--- title: "CMYK colour model and application" subject: "Multimedia System" chapter: 3 key: "semester_8/multimedia_system:cmyk-colour-model" source: https://www.bctengineer.com/q/semester_8/multimedia_system/cmyk-colour-model site: BCT Engineering --- # CMYK colour model and application Multimedia System · Chapter 3: Images and Graphics - Asked in: 2074 Bhadra, 3+3+5 marks - Video: [CMYK color model || Multimedia Technology](https://www.youtube.com/watch?v=HhN9q81TDIY) — Institute Academy - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/multimedia_system/cmyk-colour-model - Whole chapter: https://www.bctengineer.com/md/semester_8/multimedia_system/chapter-3 ## Question Different colour models are often used in different applications. What is the CMYK colour model? Give an application in which this colour model is mostly used and explain the reason. ## Short answer CMYK is a subtractive colour model with cyan, magenta, yellow and black inks for printing. It is used in colour printing because paper reflects light requiring subtractive mixing; black ink provides true black, saves cost and speeds drying. ## Answer #### CMYK colour model **CMYK** stands for Cyan, Magenta, Yellow and Key (black). It is a **subtractive** colour model used for printing. Each ink absorbs (subtracts) some of the light falling on white paper, and the colour seen is the light that is reflected back. - Cyan absorbs red, magenta absorbs green, yellow absorbs blue. - Each component is a percentage from 0 to 100% of ink coverage. For example (0, 100, 100, 0) is red, and (0,0,0,100) is pure black. - Conversion from RGB (values 0-1): K = 1 - max(R,G,B), C = (1 - R - K)/(1 - K), M = (1 - G - K)/(1 - K), Y = (1 - B - K)/(1 - K). The fourth channel K (black) is added because C + M + Y inks together do not make a true black in practice; they give a muddy dark brown. ```text C + M = Blue C + Y = Green M + Y = Red C + M + Y = dark brown -> K ink added for true black ``` #### Application: colour printing CMYK is mostly used in **commercial and desktop colour printing**: magazines, newspapers, books, posters, packaging and inkjet/laser colour printers. Images designed on screen in RGB are converted to CMYK before going to the press. #### Reason for use in printing 1. **Printing is subtractive.** Paper does not emit light; it reflects ambient light, so inks must subtract colours from white, which is exactly what CMY does. RGB (additive light) cannot be used with ink on paper. 2. **True black and sharp text.** A separate black ink gives deep black and crisp small text without registration problems of three overlapping inks. 3. **Saves cost and drying time.** Using one black ink in place of equal amounts of C, M and Y saves expensive coloured ink, and less ink makes the paper dry faster and avoids soaking. 4. **Better grey and shadow control** and a wide range of printable colours with only four plates, one plate for each ink. A limit is that the CMYK gamut is smaller than RGB, so very bright screen colours (vivid green or blue) look duller in print. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why is a separate black (K) ink added to CMY? A. Because cyan, magenta and yellow cannot make any colour B. Because K increases the colour gamut beyond RGB C. Because C + M + Y inks give a muddy dark brown, not true black D. Because paper emits light that must be blocked Answer: C. In practice equal C, M and Y do not give true black, so a separate K ink gives deep black and crisp text. (Key point: Why K is added) 2. Why is CMYK, not RGB, used for ink on paper? A. Paper emits light, so inks add colour to it B. Paper only reflects ambient light, so inks must subtract colours from white C. RGB inks are too expensive D. RGB cannot show black Answer: B. Printing is subtractive: each ink absorbs part of the light on white paper and the reflected light is the colour seen. (Key point: Subtractive principle) 3. Which ink absorbs which colour of light? A. Cyan absorbs green, magenta absorbs blue, yellow absorbs red B. Cyan absorbs blue, magenta absorbs red, yellow absorbs green C. Cyan absorbs red, magenta absorbs green, yellow absorbs blue D. All three absorb all colours equally Answer: C. Each ink is the complement of an RGB primary: cyan removes red, magenta removes green, yellow removes blue. (Key point: Ink absorption) 4. What is a limit of CMYK when moving an image from screen to print? A. Its gamut is smaller than RGB, so vivid screen colours look duller in print B. It can show only 256 colours C. It cannot print text D. It needs more ink for black Answer: A. Some bright RGB colours (vivid green or blue) cannot be printed in CMYK and appear duller. (Key point: Limitation) ## Related in Multimedia System - [RGB versus CMY colour model](https://www.bctengineer.com/question.md?key=semester_8%2Fmultimedia_system%3Argb-vs-cmy) — Multimedia System, chapter 3, asked 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× - [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 ## Related in other subjects - [Compare software models; propose a fourth model](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Asw-models-compare-fourth) — Instrumentation II, chapter 9 - [Software process models and effort estimation](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Asw-process-models) — Instrumentation II, chapter 9, asked 2× - [Types of models in OOAD](https://www.bctengineer.com/question.md?key=semester_6%2Fobject_oriented_analysis_and_design%3Atypes-of-models-in-ooad) — Object Oriented Analysis and Design, chapter 1 - [VHDL models; full adder structural](https://www.bctengineer.com/question.md?key=semester_6%2Fembedded_system%3Avhdl-models-full-adder-structural) — Embedded System, chapter 9