Originally Posted by Charles R
Here is a post from Guy Kuo. I may be misunderstanding the issue (certainly possible). I thought with 7.5 IRE blacker than black could be displayed and not at 0 IRE...
Guy's remarks and mine are consistent.
First, Guy's comments and mine are referring to two different processes and signals originating from two different sources. In the case where I was responding to your question, I am considering an analog signal originating from an NTSC source. And, I am talking about converting this analog signal to digital at either video or pc levels. Black for the NTSC source is 7.5 IRE. There is no blacker-than-black in this case and the lowest value (black) after conversion is either 16 or 0, depending on the encoding level used. Basically, it is the encodng process and selection of black as 0 or 16 that determines whether something is "video" or "pc" level.
Guy's comments are specific to a DVD player (or similar source) that converts a digitally encoded signal (on the dvd or other media) back into an analog signal before sending it to the display as an analog signal (voltage). In converting to analog, the player's design determines the final output voltage. Since the dvd is encoded at video levels, black = digital 16. (Key point: there are no voltages recorded on the source media.) Depending on who did the encoding and how it was encoded, the dvd may or may not contain values less than 16 (blacker-than-black). It is in the case of encoded digital values of less than 16 that the player could, if designed to do so, read a digital value that is less that 16 and output a blacker-than-black signal of less than 7.5 IRE (if the pedestal is set). However, at this point, the output signal is neither at video or pc level. It is an analog signal whose primary characteristic (in regard to black) is its voltage. A 7.5 IRE signal can originate from a dvd whether it was video or pc encoded. Granted, a less than 7.5 IRE signal could not originate from a pc encoded media. Nevertheless, the encoding (pc or video) does not determine the level of the output voltage and thus the encoding method should not be used to describe whether blacker-than-black or 7.5 IRE is present at the display.
Not sure I'm doing such a great job of "clarifying."