Sometimes you get a very clean piece of art with solid colors and you just want to do a simple set of separations. Although you could do a multi-color scan and then do a multi-color trace in CorelTrace or Adobe Streamline, it may be easier to just separate the entire design in Adobe Photoshop using the Color Range feature.
This short article will detail the simple step-by-steps that are necessary to do quick spot color separations. This procedure works with artwork that has solid colors or has gradations and shading. It will not work as well if there are a lot of colors or from a photorealistic image because you will probably need to pull more spot colors than you can print (figure 1).
Scan or Import the Image
Scan the art at at least 200dpi or higher at 100%. If possible, scan as millions-of-colors to give you very solid colors. Yes, you could scan at 256 colors but it may not give you hard, solid colors. The resolution of the scan will have a direct effect on the resolution of the final image. For the best and sharpest lines and overlay edges scan at 225 to 250dpi. Since the image will be scanned as a colored image, the file size could be very large at these resolutions. If you can, turn off “anti-aliasing� because you want as hard an edge as possible without the softening you get from anti-aliasing.
If the image was created or is from Corel Draw, Illustrator or Freehand, export the image at 225 to 250dpi with anti-aliasing turned off. This method is an excellent way to use the Corel Draw clip art that prints as CMYK in Corel.
The scan or imported image should be in RGB mode.
Select Each Color with Color Range
Open the image in Adobe Photoshop 4, 5, 5.5 or 6.0. (This routine will work in Photoshop 3.0 also, but some of the menu names are different.) To make this procedure easier, make sure the Channels Palette is open (Window/Show Channels). Go to Select and Color Range. This opens the very powerful Color Range feature. Make sure the Select window is set to Sampled Colors. Place the eyedropper over one of the specific spot colors in the image. Check Invert. You will see a black and white positive of the selected area in the small Color Range window. Adjust the Fuzziness slider to pull the amount of color you want. A low setting pulls just the color you selected. A higher number pulls a wider range of that color. You can see the color you selected in the Foreground Color box on the Toolbar (figure 2).
Save Your Selection
After you have a color selected and in the Color Range box, say OK to this dialog box. You will now see the famous “marching ants� around these specific colors. You need to save this selection by going to the Select pulldown menu and then to Save Selection. Approve the next dialog box. You will now have a 4th channel in the Channels Palette. In Photoshop Channels, if you check the small square box to the left of the image you will get and “eye� which makes the channel visible. By clicking on and off you can see how the channel looks. To see it by itself simply take the eye off the RGB channels. Look at the channel by itself to see if it is what you had in mind. If you click on the channel name, you have just selected the channel and you can now use the tools like the Tone Curve, and Filters on this channel. You can’t print out an RGB image as a separation BUT you can print out an individual channel. Any channel with an “eye� turned on will print. It is that simple! (Figure 3).
Repeat Steps Two and Three
Repeat steps two and three for the rest of the colors. When you are done you will have a new channel for each specific color (figure 4).
Spot color and trapping is not the strength of Photoshop, but trapping can be done. Trapping is where you increase the edge thickness of colors that print under the black plate. This helps images print easier and allow for misregistration caused by loose screens, sloppy press or vellum shrinkage. You generally want to do minimal or even no trapping. If you want to trap the image using the following method, the separation must be solid color with no shading or gradations. Before doing this make sure your Foreground Color is set to black! Select the channel you want to trap (also called a spread). Use the Magic Wand tool and select the area or areas you want to make fatter. Go to the Edit Menu and select Stroke. Use settings of 2 to 5 pixels depending on the resolution of your image and how much spreading you want. Select Outside and say OK. Photoshop will put an outline or stroke around this area and make it black – essentially making the select fatter (figure 5).
Preview the Image in Color
In order to see how the separations will print you should assign the correct color to each channel. By double-clicking on an individual channel name you can assign the correct color. Make the Opacity 100%. In Photoshop 5.0 and 5.5 you can make the channel a Spot Color. In fact Photoshop will also choose the nearest Pantone� color and put the color name in the channel header if you click on the Custom window when in Color Picker. Now, when you place an “eye� on one channel it displays in black and white. When you place the eye on more than one channel they display in color (figure 6).
Print Out The Files
If you have any shading areas in the image you will need to tell Photoshop what halftone frequency and angle you need. Go to File/Page Setup/Screens. Uncheck Use Printer’s Default. In Photoshop 4.0 drop down the ink menu and change the setting for the Black plate only to 45 lpi, 25 degree angle, ellipse dot shape. In Photoshop 5.0 and 5.5, you will see you spot color plates and need to change the frequency, angle and shape for each channel. In the main Page Setup menu, check Registration Marks, and Labels. Next, go to File/Print, and print out each file that has an “eye� turned on. You will need to select Grayscale (figure 7).
That’s it. A quick and simple way to make spot color separations in Adobe Photoshop.