With the latest release of LightSpace we have changed both the Rec709 and sRGB target profiles for Display Calibration.
This has been done for two different reasons.Rec709
has been changed to a pre-set Gamma target of 2.4 (previously 2.2).
This change has been made as the industry has slowly been moving to a gamma of 2.4 for Rec709, based on attempting to match the underlying 2.4 gamma for BT1886.
We do not necessarily agree with this, as on any display with a black level that is not close to zero BT1886 generates a system gamma that is closer to 2.2, rather than 2.4. But, the likes of the EBU have decided to ignore this fact, and have now specified a 2.4 gamma in EBU Tech 3320.
So, we have decided to follow this standard - as any user can adjust the Rec709 pre-set within LightSpace to any gamma target they want, and re-save as a new pre-set.sRGB
is a bit more interesting, as even we had this incorrect within LightSpace!
There is a misconception that the sRGB colour space standard has a compound gamma, with a linear portion close to black.
This is incorrect, as this is the sRGB Encoding
standard, not the target colour space standard for display calibration.
For display calibration the target colour space should use a simple power law gamma, 2.2.
This is the Encoding standard for sRGB: x <= 0.0031308 ? x * 12.92 : (1.055 * pow(x, 1/2.4)) - 0.055
(As defined in the IEC 61966-2-1:1999 Standard for sRGB.)
And this is the Encoding standard for Rec709: x < 0.018 ? (x * 4.5) : 1.099 * pow( x, (0.45) ) - 0.099
(As defined in the ITU-R Recommendation BT.709)
Both have a linear portion close to black, with different overall system gamma.
For display calibration it is incorrect to use these standards, and pure power law gamma should be used, as is now the standard colour space pre-sets within LightSpace.
Mob Boss at Light Illusion