"there is more bandwidth for high frequency detail when that detail is riding on a higher brightness background" - indeed! I see it!
The VHS pre-emphasis picture shows 14 dB gain, which is about 500%, not sure where 220% came from.
"Now suppose the image has a full black-to-white fine repeating pattern in some area. In that case, the average background in that area is mid gray by definition, since it is the average of alternating black spots and white spots. This will produce a sideband frequency at the lower limit shown in the diagram. It would be impractical to draw a diagram showing every case of detail amplitude and background gray level, so systems are compared using the kind of diagram you have posted." - this I did not quite get. What is "a sideband frequency at the lower limit", does it have numerically low frequency closer to the left, or does it mean that the difference (I don't want to use deviation here) between this frequency and the carrier will be narrower, so the actual frequency will be closer to the carrier? I am looking at the part to the left of the carrier. And I still haven't reconciled in my mind how the same pattern can be reproduced with different brightness.
Say, I have a pattern, that is, a complex frequency. If I want to make it brighter, I increase the carrier frequency, but then my whole pattern moves to the right, so a frequency that was, say 2 MHz, becomes 2.5 MHz, which means it is a different pattern!
Looks like I am still missing something. I am going to shut up for a while and let you finish
