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Duotones: Photoshop to InDesign
What are duotones? From the Photoshop 7.0 Online help file:
Duotones are used to increase the tonal range of a grayscale image. Although a grayscale reproduction can display up to 256 levels of gray, a printing press can reproduce only about 50 levels of gray per ink. This means that a grayscale image printed with only black ink can look significantly coarser than the same image printed with two, three, or four inks, each individual ink reproducing up to 50 levels of gray.
Sometimes duotones are printed using a black ink and a gray ink–the black for shadows and the gray for midtones and highlights. More frequently, duotones are printed using a colored ink for the highlight color. This technique produces an image with a slight tint to it and significantly increases the image’s dynamic range. Duotones are ideal for two-color print jobs with a spot color (such as a PANTONE Color) used for accent.
Duotones is a generic name given to monotone, duotone, tritone etc images. The mono- prefix here denotes the number of colourants (plates) in the final file generated by Photoshop.
Generating Duotones from Photoshop
The greatest control over true Duotones as defined above is going to be in Photoshop. However, there is a concept known as fake or poor man’s Duotones, which InDesign 2.0 supports directly.
The process of converting a coloured image into a Duotone in Photoshop starts with converting the image to grayscale. The quickest, and rawest method of converting is to go Image>Mode>Grayscale
After converting to greyscale, the next step is to Image>Mode>Duotone change the grayscale into a Duotone image. The dialog box that appears allows you to change the spot colour that makes up the second colour. If you would prefer a monotone, change the first “Black” ink in the list to the spot colour. The curve box permits tweaking of the ink density where the second colour is applied.
How do you get Photoshop Duotones into InDesign 2.0.x?
To place this file in InDesign, the format that we need to save the file is Photoshop EPS. Photoshop EPS is a nice, Composite format that permits us to print composite output; including Composite PDF. I am not a major fan of Photoshop DCS as a format. (ref: InDesign 2.0: Photoshop with Spots, InDesign and Composite PDF)
In InDesign, File>Place the Photoshop EPS saved above. Once the image is placed, you will notice that InDesign adds a new Swatch to the Window>Swatches palette.
From this point, the new Swatch is considered a Spot colour. Managing this is the same as managing Spot colours in InDesign: through the Ink Manager.
Note: There is a known (and you do read Readme’s, right?) a documented bug with InDesign 2.0: it considers the spot colour’s alternate colour space RGB. This means, if you print separations where you have Ink aliased the Spot to Process in the Ink Manager, it converts the Spot specified in the Photoshop EPS to RGB rather than the CMYK alternate. The workaround is to make this element 99.9% Normal Transparency, and print using the [High Resolution] Transparency flattener style. The Flattener will correctly convert the Spot to its CMYK (Process) breakdown, and permit a pure Process output. (ref: InDesign 2.0: Printing Output Choices and Flattener Tricks (including force Greyscale export!))
Poor Man’s Duotones in InDesign
Grayscale images can be directly made into Monotones in InDesign 2.0. Here, we are assigning the Black (K) plate to an alternate colour, including potentially a Spot Color. The user-interface needs to be carefully described as there is a little twist: something the help file doesn’t quite explain. The order of steps below are critical!
- Place the Grayscale TIFF or Photoshop image into InDesign 2.0
- Open Windows>Swatches
- Ensure that the Swatch, Spot or otherwise is in the Swatches list
- Select the Direct Selection Tool
- In the Swatches palette, ensure that the Fill is selected at the top:
- Click inside the Greyscale image with the Direct Selection Tool
- Click on the Swatch you would like to apply to the image:
The key to this process is ensuring that you have the Fill selected in the Swatches prior to Direct Selecting the content of a greyscale image. I do not think the online help in InDesign 2.0 clearly explains these steps.
Thanks to Gene Palmiter for suggesting I write this up. Its been in my head for months.