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ScRGB
ScRGB
ScRGB
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scRGB
IEC 61966-2-2:2003
Intersection of the scRGB gamut with the X+Y+Z=.6443 plane (the gamut varies depending on the intensity as it is a cube with a non-zero origin).
Native name
  • scRGB
  • IEC 61966-2-2:2003
StatusPublished
First publishedJanuary 23, 2003; 22 years ago (2003-01-23)[1]
Organization
CommitteeTC/SC: TC 100/TA 2
Authors
Base standardssRGB
Related standardsAdobe RGB color space
DomainColor space, color model

scRGB is a wide color gamut RGB color space created by Microsoft and HP that uses the same color primaries and white/black points as the sRGB color space but allows coordinates below zero and greater than one. The full range is −0.5 through just less than +7.5.

Negative numbers enables scRGB to encompass most of the CIE 1931 color space while maintaining simplicity and backward compatibility with sRGB by not changing the primary colors. However this means approximately 80% of the scRGB color space consists of imaginary colors. Numbers greater than 1.0 allow high dynamic range images to be represented, though the dynamic range is less than other formats.[2]

Encoding

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Two encodings are defined for the individual primaries: a linear 16 bit per channel encoding and a nonlinear 12 bit per channel encoding.

The 16 bit scRGB(16) encoding is the linear RGB channels converted by 8192x + 4096. Compared to 8-bit sRGB this ranges from almost 2+1⁄2 times the color resolution near 0.0 to more than 14 times the color resolution near 1.0. Storage as 16 bits clamps the linear range to −0.5..7.4999.

The 12-bit scRGB-nl encoding is the linear RGB channels passed through the same opto-electric conversion function as sRGB (for negative numbers use −f(−x)) and then converted by 1280x + 1024. This is exactly 5 times the color resolution of 8-bit sRGB, and 8-bit sRGB can be converted directly with 5x + 1024. The linear range is clamped to the slightly larger −0.6038..7.5913.

A 12-bit encoding called scYCC-nl is the conversion of the non-linear sRGB levels to JFIF-Y'CbCr and then converted by 1280Y′ + 1024, 1280Cb + 2048, 1280Cr + 2048. This form can allow greater compression and direct conversion to/from JPEG files and video hardware.

With the addition of an alpha channel with the same number of bits the 16-bit encoding may be seen referred to as 64 bit and the 12-bit encoding referred to as 48-bit. Alpha is not encoded as above, however. Alpha is instead a linear 0-1 range multiplied by 2n − 1 where n is 12 or 16.

The much newer DXGI scRGB HDR swapchains store the linear sRGB channels as 16-bit half float and has a much larger range of over ±60,000, without any enforced clamps.[citation needed] Storing linear sRGB values as floating point is very common in modern computer graphics software.

Usage

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The first implementation of scRGB was the GDI+ API in Windows Vista. At WinHEC 2008 Microsoft announced that Windows 7 would support 48-bit scRGB (which for HDMI can be converted and output as xvYCC). The components in Windows 7 that support 48-bit scRGB are Direct3D, the Windows Imaging Component, and the Windows Color System and they support it in both full screen exclusive mode and in video overlays.[3][4]

Origin of sc in scRGB

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The origin of the sc in scRGB is shrouded in mystery. Officially it stands for nothing. According to Michael Stokes (the national and international leader of the International Electrotechnical Commission, or IEC, group working on scRGB), the name appeared when the Japanese national committee requested a name change from the earlier XsRGB (excess RGB). The two leading candidates for meaning are "specular RGB" because scRGB supports whites greater than the diffuse 1.0 values, and "standard compositing RGB" because the linearity, floating-point support, HDR (high dynamic range) support, and wide gamut support are ideally suited for compositing. This meaning also implicitly emphasizes that scRGB is not intended to be directly supported in devices or formats, since by definition scRGB encompasses values that are beyond both the human visual system and (even theoretically) realizable physical devices.[5]

References

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ScRGB

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scRGB is a colorimetric RGB color space with an extended and , standardized by the (IEC) in its 2003 publication IEC 61966-2-2 as an extension of the color space for use in systems and equipment. It features linear encoding of light levels, shares the same primaries (defined by x, y coordinates: red at 0.64, 0.33; green at 0.30, 0.60; blue at 0.15, 0.06) and D65 as , and supports 16-bit per channel encoding with values ranging from -0.5 to approximately 7.5 to represent relative scene radiance, including sub-black details and specular highlights beyond white. This design ensures with while enabling high-fidelity color reproduction for wide content. Developed in the context of advancing for and displays, scRGB addresses limitations in by accommodating a broader range of visible colors and levels, making it suitable for encoding, editing, and communicating scene-referred data in applications like graphics rendering, , and . The space is scene-referred rather than display-referred, emphasizing accurate capture of real-world lighting conditions over device-specific output. In practice, scRGB has been adopted in key platforms, including Microsoft's Windows ecosystem—where it supports (HDR) workflows in for advanced color spaces and in Windows Presentation Foundation (WPF) for color structure handling—and Android's system for linear, sRGB-compatible processing. Its integration facilitates seamless color exchange across devices, though practical implementation often involves transformations to handle the extended range, such as clamping or for standard displays.

Overview

Definition and Purpose

scRGB is a wide color gamut RGB color space developed by Microsoft and Hewlett-Packard as an extension of the standard. It employs the same color primaries and white and black points as but features an extended linear value range for each channel from -0.5 to approximately +7.5. This design, formalized in the international standard IEC 61966-2-2, supports 16 bits per channel in linear encoding (48 bits per pixel total) or 12 bits per channel with nonlinear encoding (36 bits per pixel). The primary purpose of scRGB is to enable the encoding, editing, and communication of images with wide , extended color gamut, and higher bit depth, facilitating more accurate representation of scene radiance in workflows. By allowing values below 0 and above 1.0, it supports (HDR) content, capturing brighter highlights and deeper shadows while permitting the representation of the entire visible color —and even some mathematically defined "imaginary" colors outside physical realizability through negative primaries. This makes scRGB particularly suitable for applications in , , and advanced display rendering where enhanced color fidelity and range are essential. scRGB maintains backward compatibility with sRGB by directly mapping content within the 0 to 1.0 value range without alteration, ensuring that standard images can be processed seamlessly within the scRGB framework.

Relation to sRGB

scRGB inherits the RGB primaries, , and black point directly from , ensuring perceptual consistency for standard colors. The primaries are defined as at chromaticity coordinates (x=0.64, y=0.33), at (x=0.30, y=0.60), and at (x=0.15, y=0.06), with the at D65 (x=0.3127, y=0.3290) and black at (0,0,0). In contrast to sRGB's nonlinear gamma encoding, scRGB employs linear light values, which permit negative components to represent undersaturated colors below and values exceeding 1 to capture supersaturated or high-luminance colors beyond . This linearity facilitates computational operations in graphics pipelines, such as blending and lighting, without the distortions introduced by sRGB's . The shared primaries and enable , allowing linear equivalents of content in the 0-1 range—derived via gamma decoding—to map directly into scRGB without requiring or primary matrix transformations, thus supporting seamless integration of standard material into extended workflows. By eschewing 's 8-bit gamma-encoded limitations, which clip wide-gamut colors and data to prevent overflow, scRGB's linear approach and expanded precision preserve such information, enabling more accurate representation in applications demanding broader color volumes.

Technical Specifications

Color Primaries and White Point

scRGB defines its color basis using the same primaries and as the color space, ensuring compatibility with established RGB workflows. The RGB primaries are specified by their CIE 1931 coordinates as follows: at (x=0.64, y=0.33, z=0.03), at (x=0.30, y=0.60, z=0.10), and blue at (x=0.15, y=0.06, z=0.79). These coordinates, derived from the BT.709 primaries, form the vertices of the triangle in the CIE xy . The white point is the CIE D65, with coordinates (x=0.3127, y=0.3290, z=0.3583), approximating average daylight conditions. This white point provides a neutral reference for color balancing and ensures consistent rendering across display environments. The black point is assumed to be at the origin (0,0,0) in CIE XYZ tristimulus values, representing the absence of light without a specified offset. To convert scRGB values to CIE XYZ tristimulus values, a 3x3 is applied to the linear RGB components. This matrix, identical to that of , is: (XYZ)=(0.41240.35760.18050.21260.71520.07220.01930.11920.9505)(RGB)\begin{pmatrix} X \\ Y \\ Z \end{pmatrix} = \begin{pmatrix} 0.4124 & 0.3576 & 0.1805 \\ 0.2126 & 0.7152 & 0.0722 \\ 0.0193 & 0.1192 & 0.9505 \end{pmatrix} \begin{pmatrix} R \\ G \\ B \end{pmatrix}
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