SRGB Color Space
Thomas Sapiano and Pro Photo Wiki Contributors
Introduction
The sRGB colour space (officially defined as IEC 61966-2-1:1999) was created by HP and Microsoft to provide a standard working space for personal computers. As sRGB was intended to provide a common baseline, it is designed around the viewing conditions experienced by a mainstream computer user. In theory, this means that when sRGB images are displayed in programs that are
not ICC-aware they will still appear reasonably correct on a typical monitor. As such, sRGB is commonly used in situations (such as websites) where images will be viewed in uncontrolled environments.
Currently, sRGB is used as the default colour space for many image formats, and is the assumed colour space in modern versions of Microsoft Windows. Most digital cameras can be configured to shoot images in sRGB, and many other imaging devices have similar options. Due to this prevalence, many commercial printers have been optimized to work around the sRGB colour space as well.
[
edit]
Alternatives
As sRGB was designed around mainstream viewing conditions, it provides a smaller
gamut (range of colours) than many other commonly used colour spaces. While these additional colours often can't be reproduced by consumer-oriented imaging equipment, they may be important for reproduction in high-end environments. As such, larger spaces like
AdobeRGB or
scRGB may be more suitable for certain professional applications. Note, however, that images produced in these larger colour spaces must remain within a controlled workflow for proper reproduction.
[
edit]
Technical Details
[
edit]
Gamut
The range of colours that can be represented within the sRGB space have been intentionally designed to reflect those that can be reproduced by common computer monitors. As sRGB was designed in the late 1990s, this
gamut is modeled around CRT displays that were available at the time.
While sRGB can only contain a small subset of the colours that the human eye can percieve, most of the colours that fall outside of it's range cannot be reproduced by consumer output devices. Certain high-end devices can generate some of these colours, however, so some photographers may elect to use a larger colour space such as
AdobeRGB to store their images in.
[
edit]
Primaries
Normally, the red, green and blue values used to store colour within an uncalibrated image file are dependant on the device that is producing them. Working colour spaces like sRGB are designed to standardize these values, so that those device-specific values can be converted into a standard method of describing colour. As such, within the context of any colour space, the actual
primary colours in use must be defined in an objective manner. This is done by specifying the CIE xy chromaticity coordinates for each of the
primaries used within that space. The following table provides the values defined for the sRGB colour space:
| Primary | x | y |
|---|
| Red | 0.6400 | 0.3300 |
| Green | 0.3000 | 0.6000 |
| Blue | 0.1500 | 0.0600 |
Please see
this article for more detailed information on this topic, as further discussion is beyond the scope of this article.
[
edit]
Gamma
As the human eye perceives light in an exponential manner, most colour spaces apply a
gamma correction to the linear image data captured by the camera. As sRGB was designed to reflect the performance of a typical CRT monitor, it uses a
gamma value of 2.2 across most of the tonal range.
Strictly speaking, the sRGB standard defines this transform using a more complicated set of formulae. While the gamma 2.2 curve closely matches the results of this transform, there is some variation in the deep shadows. The official definition of this transform is as follows:
- If Nlinear <= 0.00304, Nsrgb = 12.92*Nlinear
- If Nlinear > 0.00304, Nsrgb = (1.055)*Nlinear1/2.4 - 0.055
Where N
linear and N
srgb are the normalized linear and corrected (respectively) values of an R, G or B channel.
[
edit]
See Also- AdobeRGB - Colour space commonly used in professional enviroments that require a larger colour gamut.
- ProPhotoRGB - Large colour space for uses in situations where AdobeRGB is insufficient.
- scRGB - New colour space designed for use with high bit-depth imaging.
[
edit]
External Links 
Linear Mode
