Display Standard - Veritas et Visus

Veritas et Visus Display Standard February 2009
Variations in the transfer function affect not only the picture’s gray scale and contrast, but also the resulting hue
and saturation for all color mixtures, because the individual R,G,B intensities simultaneously dip into different
portions of the transfer function.
The setting of the black level has an increasingly strong affect on the slope of the transfer function at lower signal
intensities. Setting the black level too low reduces the local gamma and increasing it increases the local gamma.
Many HDTVs come set from the factory with a high black level. This also eliminates some dark and shadow detail
in the picture. For digital signals the standard black level is 16, but many HDTVs come set at levels as high as 40.
Figure 3 (on the left): Transfer functions for the Samsung unit with LED local dimming on and off; Figure 4 (on the right):
transfer functions for the Samsung unit for gamma parameter settings
70
Source: DisplayMate Technologies and Insight Media
Figure 3 compares the transfer functions for the Samsung unit with LED local dimming on and off. The transfer
functions are very similar down to about 10% signal. At 5% signal (not shown in this figure) the luminance for the
local dimming on is 0.100 cd/m 2 and for local dimming off is 0.195 cd/m 2 . The differences between the two
transfer functions are due to differences in signal processing between the two modes. The differences are not due to
measurement errors. When local dimming is on, the intensity of the LEDs and the internal video gain, which affects
the panel transmission, both change with the signal intensity and APL change in opposite directions with the signal
intensity and APL in order to deliver the net transfer function.