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Photoshop 911: Duotones
From: Kerala, India > I want to know about DUOTONES in Photoshop. > I mean, if I have a gray scale picture and I > wnat to print it in two colours. > What I have to do?
What are Duotones?
Contrary to popular belief, Duotones include only two colors. (Duh, not tri-tones or quad-tones, or others.) Additionally, duotones can be any two colors, and not necessarily one color plus black. I've seen some luscious printed pieces -- even produced a few myself -- using two PMS colors alone with NO blacks. I presented the entire process at one point in my "Color Builder" seminar marketed back in the '90s. There are also several very good software packages that allow you to predict, configure and produce stunning faux-4c color jobs using only 2 colors. In my live seminar I carry actual printed samples.
Anyway, duotones are a bit of trouble because you cannot accurately predict the results on consumer printers. You have to have a color proofing system capable of substituting real PMS colors in place of the 4-color process CYMK. Few printers offer this service, and before undertaking a duotone project I seriously recommend you seek the advice of your printer.
In effect, duotones are a combination of two grayscale images, using two negatives and two printing plates. Sometimes we see super print quality using two blacks, to add midtones or highlights to an image, or to extend an image's overall tonal range. Back in the '80s the Time-Life Photography series of books used Black and metalic Silver inks to produce probably some of the best high-grade black and white photographic images ever printed. They're no longer in print, but you can find them in most better public or university libraries.
The duotone effect is achieved by imaging the two negatives with different (sometimes very different) tonal ranges. If you're new to this I recommend first taking a look at Photoshop's pre-set duotone templates. Access them by clicking "Load" in the Duotone Options box, then navigating to the Adobe Photoshop directory to: Presets, then Duotone directory. You can modify these or run them as-is.
How to Make Duotones
Make sure the photo has a good overall tonal range, and good contrast. (Look at the Histogram: ideal would be solid black, no white stripes, and near level skyline with highs at the far left and right.) If you're using a color photograph, first convert it to grayscale by using
Image menu > Mode > Grayscale.
Open the First Diagram
Once your image is ready:
- Choose Image menu > Mode > Duotone.
- Check "Preview" so you can see your color and curves changes immediately.
- Choose Duotone from the pop-up "Type" button 
- Clicking the Ink color square will launch the color picker so you can set the color. Generally, the first slot is BLACK -- as it should be the darkest ink. The second slot should be the color. (Higher ink numbers should be the lighter ink colors.) 
- Once you've selected the color, its name will appear in the field 
- The 'Curve' button allows you to modify the tonal range of that color. 
Selecting the Colors
Open the Second Diagram
Clicking on the Color Square initiates the color picker. From there you select
- The ink specification
- The color "Name" or
- your own custom "build" or process color (Not recommended)
- Make sure you select a color matching system your print shop supports.
See what colors they stock because mixing color for a small job can get expensive. Also, make sure to select the color type that works best with the paper you intend to use.
Open the Third Diagram
Depending on the image, the paper, and the sophistication of the printing equipment these curves can have quite a bit of effect on the finished piece. A flat, diagonal line will print both colors at the same gray value with an even color range. Sometimes this is best, but it will load up in the dense areas, and flatten the highlight areas.
In today's example I use plain process yellow for my second color. If you left Diagram 2 open, notice the color differences between that and #3. The color in Diagram 2 is a flat color ramp for both colors. You probably will want a less garrish color, and besides when mixed with black ink on the press, the midtones will have a greenish look.
Notice the curve box is ticked off in 10% increments, with the left (1) being the deepest shadows, 5 being the midtones (2) and 9, 10, being the lightest highlights (3).
For your first time out, go ahead and experiment with the settings.
For example, to reduce the amount of ink coverage in the deep shadows of the image, you would set a lower percentage of ink in the box labeled "100%". So, if you're printing black and one color, you may want to reduce the amount of color in the deep shadows because it really does little good there. In the same respect you may want less black in the highlight areas since the combination of black and color increases ink density anyway. So, you would possibly set a lower percentage in the 5, and 10 boxes.
Again, caution is advised, and generally speaking the Photoshop pre-sets are good starting places.
The curve I've selected here represents color encroaching only into the middle tones of the image, leaving the highs and lows virtually untouched. If I were to actually print this example, it would probably look pretty awful.
Once you think you've got it, you need to SAVE the file as EPS. This is best for most imaging equipment and keeps the halftones pristine. You may even want to save the file as native Photoshop to send along so if the technician needs to do some tweaking the original images are present.
If you're going to use the Duotone in a Desktop publishing program like Quark XPress, PageMaker or InDesign, you'll want to use the "SHORT" names for the PMS colors. You can set that in your Preferences under Edit > Preferences > General.
That's all there is to it.
Be sure to see our article "Duotones" fromDr. D'Lynn Waldron which includes a good reference section on Pantone color products for producing really accurate duotones and 4/c print color.
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