Encyclopedia

SYCC

Color space

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Source updated December 23, 2025

sYCC is a standard numerical encoding of colors, similar to the CIE YCbCr encoding, It uses three coordinates: a luma value $Y$ , that is roughly proportional to perceived brightness of the color, and two chroma values $C_{b}$ and $C_{r}$ , which are roughly the "blueness" and "redness" of the hue. Each coordinate is represented by an integer with some number $N$ of bits, which is interpreted as either unsigned (for $Y$ ) or signed (for $C_{b}$ and $C_{r}$ ).

The space is defined by Annex F of the International Electrotechnical Commission (IEC) standard 61966-2-1 Amendment 1 (2003), as a linear transformation of the non-linear sRGB color space defined by the same document.

The official conversion from sYCC to sRGB will often result in negative R, G, or B values or values greater than 1 but unlike in normal YCbCr those values are not clamped. The same for when XYZ is converted into sYCC values, at the sRGB stage negative and greater than 1 values are preserved. The sRGB transfer function is thus modified to accept negative RGB values.

01sYCC definition

The three unsigned integers $Y,C_{b},C_{r}$ of an sYCC encoded color represent fractional coordinates $Y',C_{b}',C_{r}'$ according to the formulas

$Y'=Y/M$

$C_{b}'=(C_{b}-Z)/M$

$C'_{r}=(C_{b}-Z)/M$

where the scale factor $M=2^{N}-1$ is the maximum unsigned $N$ -bit integer, and the offset $Z$ is $2^{N-1}$ (as in the usual two's complement representation of signed integers). Conversely, the encoded integer values are given by

$Y={\mbox{round}}(MY')$

$C_{b}={\mbox{round}}(Z+MC_{b}')$

$C_{r}={\mbox{round}}(Z+MC_{r}')$

with the resulting values clipped to the range $0..M$ .

In particular, for $N=8$ (which is the normal bit size), one gets $M=255$ and $Z=128$ . Thus the fractional luma $Y'$ ranges from 0 to 1, while the fractional chroma coordinates range from $-128/255\approx -0.50196...$ to $+127/255\approx +0.498039...$ .

The standard specifies that these fractional values $Y',C_{b}',C_{r}'$ are related to the non-linear fractional sRGB coordinates $R',G',B'$ by a linear transformation, described by the matrix product

${\begin{bmatrix}Y'\\C_{b}'\\C_{r}'\end{bmatrix}}={\begin{bmatrix}+0.2990&+0.5870&+0.1140\\-0.1687&-0.3313&+0.5000\\+0.5000&-0.4187&-0.0813\end{bmatrix}}{\begin{bmatrix}R'\\G'\\B'\end{bmatrix}}$

This correspondence is the same as the RGB to YCC mapping specified by the old TV standard ITU-R BT.601-5, note that the coefficients of $Y'$ here are defined still with 3 decimal places, because 4 decimal places would change legacy encoding of images (first row: Kr = 0.299 and Kg = 0.587).

The non-linear fractional sRGB coordinates $R',G',B'$ can be computed from the fractional sYCC coordinates $Y',C_{b}',C_{r}'$ by inverting the above matrix. The standard gives the approximation

${\begin{bmatrix}R'\\G'\\B'\end{bmatrix}}={\begin{bmatrix}+1.0000&0.0000&+1.4020\\+1.0000&-0.3441&-0.7141\\+1.0000&+1.7720&0.0000\end{bmatrix}}{\begin{bmatrix}Y'\\C_{b}'\\C_{r}'\end{bmatrix}}$

which is expected to be accurate enough for $N=8$ bits per component. For bit sizes greater than 8, the standard recommends using a more accurate inverse. It states that the following matrix with 6 decimal digits is accurate enough for $N=16$ :

${\begin{bmatrix}R'\\G'\\B'\end{bmatrix}}={\begin{bmatrix}+1.000000&+0.000037&+1.401988\\+1.000000&-0.344113&-0.714104\\+1.000000&+1.771978&+0.000135\end{bmatrix}}{\begin{bmatrix}Y'\\C_{b}'\\C_{r}'\end{bmatrix}}$

The same standard specifies the relation between the non-linear fractional coordinates $R',G',B'$ and the CIE 1931 XYZ coordinates. The connection entails the transfer function ("gamma correction") that maps $R',G',B'$ to the linear R, G, B coordinates, and then a 3D linear transformation that relates these to the CIE $X,Y,Z$ .

Since the linear transformation from sRGB to sYCC is defined in terms of non-linear (gamma-encoded) values ( $R',G',B'$ ), rather than the linear ones ( $R,G,B$ ), the $Y'$ component of sYCC is not the CIE Y coordinate, not even a function of it alone. That is, two colors with the same CIE Y value may have different sYCC $Y'$ values, and vice-versa.

Particular values

The integer encoded sYCC triplet $(0,0,0)$ represents the color black whereas $(255,0,0)$ is white (more precisely, the CIE illuminant D65). More generally, triplets $(Y,0,0)$ , for $Y$ in 0..255, represent shades of gray.

Note that the 8-bit integer sYCC triplet $(Y,Cb,Cr)=(0,255,255)$ has fractional coordinates $(Y',Cb',Cr')\approx (0.0,0.5,0.5)$ , which, according to these matrices, has fractional non-linear sRGB coordinate $G'\approx -0.5\times (0.3341+0.7141)\approx -0.528$ , and therefore has to be converted to XYZ to be realizable or perceivable. Similarly, the sYCC triplet $(0,0,0)$ has $R'\approx -0.701$ and $B'\approx -0.886$ .

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Sources and credits

This article is adapted from the Wikipedia article “SYCC”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.

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