YJK

The three component signals are created from an original RGB (red, green and blue) source. The weighted values of ${\displaystyle R}$, ${\displaystyle G}$ and ${\displaystyle B}$ are added together to produce a single ${\displaystyle Y}$ signal, representing the overall brightness of that pixel. The ${\displaystyle J}$ signal is then created by subtracting the ${\displaystyle Y}$ from the red signal of the original RGB, and then scaling; and ${\displaystyle K}$ by subtracting the ${\displaystyle Y}$ 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:

${\displaystyle Y=B/2+R/4+G/8}$

${\displaystyle J=R-Y}$

${\displaystyle K=G-Y}$

From YJK to RGB:

${\displaystyle R=Y+J}$

${\displaystyle G=Y+K}$

${\displaystyle B=(5/4)Y-J/2-K/4}$

The ${\displaystyle Y}$ 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]

• YUV
• MSX2+