Photoshop also allows you to work with spot colors (also referred to as custom colors). If you need to match a specific color used in a corporate logo, or if you’d like to include a bright orange, green, or metallic color that you can’t achieve with CMYK process inks—spot colors are the way to go. They can also be used to create duotones and tint effects, or can be combined with grayscale in a two- or three-color design.
Spot Color Defined
Four-color process is a printing method that produces a wide range of colors by overlapping halftones (tints) of four colors: cyan, magenta, yellow, and black. Our eyes blend these halftones together, and allow us to see the various colors used in the design the way we’re supposed to. Spot color printing on the other hand, does not overlap halftones. Instead, these specific, premixed inks are printed on separate plates. Spot colors can be added to a four-color process print job by printing them alongside or on top of process-color images. This is what is sometimes referred to as a fifth or sixth color. For example, a metallic color or a varnish that cannot be simulated in process-color printing can be added to a four-color process print design by using spot color plates. You can also enhance a specific color in a CMYK image by adding a spot color “bump” plate.
Adding a Spot Color Channel
Adding a “fifth” color to a four-color process CMYK file in Photoshop means adding a fifth channel, called a spot color channel. To add a spot color channel, choose New Spot Channel from the Channels palette menu. You can also do this by F/Ctrl+clicking the New Channel button at the bottom of the palette. In the dialog box that appears, click the color swatch to launch the Color Picker. Click the Color Libraries button and choose a spot color swatch book type from the Book drop-down list. The default color model is Pantone Solid Coated. Note that the Book dropdown list includes process-color swatch books in addition to spot color books, even though they are meaningless here. Choose a color from the list and click OK. Photoshop automatically places the chosen spot color swatch’s name in the New Spot Channel dialog’s Name field.
The value entered in the Solidity field determines how the spot color will be displayed onscreen. This allows you to preview onscreen what the overlapping spot color will look like when printed. At 100% solidity, the color is completely opaque (metallic inks); at 0% solidity, it is transparent (varnishes). If you’re not sure what solidity value to use, your printer can provide you with the proper settings for chosen spot colors.
After you create the spot color channel, Photoshop automatically selects it for you. You can then paint or add text in the channel by using black, white, or gray. Black represents solid spot color, white represents no ink at all, and gray is a tint of the spot color. When you are finished painting or adding text, return to the composite RGB or CMYK channel by selecting it in the Channels palette or by pressing F/Ctrl+~ .
Converting Alpha Channels to Spot Channels
Photoshop also allows you to convert a regular alpha channel into a spot color channel. To do so, doubleclick the alpha channel in the Channels palette to access the Channel Options dialog box. Then select the Spot Color radio button, choose a color and solidity value, and click OK.
Converting Layers to Spot Colors
One frustrating thing about working with spot colors in Photoshop is that you can’t use them with layers. However, you can work around this by setting up the spot color artwork in a layer before you add the spot channel. Follow these steps:
1. In a new layer, choose black as the foreground color and add any text or brush strokes that you’d like to print in a spot color.
2. F/Ctrl+click the layer icon in the Layers palette to load a selection of the spot color artwork.
3. Now create the spot color channel. Photoshop automatically fills the selection with black in the spot channel.
4. Hide or delete the layer.
Spot Color Knockout and Trapping
Spot color inks (with the exception of metallic inks) are never fully opaque. As a result, trying to print a solid PMS ink over a CMYK image generally results in mottled color. To avoid overprinting problems, you must manually knock out the image areas underneath the spot color (unless you are using spot color as a “bump” plate or a varnish, in which case you will always want to overprint and not knock out).
Knocking Out Manually in Photoshop Layout applications such as InDesign and Quark-XPress automatically knock out the areas underneath a spot color when the file is output, but that is not the case in Photoshop. You must use the following procedure to knock out the image areas manually:
1. Load a selection based on the spot color channel by F/Ctrl+clicking its thumbnail in the Channels palette.
2. If the background colors are lighter than the overlying spot color, contract the selection to accommodate for trapping (see the next section for more on this technique).
3. Create a new layer in the Layers palette.
4. Choose Edit --> Fill to access the Fill dialog box, and then fill the selection with white. You could fill the background with white rather than creating a new layer, but this would not allow you to make a change later, should you need to. If you have two spot colors that overlap, you need to knock out only the image area beneath the lower spot channel.
Trapping Trapping is a process that compensates for any misregistration that occurs on press. Paper shift is inevitable on a printing press, and this is what causes misregistration. When working with spot colors, you must make sure that your knockouts are trapped properly. Otherwise, a white sliver will appear between abutting colors in your print job. When building traps in Photoshop, the basic rule to follow is to always make the lighter color overlap the darker color. If the background color is lighter than the spot color, you must choke the background by making the area that you knock out slightly smaller. After loading the spot color channel as a selection (see step 1 in the preceding knockout procedure), choose Select --> Modify --> Contract and enter a value of 1 pixel in the dialog that appears. Click OK to apply the modification, and complete steps 3 and 4 as described in the previous section.
If the spot color is lighter than the background, you must spread the spot color. After you knock out the underlying image area by using the preceding steps, select the spot color channel in the Channels palette and choose Filter --> Other --> Minimum. The Minimum filter allows you to expand the image in the channel so that it overlaps the background. Enter a 1-pixel amount in the dialog box that appears and click OK. If your printer gives you a specific trap size to use in millimeters or points, you may want to use Photoshop’s Trap dialog box instead. Convert the image to CMYK mode, and then select the spot color channel in the Channels palette and choose Image --> Trap. Choose millimeters, points, or pixels from the menu in the dialog, enter the value, and click OK.
Saving Images with Spot Colors
After you’re finished preparing spot color graphics in Photoshop (including duotones, described in the next section), you’ll need to save them in a specific file format in order for them to output properly. The file format you should use depends on what layout application you’ll be placing the images in. If you’re using QuarkXPress, save the images in the DCS 2.0 format. If you’re using InDesign, save them in either the DCS 2.0 or the native Photoshop (PSD) format.
Spot Color Defined
Four-color process is a printing method that produces a wide range of colors by overlapping halftones (tints) of four colors: cyan, magenta, yellow, and black. Our eyes blend these halftones together, and allow us to see the various colors used in the design the way we’re supposed to. Spot color printing on the other hand, does not overlap halftones. Instead, these specific, premixed inks are printed on separate plates. Spot colors can be added to a four-color process print job by printing them alongside or on top of process-color images. This is what is sometimes referred to as a fifth or sixth color. For example, a metallic color or a varnish that cannot be simulated in process-color printing can be added to a four-color process print design by using spot color plates. You can also enhance a specific color in a CMYK image by adding a spot color “bump” plate.
Adding a Spot Color Channel
Adding a “fifth” color to a four-color process CMYK file in Photoshop means adding a fifth channel, called a spot color channel. To add a spot color channel, choose New Spot Channel from the Channels palette menu. You can also do this by F/Ctrl+clicking the New Channel button at the bottom of the palette. In the dialog box that appears, click the color swatch to launch the Color Picker. Click the Color Libraries button and choose a spot color swatch book type from the Book drop-down list. The default color model is Pantone Solid Coated. Note that the Book dropdown list includes process-color swatch books in addition to spot color books, even though they are meaningless here. Choose a color from the list and click OK. Photoshop automatically places the chosen spot color swatch’s name in the New Spot Channel dialog’s Name field.
The value entered in the Solidity field determines how the spot color will be displayed onscreen. This allows you to preview onscreen what the overlapping spot color will look like when printed. At 100% solidity, the color is completely opaque (metallic inks); at 0% solidity, it is transparent (varnishes). If you’re not sure what solidity value to use, your printer can provide you with the proper settings for chosen spot colors.
After you create the spot color channel, Photoshop automatically selects it for you. You can then paint or add text in the channel by using black, white, or gray. Black represents solid spot color, white represents no ink at all, and gray is a tint of the spot color. When you are finished painting or adding text, return to the composite RGB or CMYK channel by selecting it in the Channels palette or by pressing F/Ctrl+~ .
Converting Alpha Channels to Spot Channels
Photoshop also allows you to convert a regular alpha channel into a spot color channel. To do so, doubleclick the alpha channel in the Channels palette to access the Channel Options dialog box. Then select the Spot Color radio button, choose a color and solidity value, and click OK.
Converting Layers to Spot Colors
One frustrating thing about working with spot colors in Photoshop is that you can’t use them with layers. However, you can work around this by setting up the spot color artwork in a layer before you add the spot channel. Follow these steps:
1. In a new layer, choose black as the foreground color and add any text or brush strokes that you’d like to print in a spot color.
2. F/Ctrl+click the layer icon in the Layers palette to load a selection of the spot color artwork.
3. Now create the spot color channel. Photoshop automatically fills the selection with black in the spot channel.
4. Hide or delete the layer.
Spot Color Knockout and Trapping
Spot color inks (with the exception of metallic inks) are never fully opaque. As a result, trying to print a solid PMS ink over a CMYK image generally results in mottled color. To avoid overprinting problems, you must manually knock out the image areas underneath the spot color (unless you are using spot color as a “bump” plate or a varnish, in which case you will always want to overprint and not knock out).
Knocking Out Manually in Photoshop Layout applications such as InDesign and Quark-XPress automatically knock out the areas underneath a spot color when the file is output, but that is not the case in Photoshop. You must use the following procedure to knock out the image areas manually:
1. Load a selection based on the spot color channel by F/Ctrl+clicking its thumbnail in the Channels palette.
2. If the background colors are lighter than the overlying spot color, contract the selection to accommodate for trapping (see the next section for more on this technique).
3. Create a new layer in the Layers palette.
4. Choose Edit --> Fill to access the Fill dialog box, and then fill the selection with white. You could fill the background with white rather than creating a new layer, but this would not allow you to make a change later, should you need to. If you have two spot colors that overlap, you need to knock out only the image area beneath the lower spot channel.
Trapping Trapping is a process that compensates for any misregistration that occurs on press. Paper shift is inevitable on a printing press, and this is what causes misregistration. When working with spot colors, you must make sure that your knockouts are trapped properly. Otherwise, a white sliver will appear between abutting colors in your print job. When building traps in Photoshop, the basic rule to follow is to always make the lighter color overlap the darker color. If the background color is lighter than the spot color, you must choke the background by making the area that you knock out slightly smaller. After loading the spot color channel as a selection (see step 1 in the preceding knockout procedure), choose Select --> Modify --> Contract and enter a value of 1 pixel in the dialog that appears. Click OK to apply the modification, and complete steps 3 and 4 as described in the previous section.
If the spot color is lighter than the background, you must spread the spot color. After you knock out the underlying image area by using the preceding steps, select the spot color channel in the Channels palette and choose Filter --> Other --> Minimum. The Minimum filter allows you to expand the image in the channel so that it overlaps the background. Enter a 1-pixel amount in the dialog box that appears and click OK. If your printer gives you a specific trap size to use in millimeters or points, you may want to use Photoshop’s Trap dialog box instead. Convert the image to CMYK mode, and then select the spot color channel in the Channels palette and choose Image --> Trap. Choose millimeters, points, or pixels from the menu in the dialog, enter the value, and click OK.
Saving Images with Spot Colors
After you’re finished preparing spot color graphics in Photoshop (including duotones, described in the next section), you’ll need to save them in a specific file format in order for them to output properly. The file format you should use depends on what layout application you’ll be placing the images in. If you’re using QuarkXPress, save the images in the DCS 2.0 format. If you’re using InDesign, save them in either the DCS 2.0 or the native Photoshop (PSD) format.
Applying Spot Color in Photoshop
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