Creating Spot Channels
Duotones and Spot Channels in Photoshop
Scenario: You are designing a piece which will be printed in two ink colors. Since you cannot reproduce full color images (CMYK) with two inks, you must prepare image files for spot color printing by converting them grayscale images and then creating duotones or spot channels.
(Pantone Gray 11
and Pantone 279)
with a spot channel
Grayscale, Monotone, and Duotone
A black and white photograph is called a grayscale image because it contains up to 256 shades of gray when it is printed.
A grayscale image that is printed in any single ink color other than black is called a monotone.
Images that are printed in two, three, or four ink colors are calledduotones, tritones and quadtones.
Duotones consist of two images which print on top of one another. Each image is printed in a different ink color. The duotone above is printed first in Pantone Gray and again in Pantone 279.
Duotones contain both colors throughout the entire image. By using aspot channel instead of a duotone, a second color can be applied to selected areas only.
Converting an Image to Duotone
Because duotones use different color inks to reproduce different gray levels, they are treated in Photoshop as single-channel, 8-bit, grayscale images.
In Duotone mode, you do not have direct access to the individual image channels (as in RGB, CMYK, and Lab modes). Instead, you manipulate the channels through the curves in the Duotone Options dialog box.
To convert an image to duotone:
1 Convert the image to grayscale by choosing Image > Mode > Grayscale. Only 8-bit grayscale images can be converted to duotones.
2 Choose Image > Mode > Duotone.
3 Select Preview to view the effects of the duotone settings on the image.
4 To specify the type of image, select Type: Duotone.
5 Specify the ink colors, click the color box (the solid square) for each ink.
6. Use the duotone curves to adjust the tonal range of each ink.
7 Click OK.
8. Save the image using the Photoshop (.psd) file format.
Using the duotone curves
1 Click the curve box next to the ink color box.
A. Highlights B. Midtones C. Shadow
The default duotone curve, a straight diagonal line across the grid, indicates that you are mapping the current grayscale value of every pixel to the same percentage value of the printing ink. At this setting, a 50% midtone pixel prints with a 50% dot of the ink, a 100% shadow with a 100% dot of the ink, and so on.
2 Adjust the duotone curve for each ink by dragging a point on the graph or by entering values for the different ink percentages.
Average key: original and corrected
High key: original and corrected
Low key: original and corrected
Creating Spot Channels
1. Choose Window > Channels to display the Channels palette.
2. To fill a selected area with a spot color, make or load a selection.
3. Choose New Spot Channel from the Channels palette menu.
4. Click the color box, and choose a color from a solid Pantone color library. The channel automatically takes the name of that color. Your selection will fill with the new spot color.
5 Click OK.
You may also add color areas to the image using any of the painting tools.
6. Save the file using the Photoshop (.psd) file format.