Color Optimization Guide

GDM Color Optimization Guide

This is the complete text version of the Color Galaxy. It covers everything you need to prepare files that print with the color you expect at Graphics Design Media in Las Vegas.

1. RGB vs CMYK: light vs ink

Screens build color by adding light. Red, green and blue pixels glow at different strengths, and at full power they add up to white. That is RGB, an additive color system.

Print works the other way. Cyan, magenta, yellow and black ink sit on a white surface and subtract light, absorbing some wavelengths and reflecting the rest. More ink means less light. That is CMYK, a subtractive color system.

A glowing screen can show colors that ink on a surface cannot reflect, so what you see on screen will never exactly equal print. The goal is to get as close as possible and to see the shift before you order.

How GDM prints your color: we print in CMYK. Standard jobs print the CMYK values in your file. When a brand color is critical, ask about a hard proof, and ask us about spot color or brand matching options by quote.

Convert before you upload

Switch your document to CMYK and convert RGB art yourself before you send it, so you see the shift and can adjust. The colors that shift the most:

• Very bright blues
• Bright greens
• Neons and fluorescents
• Saturated pinks and purples
• Very bright oranges

Why screens and print disagree

• Calibration: most screens are never calibrated and drift over time.
• Brightness: screens are usually far brighter than paper under room light.
• Display technology: OLED, LCD and wide gamut panels render color differently.
• Device: phones, laptops and monitors show the same file differently.
• Color profile: apps with and without color management show different results.
• Room lighting: warm lamps, daylight and office lights change what you perceive.

2. Gamut and out-of-gamut colors

A gamut is the full range of colors a device or process can reproduce. A typical screen shows more saturated color than ink on material can reflect, especially in the brightest and most vivid colors.

When a color is outside the CMYK gamut, conversion moves it inside. The hue stays as close as possible, but saturation or brightness drops. Electric blue can print as a deeper, slightly violet blue. Neon green prints as a calmer grass green.

Rendering intents

• Perceptual: shifts all colors slightly to keep relationships smooth. Good for photos with lots of vivid color.
• Relative colorimetric: keeps in-gamut colors exact and moves only out-of-gamut colors to the nearest printable color. Good for logos and flat brand colors. Use black point compensation with it.

Design inside the gamut

• Choose brand colors from CMYK values from the start.
• In Photoshop, View > Gamut Warning grays out colors that cannot print.
• Illustrator and Photoshop color pickers show a warning icon for out-of-gamut colors. Click it to snap to the nearest printable color.
• For real glow, use specialty materials such as holographic, metallic and reflective vinyl.

3. The Blue Rule

When cyan and magenta values are too close, magenta takes over and blue prints purple. Keep magenta at least 30 points below cyan.

• True blue: C100 M70 Y0 K0
• Strong blue: C100 M60 Y0 K10
• Navy: C100 M80 Y0 K40. Heavy black mutes the magenta cast, so deep navies are the one place a smaller gap still reads blue.
• Avoid: C100 M100 Y0 K0, which reads purple in print.

Pure RGB blue often converts automatically to roughly C92 M75, only 17 points apart. Check every blue after conversion and lower the magenta.

4. Rich black vs K100

Black in print is a recipe, and the right one depends on the size of the black area.

Small text, thin lines and fine detail should be K100 only. If a four color black shifts even slightly on press, colored halos appear around small letters. Large backgrounds get rich black.

5. Total ink coverage (TAC)

Total area coverage is C + M + Y + K at the darkest point of your file. Four inks at 100% add up to 400%.

Too much ink causes slow drying, smudging, ink transferring onto the next sheet and muddy shadows. Check total ink with the Info panel in Photoshop or Output Preview in Acrobat. To fix it, pull back cyan, magenta and yellow in deep shadows, use a controlled rich black, or convert with a profile whose ink limit matches the material.

6. Materials change color

The same file looks different on vinyl, banner, fabric, paper, coroplast, PVC, foam board, acrylic and aluminum. The causes are the white point of the material, its texture, its gloss and how much ink it absorbs.

• Gloss vinyl: richest color and deepest blacks, with glare under direct light.
• Matte vinyl: softer contrast and no glare.
• Vinyl banner: slight scrim texture and a little less saturation.
• Fabric: ink sits in the weave, colors soften, and large blacks need rich black.
• Uncoated paper: dot gain makes colors darker and duller on a warmer white.
• Coroplast: bright white, but flutes can show in flat colors.
• Acrylic: glassy depth that makes color pop. Watch reflections.
• Clear material without white ink: color is translucent and the background shows through.
• Clear material with white ink: the white underlay makes color solid and opaque.
• PVC and foam board: smooth, bright and fairly matte.
• Aluminum: print over a white base for solid color, or leave it bare so the metal shows.

Other factors that change color: the substrate, ink coverage, equipment, print process, environment, finish (gloss, matte or laminate), indoor vs outdoor light and viewing angle. When one brand is printed on several materials, expect small differences and consider a proof on each.

7. Pantone, spot color and neon

Pantone (PMS) colors are standardized spot colors, each a specific premixed ink. Our process builds color from CMYK, so spot colors are printed as CMYK builds. Convert them yourself first, using a CMYK bridge guide that shows each spot color beside its closest CMYK build.

Some spot colors are outside the CMYK gamut and will print duller: bright oranges, reflex style blues, rhodamine style pinks and purples, and all neons.

Neon and fluorescent colors cannot be made with CMYK. Fluorescent pigments absorb invisible and blue light and give it back as extra visible color, which process ink cannot do. Choose the closest in-gamut color, or use specialty materials such as reflective, metallic, chrome or holographic vinyl.

Standard GDM jobs print the CMYK values in your file. For brand-critical color, ask about a hard proof, and ask us about spot color or brand matching options by quote.

8. Gradients, banding and dot gain

Banding is when a smooth gradient prints as visible stripes. It is most likely in subtle gradients, dark gradients and gradients that stretch a small change over a large area or squeeze a big change into a short distance.

• Add 1 to 2% noise over the gradient (Filter > Noise > Add Noise in Photoshop).
• Avoid ending at exactly 0%. End at a light tint instead.
• Avoid tiny tonal steps across huge areas.
• Check gradients again after CMYK conversion.

Print makes tones with halftone dots. On uncoated stock the ink spreads, dots grow and colors print darker, which is called dot gain. Tints under about 5% may vanish, and tones of 95% and above may fill in to solid.

9. Resolution and viewing distance

Resolution is measured in pixels per inch at the final printed size. Effective ppi equals image pixels divided by print inches. For example, a 3000 pixel wide image printed 10 inches wide is 300 ppi, and printed 20 inches wide it is 150 ppi.

• Vector art is resolution free and stays crisp at any size.
• Do not upscale small images. Enlarging adds pixels but no detail.
• Proof at 100% zoom at final size to judge sharpness.

10. Profiles, proofing, overprint, white ink and export

ICC profiles

An ICC profile describes how a device reproduces color. Convert RGB art using a standard coated CMYK profile. GRACoL 2013 and Coated FOGRA39 are common choices.

• Assign Profile changes how existing numbers are interpreted. The numbers stay the same and the appearance changes.
• Convert to Profile changes the numbers to keep the appearance as close as possible. Use Convert when preparing print files.
• Rendering intents: perceptual for vivid photos, relative colorimetric for logos and flat brand color.

Soft proofing and hard proofs

• Soft proof with View > Proof Colors in Photoshop and Illustrator.
• Calibrate your monitor to about D65 white at 120 cd/m².
• Judge prints under daylight balanced D50 light.
• Metamerism means a color can match under one light and look different under another.
• Ask for a printed proof for brand-critical work.

Overprint and knockout

• By default a top object knocks out the colors beneath it. Overprint lays the top ink over what is underneath.
• Small black text should overprint so no gap appears if plates shift.
• White objects must never be set to overprint, or they disappear.
• Preview with Overprint Preview in Illustrator or Output Preview in Acrobat.

White ink

• Clear, metallic, holographic and colored materials need white ink underneath for opaque color.
• Build white as a separate spot color layer with a spot swatch named White.
• Choke the white slightly so it hides inside the color edges.
• Knock white out where you want the metallic or holographic material to show.

Export

• Press quality PDF: PDF/X-1a or PDF/X-4.
• Fonts outlined or embedded.
• Include 0.125 inch bleed.

11. Prelaunch checklist

1. Document is in CMYK mode
2. RGB images converted and reviewed
3. Pantone and spot colors converted to CMYK
4. Blues keep magenta at least 30 points under cyan
5. Large blacks use rich black, small text is K100
6. Neons and fluorescents reviewed
7. Resolution OK at final size
8. Text legible at final size
9. Gradients checked for banding
10. Total ink within limits
11. 0.125 inch bleed included
12. Exported as a print-ready PDF

A friendly note: screens cannot show final print perfectly, and small variation between devices, materials and production runs is normal. Following this guide gets you as close as possible.

Questions about your file? Call Graphics Design Media at (725) 910-5803, visit us at 4175 Cameron St, Suite 5, Las Vegas NV, or request a quote. Cutting a custom shape? Read our Die-Cut Printing Guide.