In fact it’s worse than that – it’s linear for the first 10% of the range. However, if you don’t want to bother with a precise BT.1886 calculation a ‘best approximation’ of this would be a gamma of 2.2 in the low end of the curve rising to a gamma of 2.4 at the high end. The new BT.1886 specification (from 2011) is complex and its precise recommendations vary depending upon the white level, and especially the black level, of the display.
However, a straight power curve of 2.4 is correct only if the display has a zero black level and an infinite contrast ratio, which no real-world display has.
Lcd gamma control reference tv#
Like sRGB (the Adobe colour space for graphics working) and Rec.601 the “scene-referred” gamma of 2.2 is specified (in 1992 TV cameras were still tube’d devices) but the display gamma is governed by a complicated transfer law which many people have taken to be closer to a gamma of 2.4. They also made a subtle change to the definition of gamma. When Rec.709 came along in the early nineties (for HD television) they changed a few things new colour primaries, new luminance transfer function, wider gamut etc. If you get this wrong you wind up with blacks and whites matching but all the shades in between don’t – pictures either appear washed-out or all the detail is crushed out of the dark areas of the picture depending on which way you get it wrong. it looks the same on the monitor as well as to the naked eye) you have to invert the gamma response of the camera at the display end. This is required because television cameras don’t have a linear transfer characteristic and to make a black-white ramp match (i.e. For all the decades of standard definition work a gamma of 2.2 has been used. I’ve been calibrating TV displays for around twenty-five years and have always leaned on the BBC practice of setting peak white at 80Cd/m2 and the white point at 6504k.
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