This setting is only available (not "grayed-out") when the input signal, from a device connected to the TV via HDMI, is set to RGB.
This setting compensates for effects caused by a low black level, such as low contrasts and dull colors. If the external device you have connected does not support the "Full-Range" signal that the TV can support, you can enable the "HDMI Black Level" function and have the TV compensate.
All video discs, including Blu-rays, DVDs and Video CDs, are encoded as YCbCr which has a native "limited" color range of 16-235 (for 8-bit sources). Most HDMI devices (Blu-ray players, Satellite receivers, Cable boxes) will output a YCrCb signal. It is best to set these source components to output YCbCr not
An HDMI device that can output an RGB signal (Computer, Gaming console) can usually be set to output either a "limited" (Video level) color range of 16-235 or
a "full" (PC level) color range of 0-255.
A "Full-Range" 8-bit
RGB signal of 0-255 refers to the number of color variations (256) that are available in each of the Red, Green, and Blue channels (for a total of 16.78 million possible colors/shades).
For a "Limited-Range" 8-bit
signal (16-235), a total 10.65 million colors/shades will be available. Note: The human eye can discriminate up to ten million distinct colors (color variations).
RGB signal (i.e. Deep Color) has a "Full-Range" color depth of 0-1023 (1,024 color variations available in each of the Red, Green, and Blue channels for a total of 1.07 billion
In a Y’CbCr encoding system, the luminance information (or luma
signal) is transmitted separately from the color information and a "color difference system"
is used to derive green. Y′ (pronounced Y-prime) is the luma
component and Cb & Cr are the blue-difference and red-difference chroma
components - they are derived from B-Y’ and R-Y’. In practical application, YCbCr is no different than RGB in terms of quality.
[For more on the Y’CbCr encoding system and Chroma Subsampling, see THIS POST
When playing back a "Limited-Range" (16-235) RGB signal (Video level), you should set "HDMI Black Level" setting to "Low" in order to match
the input signal and get all the encoded information as it was intended. If you mismatch and play it back with the "Full-Range" RGB setting ("Normal"), you'll clip off the black and white levels and black will look "dark gray" (elevated blacks) and the image will appear "washed-out".
When playing back a "Full-Range" (0-255) RGB signal (PC level), you should set it to "Normal".
The "Low" setting sets the "HDMI Black Level" enhancement for a "Limited-Range" RGB input of 16-235. The "Normal" setting sets the "HDMI Black Level" enhancement for a "Full-Range" RGB input of 0-255. Note: If you are not sure which setting to choose, just leave it on "Auto".
When a YCrCb signal is detected, the "HDMI Black Level" setting will be unavailable ("grayed-out").