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