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Confusion over display calibration being subtractive

 
Author Steve

INF
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#1 | Posted: 8 Oct 2021 10:09 | Edited by: Steve 
It is often stated that all display calibration is subtractive, which is true.
Calibration cannot increase what isn't already there.
This means no calibration, manual or LUT based, can make a display's peak white brighter than the maximum the display can do, nor make black blacker.
Similarly, no calibration, manual or LUT based, can make the gamut wider than the maximum the display can natively achieve.

Additionally, LUT based calibration cannot undo clipping in the blacks or whites - manual adjustment is required for that, pre application of any LUT.

But, what can be seen from the above is the limitation is always at the extremes of the display's capabilities.
It's maximum white; minimum black, maximum gamut.

Within those extremes, calibration, both manual and LUT based, can make adjustments in any direction, until the extremes of the display's capabilities are reached.
That mean gamut (colour/saturation) can be increased, within the maximum gamut capabilities of the display.
And brightness (so EOTF/gamma) can also be increased/decreased, until the min/max black/white levels are reached.
(As EOTF/gamma is adjusted between 0-1, there is real no limitation in either direction - brighter/darker - although adjusting it cannot undo clipping, as stated above, and using EOTF/gamma to make a display darker - increasing the EOTF/gamma value - can cause clipping in the blacks.)

As a simple way of thinking about this, the below is a 3D CIE for a 100% P3 display.
Any point within the gamut volume can be moved in aby direction, until it meets one of the boundary edges.
All the points at the edges of the gamut volume can only be moved inwards - subtractively.

Steve

P3 Gamut
P3 Gamut
Steve Shaw
Mob Boss at Light Illusion

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