// Workers AI · dad joke modeWhat did YJK say to its date? YJK-u later
YJK[1][2][3] is a proprietary color space implemented by the Yamaha V9958[4][5][6] graphic chip on MSX2+ computers.[7][8] It has the advantage of encoding images by implementing less resolution for color information than for brightness, taking advantage of the human visual systems' lower acuity for color differences.[9] This saves memory, transmission and computing power.
YJK is composed of three components: , and . is similar to luminance (but computed differently), and are the chrominance components (representing red and green color differences).
The component is a 5-bit unsigned value (0 to 31), specified for each individual pixel. The and components are stored together in 6 bits as a complement signed value (-32 to 31) and shared between 4 adjacent horizontal pixels (4:1:1 chroma sub-sampling).[10][11][12]
The following table shows the encoding of this information across 4 pixels:[10]
| Pixel coordinates | Bits | |||||||
|---|---|---|---|---|---|---|---|---|
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |
| 0,0 | Y1 | K low | ||||||
| 0,1 | Y2 | K high | ||||||
| 0,2 | Y3 | J low | ||||||
| 0,3 | Y4 | J high | ||||||
This arrangement allows for the encoding of 19,268 different colors.[10][11][12] While conceptually similar to YUV, chroma sampling, numerical relationship between the components, and transformation to and from RGB are different in YJK.
Formulas
[edit]
The three component signals are created from an original RGB (red, green and blue) source. The weighted values of , and are added together to produce a single signal, representing the overall brightness of that pixel. The signal is then created by subtracting the from the red signal of the original RGB, and then scaling; and by subtracting the from the green, and then scaling by a different factor.
These formulae approximate the conversion between the RGB color space and YJK:[7]
From RGB to YJK:
From YJK to RGB:
The component of YJK is not true luminance, since the green component has less weight than the blue component.[2] Also, contrary to YUV where chrominance is based on Red-Blue differences, on YJK its calculated based on Red-Green differences.[10]
References
[edit]- ↑ Holst, Laurens (2022). "The YJK screen modes". MSX Assembly Page.
- 1 2 Niemietz, Ricardo Cancho (2014). Issues on YJK colour model implemented in Yamaha V9958 VDP chip (PDF).
- ↑ "VCFe Vortrag vom 2016.04.30 - Homecomputer und Spielkonsolen - Videoarchitekturen als visuelles Medium". neil.franklin.ch. Retrieved 2022-11-13.
- ↑ IC Master. Vol. 3. Hearst Business Communications, 2001. 2001.
- ↑ Martín Sesma, Sergio (2016-10-03). Arqueología informática: los ordenadores MSX en los inicios de la microinformática doméstica (Proyecto/Trabajo fin de carrera/grado thesis). Universitat Politècnica de València. hdl:10251/70909.
- ↑ Redazione (2008-10-20). "MSX - Vari Costruttori- 1983". CyberLudus.com (in Italian). Retrieved 2022-11-13.
- 1 2 "V9958 MSX-VIDEO TECHNICAL DATA BOOK" (PDF). 1988.
- ↑ Alex, Wulms (1995). "Schermen op MSX - De 2+ schermen" (PDF). MSX Computer & Club Magazine (72).
- ↑ S. Winkler, C. J. van den Branden Lambrecht, and M. Kunt (2001). "Vision and Video: Models and Applications". In Christian J. van den Branden Lambrecht (ed.). Vision models and applications to image and video processing. Springer. p. 209. ISBN 978-0-7923-7422-0.
{{cite book}}: CS1 maint: multiple names: authors list (link) - 1 2 3 4 5 Grauw (2026). "The YJK screen modes". MSX Assembly Page.
- 1 2 Silveira, Marcelo (2017). MSX 2+ Colors (PDF). MarMSX - Development page.
- 1 2 Nunes, Giovanni (8 June 2015). "Edição de imagens num MSX2+/MSX turbo R". Retrópolis - A cidade dos clássicos.
