| PRE-PRESS | Jaina Offset Team
What is CMYK and Why It Matters for Offset Printing
If you are preparing artwork for offset printing, you will hear the term CMYK thrown around repeatedly. But what does it mean, how is it different from the colours on your screen, and why does it matter for your print job? Let's break it down.
What Does CMYK Stand For?
CMYK is the acronym for the four colours used in offset printing:
C = Cyan (light blue)
M = Magenta (red-pink)
Y = Yellow (bright yellow)
K = Key Black (black — 'K' is used instead of 'B' to avoid confusion with Blue)
These four colours, when printed in tiny overlapping dots, create the illusion of full-colour images. By varying the dot size and overlap of each colour, offset presses can produce virtually any colour imaginable — from skin tones to logos to photographic images.
How Offset Presses Print Colour
Offset printing is a halftone process. When you zoom in on a printed image under a magnifying glass, you will see thousands of tiny dots in various sizes. These dots — typically between 133 and 300 per inch (dpi) depending on the quality setting — are the building blocks of the image.
The press doesn't print solid colours. Instead, it uses four printing plates (one for each of C, M, Y, K) and layers these colours on top of each other. The printer controls the dot size and density of each colour to mix them and create new colours. This is called overprinting.
For example:
• 100% Cyan + 100% Yellow = Green
• 100% Magenta + 100% Yellow = Red
• 100% Cyan + 100% Magenta = Blue
• The combinations are endless.
CMYK vs RGB – The Critical Difference
| Aspect | RGB | CMYK |
|---|---|---|
| Where Used | Screen/digital (phones, computers, tablets) | Print (offset, digital printing) |
| Colour Mixing | Additive — adds light to create colours | Subtractive — removes light (absorbs ink) |
| Colour Range | Millions of colours available | Approximately 16,000 printable colours |
| Brightness | Bright and vibrant (light-based) | More muted (ink-based, no backlighting) |
This is critical: what you see on your screen (RGB) will not look exactly the same when printed (CMYK). RGB colours are created by light; CMYK colours are created by ink. Neon colours, bright blues, and vivid pinks often look more muted or different when printed, simply because the ink cannot reproduce the exact same colour range as light.
Why Designers Must Convert to CMYK Before Sending Files
If you send a file in RGB mode for offset printing, your print vendor will have to convert it. During conversion, colours can shift unpredictably. A bright turquoise on your screen might become a dull teal in print. A vibrant pink might look purple.
Always convert your file to CMYK before sending it to us. This gives you control over how colours will appear and helps us match your expectations.
Most professional design software (Adobe InDesign, Illustrator, Photoshop) allows you to preview how your RGB colours will look in CMYK before you even convert, using the 'Proof Setup' feature. Use this tool before finalising your design.
Pantone / Spot Colours in Offset Printing
For brand logos and critical colours, offset printing offers a fifth option: Pantone or Spot Colours.
Rather than relying on CMYK dot combinations, a spot colour uses a dedicated fifth ink plate to print that exact colour. This guarantees consistency and allows you to match brand colours precisely — essential if your company's logo must be an exact shade of blue or gold.
Spot colour printing adds cost (because it requires an extra printing plate) but is worth it for brand consistency, especially for products that will be printed repeatedly.
Common CMYK Mistakes and How to Avoid Them
Mistake 1: Rich Black. Never use 100% of all four colours (C:100 M:100 Y:100 K:100). This is called a '400% ink build' and causes wet sheets to stick together on the press. Instead, use 'Rich Black': C:60 M:40 Y:40 K:100. This gives you deep black without overloading the paper.
Mistake 2: Ignoring Total Ink Coverage. Keep total ink coverage under 320% across any pixel. Check your file's ink limit settings in your design software.
Mistake 3: Forgetting Bleed. Always add a 3–5mm bleed beyond your trim line. When offset presses cut sheets, they are not pixel-perfect — a small margin of error is unavoidable. Bleed ensures no white edges show up if the cut is slightly off.