---
title: "RGB versus CMY colour model"
subject: "Multimedia System"
chapter: 3
key: "semester_8/multimedia_system:rgb-vs-cmy"
source: https://www.bctengineer.com/q/semester_8/multimedia_system/rgb-vs-cmy
site: BCT Engineering
---

# RGB versus CMY colour model

Multimedia System · Chapter 3: Images and Graphics

- Asked in: 2074 Magh, 6 marks; 2072 Asoj, 7 marks; 2071 Bhadra, 6 marks (asked 3 times)
- Video: [RGB and CMY color model](https://www.youtube.com/watch?v=uhKFdhgF3xk) — kiran patil
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_8/multimedia_system/rgb-vs-cmy
- Whole chapter: https://www.bctengineer.com/md/semester_8/multimedia_system/chapter-3

## Question

Differentiate between the RGB colour model and the CMY colour model, with example.

## Short answer

RGB is additive, used in displays, combining red, green, blue light; CMY is subtractive, used in printing, combining cyan, magenta, yellow inks. They are complements: C=1-R, M=1-G, Y=1-B.

## Answer

**RGB** is an additive colour model that makes colours by adding red, green and blue light. **CMY** is a subtractive model that makes colours by removing (absorbing) parts of white light using cyan, magenta and yellow inks.

| Point | RGB | CMY |
|---|---|---|
| Full form | Red, Green, Blue | Cyan, Magenta, Yellow |
| Type | Additive | Subtractive |
| Based on | Light emitted by a source | Light reflected from a surface after absorption |
| Starting point | Black (no light) | White (paper) |
| All components at maximum | White | Black (in theory; real inks give dark brown) |
| All components zero | Black | White |
| Primary colours | R, G, B | C, M, Y |
| Secondary colours | Cyan, magenta, yellow | Red, green, blue |
| Used in | Monitors, TV, scanners, cameras, mobile screens | Printers, painting, photographic printing |
| Device type | Input and display devices | Output/hard-copy devices |

#### Relation between them

The two models are complements. With values normalised from 0 to 1:

C = 1 - R, M = 1 - G, Y = 1 - B

#### Example

- Pure red in RGB is (255, 0, 0), or (1, 0, 0) normalised. In CMY this is C = 1 - 1 = 0, M = 1 - 0 = 1, Y = 1 - 0 = 1, i.e. (0, 1, 1), or (0, 255, 255) on a 0-255 scale: magenta ink plus yellow ink absorb green and blue, leaving red.
- Yellow is (255, 255, 0) in RGB and (0, 0, 255) in CMY.
- White is (255, 255, 255) in RGB and (0, 0, 0) in CMY.

```text
 RGB (add light)          CMY (subtract light)
  R + G = Yellow           C + M = Blue
  G + B = Cyan             M + Y = Red
  R + B = Magenta          C + Y = Green
  R + G + B = White        C + M + Y = Black
```

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which statement correctly describes RGB and CMY?
   A. RGB is subtractive and CMY is additive
   B. Both are additive
   C. RGB is additive (adds light); CMY is subtractive (absorbs light)
   D. Both are subtractive
   Answer: C. RGB adds emitted light, CMY removes parts of white light with inks. (Key point: Additive vs subtractive)

2. Pure red is (255, 0, 0) in RGB. What is it in CMY?
   A. (0, 255, 255)
   B. (255, 0, 0)
   C. (255, 255, 0)
   D. (0, 0, 255)
   Answer: A. C = 1 - R = 0, M = 1 - G = 1, Y = 1 - B = 1, so (0, 255, 255). (Key point: Conversion)

3. What colour results when all components are at maximum in RGB and in CMY (theoretically)?
   A. Black in both
   B. White in both
   C. Black in RGB and white in CMY
   D. White in RGB and black in CMY
   Answer: D. R+G+B gives white light, while C+M+Y absorbs all light and gives black in theory. (Key point: Maximum components)

4. Where is each model mainly used?
   A. RGB for printers; CMY for monitors
   B. RGB for monitors, TV and scanners; CMY for printers
   C. Both only for printers
   D. Both only for monitors
   Answer: B. RGB suits light-emitting/input devices, CMY suits printing and hard-copy output. (Key point: Typical uses)

## Related in Multimedia System

- [Compare RGB, CMY and HSB models](https://www.bctengineer.com/question.md?key=semester_8%2Fmultimedia_system%3Argb-cmy-hsb-comparison) — Multimedia System, chapter 3
- [HSB versus YUV colour model](https://www.bctengineer.com/question.md?key=semester_8%2Fmultimedia_system%3Ahsb-vs-yuv) — Multimedia System, chapter 3, asked 2×
- [CMYK colour model and application](https://www.bctengineer.com/question.md?key=semester_8%2Fmultimedia_system%3Acmyk-colour-model) — Multimedia System, chapter 3

## Related in other subjects

- [Colour versus streak of mineral](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Acolour-versus-streak-of-mineral) — Engineering Geology I, chapter 3