Anyone specifying a corporate colour quickly encounters a problem: on screen the blue shines brilliantly (RGB), in offset printing it looks dull (CMYK), and for signage or paintwork a RAL or HKS number is needed. The professional colour converter translates between all relevant colour systems and simultaneously shows where the physical limits of colour reproduction lie.
Step by Step: How to Use the Professional Colour Converter
- Select the source colour space: RGB for screen/web (0–255 per channel), HEX for CSS/HTML (#RRGGBB), CMYK for print preparation (0–100% per channel), LAB for device-independent colour communication.
- Enter the colour values: For RGB e.g. R:0 G:82 B:155 (a typical corporate blue). For HEX: #00529B. The calculator immediately computes all other representations.
- Use CMYK values for print preparation: The CMYK values shown are approximations; for professional printing always use an ICC colour profile (e.g. ISOcoated_v2) in InDesign or Photoshop.
- Check spot colours: Pantone, HKS, and RAL have fixed ink recipes. The calculator shows the nearest spot colour — but no exact mathematical conversion exists. The match must always be verified visually.
- Use LAB values for colour accuracy: LAB (CIE L*a*b*) is device-independent. Colour difference ΔE < 1: barely visible; ΔE 1–3: a trained observer can see the difference; ΔE > 3: clearly visible.
Practical Examples
Example 1 – Corporate design blue: Web design delivers #0055A4 (RGB 0/85/164). CMYK calculation: C = 1−0/255 = 1.00 (100%); M = 1−85/255 = 0.667 (67%); Y = 0; K = 0. Nearest Pantone equivalent in print: Pantone 2945 C — must be confirmed visually.
Example 2 – RAL for paintwork: A machine housing is to be painted in a grey tone that matches the company logo (RGB 128/128/128). Nearest RAL: RAL 7040 Window Grey. CMYK 0/0/0/50 in print gives a similar grey, but never exactly the same.
Example 3 – Gamut problem with vivid orange: Marketing wants orange RGB 255/80/0 for a brochure. CMYK: C=0/M=69/Y=100/K=0. This orange lies outside the ISO CMYK gamut — the print result will be noticeably flatter. Solution: use Pantone 151 as a spot colour channel, or adjust expectations for print colours.
Professional Colour Conversion: RGB, CMYK, HEX, LAB
RGB → CMYK: C=1-(R/255); M=1-(G/255); Y=1-(B/255); K=min(C,M,Y). Important: screen colours (RGB) cannot be transferred 1:1 to print colours (CMYK)! Spot colours (Pantone, HKS, RAL) have fixed ink recipes that must be matched visually.
Frequently Asked Questions (FAQ)
Why does printed colour look different from the screen?
Screens emit light (additive RGB); printing inks absorb light (subtractive CMYK). The RGB colour space is significantly larger than the CMYK gamut — vivid colours such as neon green, strong blue, or pure red simply cannot be reproduced in offset printing.
What is the difference between HKS and Pantone?
HKS is a spot colour system developed in Germany with 88 base colours (originally for reel-fed printing). Pantone is the globally dominant US system with over 1,800 colours. HKS is particularly common in the German print market for magazines and forms; internationally, Pantone is standard.
What does ΔE mean and how large can it be?
ΔE (delta E) measures the perceptible colour difference in the LAB colour space. ΔE < 1 is imperceptible to humans; ΔE 2–3 is accepted by professionals as the tolerance limit for colour consistency in printing; ΔE > 5 is clearly visible to any observer. The ISO standard for offset printing (ISO 12647) permits ΔE ≤ 5.
