Theresa Jackson operates Orchard View Color (Escondido, CA) and has more than 20 years experience in prepress, graphic design, color management and photography. Email her at [email protected]
Spot-color ink technology is common in the digital-print world. And, in UV-cure ink systems, white spot-color technology is a frequent option that, combined with the UV-ink characteristics, allows printers to creatively image on almost any substrate.
The channels palette (Window>Channels) manages Adobe Photoshop spot colors and, differently, Adobe Illustrator manages spot colors in the swatches palette.
In Photoshop, you can add a spot color to RGB or CMYK designs. A Photoshop RGB file has four default channels: composite RGB color, red channel, green channel and blue channel.
A CMYK file has five default channels: composite CMYK color, cyan, magenta, yellow and black. The channel palette numbers (listed on the right) show the quick-key command to view that channel. For example, command 3 (PC: control 3) displays the RGB-file red channel.
Define a new spot-color channel
Two Photoshop methods create a new spot channel: In the channel palette’s upper-right corner, click on the fly-out menu and choose the optional New Spot Channel. Or, command click (PC: control click) on the page icon at the bottom of the channel palette (third icon from the left).
Give the new spot channel a name and set the ink characteristics.
The spot-channel name is critical because some RIPs won’t otherwise recognize the color name and, therefore, won’t accept the channel as a special ink color. If you can’t predict the RIP action, give the channel a descriptive name. This also helps the machine operator understand your intent.
The Ink Characteristics tag has no bearing on prints. Its preview simply simulates the file color and ink density, and usually does a poor job.
Alpha channels versus spot channels
Determining the difference between an alpha and spot channel is difficult — both are eight-bit data with 256 gray levels (white to black). The only real difference is the intended purpose of the channel. To ascertain if a channel is an alpha or a spot, double click on the channel — or go to the panel fly-out menu.
The spot-channel information — added color data for printing — is in the File Preview.
The Channel Options allows you to convert the alpha channel to a spot channel. Simply select the third button, “Spot Color.”
You can’t convert a spot channel to an alpha channel.
Create a spot-color design
Channels doesn’t permit layers and editable text, so create the spot-color channel after you finalize the color design. The spot channel can include vignettes and feathered edges, plus soft and crisp-edged graphics.
Creating white-ink images requires you to think in reverse — 100% black in the spot channel represents 100% white ink.
How to preview your spot-color design
Ink Characteristics simulates how the design will print with all channels integrated. The Ink Characteristics Solidity view simulates ink density; Color simulates ink color. Unfortunately, Photoshop previews the spot color on top of the CMYK colors, which gives an inaccurate soft proof, especially for white-ink printing.
Use Photoshop layers to soft-proof spot-ink designs:
1. Create a new layer at the bottom of the layer stack (lowest priority). Fill it with the print substrate color.Advertisement
2. Create a second layer immediately above the substrate layer. Make a selection from the Spot Channel — command-click on the channel (PC. Control-Click). Fill the new layer with the spot-ink color.
3. If the design includes multiple layers, create a duplicate, flattened layer by selecting all layers in the layer’s palette (don’t include the two created in Steps 1 and 2) and click Command Option E.
4. Move this merged layer to the third priority, just above the spot-ink layer created in Step 2. To see an approximation of how the design will print, set the Layer Blend Mode to “Multiply” and switch off the original design layers.
Caution: Turn off or delete the three new layers before sending the file to print.
Printing and file formats
Native .PSD files can retain Spot Color channels, but RIPs won’t recognize them. Instead, keep a design copy in the native-layered .PSD format and save a flattened file for print output.
TIFF, Photoshop DCS and Photoshop PDF can retain spot-color information, and most RIPS recognize them. If you’re uncertain of the RIP requirements, save the design as a TIFF file. Make sure you select the “Spot Color” radial box in the Save Dialog box.
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