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Module 5 • Lesson 1🖨️ CMYK, Separations & Ink

A screen mixes light; a press mixes ink, and the two obey opposite physics. To deliver for print you have to think in subtractive color, four printing plates, and the hard limit of how much ink a sheet can hold. This is where beautiful screen work either survives the press or falls apart on it.

📚 What You'll Learn

By the end of this lesson, you will be able to:

  • Explain additive (RGB) vs subtractive (CMYK) color
  • Read the four process separations — C, M, Y, K — as printing plates
  • Respect total ink coverage (TAC) and why it matters on press
  • Understand GCR/UCR: replacing CMY overlap with black
  • Set overprint and know why trapping exists

⏱️ Estimated Time: 55 minutes

🎯 Project: One image converted to a press CMYK profile, its separations inspected, total ink checked, and small black text set to overprint.

In This Lesson

👤 The Goal: Print What You See

The same image, two color worlds. On the right, glowing RGB as it looks on screen — some of those saturated colors simply cannot be made with ink. On the left, the CMYK-gamut version: what the press can actually reproduce, slightly muted but honest. Knowing the gap, and controlling it, is prepress. Drag the handle:

CMYK RGB
A diagram of the principle. Those electric screen colors have no ink equivalent — the press can only mix from cyan, magenta, yellow, and black. Prepress is managing that gap deliberately, not being surprised by it.

🧠 Mental Model: Ink Subtracts

A screen starts black and adds red, green, and blue light to reach white — that's RGB, additive. Paper starts white and each ink subtracts light by absorbing wavelengths; stack cyan, magenta, and yellow and you approach black — that's CMYK, subtractive. Because ink can't absorb perfectly, CMY together makes a muddy brown, so a dedicated K (black) plate is added for true blacks, shadow depth, and crisp text.

The practical upshot: the printable gamut is smaller than your screen's, especially in vivid cyans, greens, and oranges. A color that glows on a monitor may be un-printable, and if you don't manage the conversion, the press decides for you — usually to your disappointment. Soft-proofing (Intermediate Module 2) is how you see the gap before it bites.

RGB — adds light black → white CMYK — subtracts light white → muddy dark (needs K)
Figure 1: Opposite physics. RGB builds up from black by adding light; CMY builds down from white by subtracting it — and because the inks are imperfect, K carries the true blacks.

🟦 The Four Separations

A CMYK file is really four grayscale plates, one per ink, each telling the press how much of that ink to lay down where. Open Window ▸ Channels after converting and you can view each: skin sits mostly in magenta and yellow, skies in cyan, and the K plate carries contrast and text. Reading separations is how you diagnose print problems — a muddy shadow is usually too much ink in all four plates at once.

Channels — CMYK plates
CMYK (composite) Cyan Magenta Yellow Black (K)
Figure 2: Four plates, one per ink. Each is a grayscale map of ink coverage; the press prints them in register to build the full-color image. Learn to read them and you can diagnose any print issue.

⚠️ Convert with the right profile, once

Don't just "Image ▸ Mode ▸ CMYK" with the default. Use Convert to Profile and pick the press's profile (e.g. GRACoL, FOGRA, or SWOP as a stand-in). Convert late, from your wide RGB master, and only once — repeated RGB↔CMYK round-trips degrade color every time.

💧 Ink Limits, GCR & Overprint

Total Area Coverage (TAC) caps how much combined ink a sheet can take — often ~300% (of a possible 400) for coated stock, less for newsprint. Exceed it and ink won't dry, sheets stick, and shadows plug into a black smear. The press profile enforces a limit, but you should sample your darkest shadows (the Info panel shows CMYK totals) and confirm they're within it.

GCR/UCR are how a profile hits that limit intelligently: where cyan, magenta, and yellow all overlap into grey, it replaces that overlap with black ink (Gray Component Replacement / Under Color Removal). This saves ink, keeps shadows neutral, and makes them more stable on press. Overprint matters for small black elements: set black text to overprint (print on top of color) rather than knock out, so tiny misregistration doesn't leave white gaps around the letters — the reason trapping exists.

✅ When in doubt, ask the printer

Every press, paper, and shop has its own profile, ink limit, and preferences. The professional move isn't memorizing one number — it's asking your printer for their profile and specs and setting up to them. Delivering to the actual press condition beats any generic default.

🛠️ Guided Build: Convert & Inspect

Open a finished, vivid RGB image (16-bit, wide gamut from Module 1).

Step 1: Soft-proof first · 8 min

  1. View ▸ Proof Setup to the press profile; toggle Gamut Warning to see which colors won't print, and gently pull those back.

Step 2: Convert to Profile · 8 min

  1. Edit ▸ Convert to Profile, choose the press's CMYK profile (or GRACoL/SWOP), Relative Colorimetric with Black Point Compensation.

Step 3: Read the separations & ink · 10 min

  1. In Channels, view each plate. Hover shadows with the Info panel set to show CMYK totals; confirm they're within the profile's TAC (~300%).

Step 4: Overprint the small blacks · 6 min

  1. Set small black text/rules to overprint (in the print workflow), so misregistration can't leave white halos. Save a copy tagged with the CMYK profile. 🏆

✅ Project Completion Checklist

  • ☐ Soft-proofed; out-of-gamut colors pulled in
  • ☐ Converted once to the correct press profile
  • ☐ Separations inspected in Channels
  • ☐ Shadow total ink within TAC
  • ☐ Small black elements set to overprint; profile-tagged copy saved

🧗 Now You: Solo Variation

🌟 Your challenge

  1. Convert the same image to a coated and an uncoated (or newsprint) profile and compare — the smaller-gamut, lower-ink profile changes everything.
  2. Deliberately build a 400%-ink shadow, then fix it with the profile's ink limit and watch the K plate take over via GCR.
  3. Sample a vivid brand color and check whether it's in CMYK gamut; if not, note that it may need a spot color (next lesson).

Going further: get a real printer's profile and spec sheet and set your whole document up to it. Delivering to a specific press condition is the difference between a proof that matches and one that argues.

🍳 Recipe Card: CMYK

Manage the ink, not just the color

  1. Soft-proof + Gamut Warning; pull impossible colors in
  2. Convert to Profile (the press's CMYK), once, late, from wide RGB
  3. Read the four separations in Channels
  4. Keep shadow total ink within TAC (~300%); trust profile GCR
  5. Overprint small blacks; ask the printer for profile & specs

Mantra: a press mixes ink, not light — design for what the ink can do.

📓 Learning Journal

Add to your journal after this lesson:

  • Key concepts you learned
  • Techniques that clicked for you
  • Questions or confusion points to revisit
  • Ideas you want to try
  • Your progress and feelings about learning this

✍️ This lesson's prompt: Find a print piece with rich blacks and a screen design with electric color. Describe, in ink terms, why one couldn't simply be the other.

🔭 Where This Leads

Four process inks can't do everything — some colors and effects need dedicated inks. Next: Lesson 5.2 — Spot Color, Duotone & Halftone, where Pantones, two-ink duotones, and the dot patterns a press actually prints come into play.

Should I work in CMYK the whole time?

No — edit in wide-gamut RGB (Module 1) where you have the most color and the most tools, then convert to CMYK late, once, for delivery. CMYK is a destination, not a working space; converting early throws away gamut you might have used.

Why does my print look darker/duller than my screen?

Two reasons: paper reflects less than a screen emits (soft-proofing with Simulate Paper Color shows this), and out-of-gamut colors were clipped inward. Both are expected — the fix is proofing and converting deliberately, and calibrating your monitor so the screen isn't lying.