stop around 30 on the slider — and click OK. While the white area is selected, create a new channel in your channels palette. Fill the selected area with Black. This data will print as white on the printer.
To make whites really pop on a finished digital print,
create a Highlight White channel that will hit the shirt
with a second, final spray of white ink.
PRETREATMENT
All inkjets that print white ink on dark shirts require some sort of garment pretreatment. Usually the pretreatment is a spray, so you spray the shirt and hit it with a heat press. This lays down all the fibers, giving you a nice, smooth garment to print. The pretreatment also helps ink to adhere to the garment, giving you a more vibrant final print and little or no fibrillation (small fibers sticking up out of the ink).
Once you have created your underbase, print a test shirt. Then, go back in and tweak the colors a little bit if necessary. That’s the learning curve. Once you get a feel for it, it’s not that tough and you’ll find you can create an effective underbase channel for any artwork in just a minute or two.
HIGHLIGHT WHITE
In order to get a really bright white in the finished inkjet print, you will need to print white as a highlight in just the white areas of the design. This is when a Highlight White channel comes in. It prints only over the white areas of the image and basically gives the white area a second hit of ink. An easy way to create the highlight white is to follow these steps:
With the artwork layer selected, go to Select > Color Range... In the Color Range dialog box, click on an area of the image that is bright white. Adjust the “fuzzy” slider — I usually stop around 30 on the slider — and click OK. While the white area is selected, create a new channel in your channels palette. Fill the selected area with Black. This data will print as white on the printer.
To make whites really pop on a finished digital print,
create a Highlight White channel that will hit the shirt
with a second, final spray of white ink.
Dane Clement, well-known for his expertise in computer graphics and color separations, works as an application specialist at SPSI in Minneapolis. Dane also is the founder of Great Dane Graphics, a supplier of high-quality vector artwork.
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