When you say the "minimum" level displayed, what do you mean as far as the signal goes? Do you mean the lowest voltage value in the signal?
For example say you have waveforms (a) and (b) of a single scan line:
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Would you say that waveform (b) is brighter than waveform (a)?
If so, if the monitor has the signal AC coupled, the DC information about that waveform would be lost, correct? Or did the DC restore actually restore the input DC information? Also, what if the output stage of the video is AC coupled? Then no DC information would get past anyway.
Also, can you give me more information about black level being set relative to the back porch?