Color Models
Color is relative to what it is reflecting upon and from what direction. In the instance of pre-print production, the two variables we need to be aware of are light and pigment.

Backlit Color
Color, when viewed on the monitor, reflects light from behind and through to the eye. This backlit effect will tend to make the color brighter and more vibrant. The monitor uses a color model based on the primary colors of red, green and blue (RGB). Monitor color is additive, meaning, when all colors are blended together, they make white.

Saturation
Saturation is the intensity, clarity, purity or chroma of a color. It is the barometer of how much dilution by another color is also included. On the CIE chart, saturation decreases as we move from the pure color at the edge toward the grayer center.

Value has to do with lightness or darkness of the hue, how much white or black is added to create a tint.

CMYK or Spot Color in Relationship to Printing
Each color that is printed is separated onto its own piece of film and subsequent plate. Spot colors are used either when fewer than four colors are being specified, or when the specific color needed is not available in the CMYK build. This occurs when the use of a very intense, large expanse of color is needed, say on a box cover, for example. Because ink is semi-transparent, sometimes this color will even be run through the press twice (called a double bump) or will be underprinted with white to intensify the brilliance. If it is being printed over another expanse of color, the under color can also be knocked-out below the intense color to allow the overprinted color to stay pure. Another instance where a spot color might be used with pastelles, flourescent colors or metallic colors. When spot color is added to the cmyk process, a fifth plate has to be added to the cost of the project. A sixth plate will need to be addded if a varnish or aqueous coating is printed over the entire piece or in spots for added emphasis and protection, on say a box or book cover.

Scanned and computer generated RGB colors must be translated to CMYK or PMS spot color for printing, and in the process, some color shifts. Because the color gamut is more limited in the CMYK range than the RGB range, yellows can be translated more successfully than greens and blues. Paper stock also plays a role in color shift. Color stays fairly robust on coated stock, because the ink stays on the surface. More porous papers, like newsprint, recycled and uncoated stock in general, desaturae color as it is absorbed. The perception of color also alters depending upon juxtaposition of color next to color. The same tint of a hue will look different when next to a more saturated swatch of itsself, black or a lighter tint of itself, as well as its complement on the color wheel.

Creating Monotones, Duotones, Tritones and Quadtones

Greyscale images can be enriched by adding screened-back color to the mix. A monotone is a grayscale image printed with a single, nonblack ink. Duotones, tritones and quadtones are grayscale images printed with two, three and four inks.

A grayscale image can contain up to 256 levels of gray within its digital information, but the printing press can only reproduce about 50 levels of grey per ink screen. Multitoned images contain a screen for each ink specified, so this tonal range is increased by 50 each time another ink screen is added to the mix. Most often, multitones are printed using black and other colors.

In the case of a duotone, black will usually be used for the shadows and midtones, and the other color for the highlights. This produces an image with a slight tint of the color and greatly enrichens the tonal range. Duotones are ideal for a two color job with a spot color ink used for accent.

A tritone would have the darkest color assigned to the shadow range (from 100%–66%), the middle range assigned to midtones (65%–33%), and the lightest color to the highlights (0–34%). This produces an image with multiple tints and interesting complexity. Tritones are obviously suited for a three color job.

A quadtone would have the darkest color assigned to the shadows (from 100-75%), next darkest color for the upper midtones (74–51%), next darkest for lower midtones (50-26%), and lightest for highlights (0-25%). Quadtones can be created using the CMYK build or using four spot colors. If a quadtone was created with spot colors and combined within a CMYK project, eight plates would be required and could be quite costly.

Photoshop has an excellent production option for creating multitone images. Because multitone images are really just greyscale images with color added to it, the Photoshop file is a single-channel, 8-bit greyscale image rather than a multiple-channel image like an RGB or CMYK image. You can still manipulate each color’s curves in the Duotone Options dialog box, but they all live within one channel.

4. Click the Color box (the solid box) for the first ink and choose a custom color Pantone formula to apply to the inking screen/plate. You will need to use the exact same color naming convention in the page layout program. (Pantone 1787 in Photoshop=Pantone 1787 in Quark, not “salmon pink” in one but not the other) Choose a Pantone formula for each color. The darkest ink should be selected first and incrementally to the lightest, because the order of inks affects how Photoshop applies the screen.

5. Click the Curve box specifies how the ink will be distributed across the shadow and highlighted areas. The curves maps each grayscale value on the original image to the actual ink percentage that will be used when the image is printed. A diagonal curve will cause even distribution of ink throughout the image (50%midtone pixel prints with a 50% dot of the ink, 100% shadow pixel with a 100% dot of the ink, etc.). Make notes on the percentages you specify for possible export into the page layout file later.

Adjust the curves by moving th e handles on either end of the curve and adding handles along the curve by clicking on it. The horizontal axis moves from highlights at the left to shadows at the right. Ink density increases as you move up the vertical axis. The curve can contain up to 13 points. Photoshop calculates intermediate values between points along the curve.

6. If you prefer, you can specify values along the curve within the % dialog boxes. They two options work in synchronization.

7. Click save in the dialog box to save the settings. If you want to edit the duotone at a later date, the same settings will still be in the dialog box when you return. They can also be loaded and applied to other photos at a later date.

Jeff Goltz at Starlink in Torrance, CA has a suggestion for pre-press preparation through their RIP.

Convert the Duotone into a CMYK Image

1. Open the duotone.

2. Select Mode-Duotone-to see which color is in which postion.

3. Go to Mode: select Multichannel

4. Select channel #1 (this will be Color #1 from the Duotone), select all (Command/Cntrl A) and cut contents.

5. Select Mode: Greyscale, then CMYK. Paste contents into desired channel (ie. black into black channel, blue into cyan channel, etc.)

6. There will be an extra channel at the bottom, it is the second color of the Duotone (#2 from Duotone). Cut these contents and place in desired channel (ie. black into black channel, blue into cyan channel, etc.)

7.Delete extra channel and Voilá, a CMYK Duotone.