ScRGB color space
Encyclopedia
scRGB is a wide color gamut
RGB (Red Green Blue) 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 without the complexity of color management
. The cost of maintaining compatibility with sRGB is that approximately 80% of the scRGB color space consists of imaginary color
s.
Large positive numbers allow high dynamic range
images to be represented, though the range is inferior to that of some other high dynamic range formats such as OpenEXR
.
The 16 bit scRGB(16) encoding is the linear RGB channels converted by
. Compared to 8-bit sRGB this ranges from about 1/2 the color resolution near 0.0 to more than 10 times the color resolution near 1.0. Storage as 16 bits clamps the linear range to 
.
The 12-bit scRGB-nl encoding is the linear RGB channels passed through the same gamma function as sRGB (for negative numbers use -f(-x)) and then converted by
. This is exactly 5 times the color resolution of 8-bit sRGB, and 8-bit sRGB can be converted directly with 
. The linear range is clamped to the slightly larger 
A 12-bit encoding called scYCC-nl is the conversion of the non-linear sRGB levels to JFIF-Y'CbCr
and then converted by
and 
. 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
where 
is 12 or 16.
. 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.
Gamut
In color reproduction, including computer graphics and photography, the gamut, or color gamut , is a certain complete subset of colors. The most common usage refers to the subset of colors which can be accurately represented in a given circumstance, such as within a given color space or by a...
RGB (Red Green Blue) color space created by Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
and HP
Hewlett-Packard
Hewlett-Packard Company or HP is an American multinational information technology corporation headquartered in Palo Alto, California, USA that provides products, technologies, softwares, solutions and services to consumers, small- and medium-sized businesses and large enterprises, including...
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
CIE 1931 color space
In the study of color perception, one of the first mathematically defined color spaces is the CIE 1931 XYZ color space, created by the International Commission on Illumination in 1931....
while maintaining simplicity and backward compatibility with sRGB without the complexity of color management
Color management
In digital imaging systems, color management is the controlled conversion between the color representations of various devices, such as image scanners, digital cameras, monitors, TV screens, film printers, computer printers, offset presses, and corresponding media.The primary goal of color...
. The cost of maintaining compatibility with sRGB is that approximately 80% of the scRGB color space consists of imaginary color
Imaginary color
Non-physical, unrealizable, or imaginary colors are points in a color space that correspond to combinations of cone cell responses that cannot be produced by any physical light spectrum. Thus, no object can have an imaginary color, and imaginary colors cannot be seen under normal circumstances...
s.
Large positive numbers allow high dynamic range
High dynamic range
High dynamic range is a term generally used for media applications such as digital imaging and digital audio production...
images to be represented, though the range is inferior to that of some other high dynamic range formats such as OpenEXR
OpenEXR
OpenEXR is a high dynamic range imaging image file format, released as an open standard along with a set of software tools created by Industrial Light and Magic , released under a free software license similar to the BSD license....
.
Encoding
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
. Compared to 8-bit sRGB this ranges from about 1/2 the color resolution near 0.0 to more than 10 times the color resolution near 1.0. Storage as 16 bits clamps the linear range to .The 12-bit scRGB-nl encoding is the linear RGB channels passed through the same gamma function as sRGB (for negative numbers use -f(-x)) and then converted by
. This is exactly 5 times the color resolution of 8-bit sRGB, and 8-bit sRGB can be converted directly with . The linear range is clamped to the slightly larger A 12-bit encoding called scYCC-nl is the conversion of the non-linear sRGB levels to JFIF-Y'CbCr
YCbCr
YCbCr or Y′CbCr, sometimes written or , is a family of color spaces used as a part of the color image pipeline in video and digital photography systems. Y′ is the luma component and CB and CR are the blue-difference and red-difference chroma components...
and then converted by
and . This form can allow greater compression and direct conversion to/from JPEGJPEG
In computing, JPEG . The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality....
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
where is 12 or 16.Usage
The first implementation of scRGB was the GDI+ API in Windows VistaWindows Vista
Windows Vista is an operating system released in several variations developed by Microsoft for use on personal computers, including home and business desktops, laptops, tablet PCs, and media center PCs...
. At WinHEC
Windows Hardware Engineering Conference
The Windows Hardware Engineering Conference is the annual software and hardware developer-oriented trade show and business conference where Microsoft elaborates on its hardware plans for Microsoft Windows-compatible PCs...
2008 Microsoft announced that Windows 7 would support 48-bit scRGB (which for HDMI
High-Definition Multimedia Interface
HDMI is a compact audio/video interface for transmitting uncompressed digital data. It is a digital alternative to consumer analog standards, such as radio frequency coaxial cable, composite video, S-Video, SCART, component video, D-Terminal, or VGA...
can be converted and output as xvYCC
XvYCC
xvYCC or Extended-gamut YCC is a color space that can be used in the video electronics of television sets to support a gamut 1.8 times as large as that of the sRGB color space...
). The components in Windows 7 that support 48-bit scRGB are Direct3D
Direct3D
Direct3D is part of Microsoft's DirectX application programming interface . Direct3D is available for Microsoft Windows operating systems , and for other platforms through the open source software Wine. It is the base for the graphics API on the Xbox and Xbox 360 console systems...
, the Windows Imaging Component
Windows Imaging Component
The Windows Imaging Component is a Component Object Model based imaging codec framework introduced in Windows Vista and Windows XP Service Pack 3 for working with and processing digital images and image metadata...
, and the Windows Color System
Windows Color System
Windows Color System is a platform for color management first included with Windows Vista that aims to achieve color consistency across various software and hardware, including cameras, monitors, printers and scanners. Different devices interpret the same colors differently, according to their...
and they support it in both full screen exclusive mode and in video overlays.
External links
- The standard IEC 61966-2-2
- Annex B: Non-linear encoding for scRGB : scRGB-nl
- A working draft of IEC 61966-2-2 is available online.
- ExtremeTech: Defining scRGB