Black level and Avia (1 Viewer)

[Dave H]

I have a question about setting the black level while using Avia. The screen the you use to set black level has moving bars. Now, I realize that you don't want to be able to see the bar on the left; and you want to barely see the bar on the right. I can see "moving" of the bar on the right very faintly; but if I look at it straight on, I can't see it.
So, my question is, do I set my black level to the point where I can actually SEE the bar or where I can only "sense" it moving because it's so very faint?
I am a perfectionist and was curious.

 

[Guy Kuo]

Here's the scoop. Both bars are slightly brighter than black. The darker one is 1 IRE above black and the brighter one is 2 IRE above black. In an ideal display you'd be able to set things such that both are visible AND the background remains black. We don't have too many ideal displays and people have trouble seeing when the background is just black so I have you set it so the darker of the two moving black bars disappears but the brighter of the two remains visible. That ensures that the background is appropriately black and brackets how far off the mark you can be in both the up and down directions.
The bracketing works this way. If you gradually take brightness down first one bar goes away then the other. The first one disappearing is the point when you adjusted your display such that 1 IRE above black is getting clipped into black. Since the other bar is yet another IRE brighter, its visiblity means that you haven't gone so dark that 2 IRE above black is getting clipped. This two events effectively bracket an adjustment precision of 1 IRE.
In contrast, the usual PLUGE pattern with above and below black bars have the bars about 4 IRE apart from each other in IRE. This yields a larger amount of slop between upper and lower control settings which are marked by visible events. Instead you are relied upon to make the blacker than black bar just become black and immediately stop going darker on the brightness control. You you wait to see above black bar also go away, you're already about 4 IRE too far down.
I wanted to bracket the target point more tightly than older patterns and allow usage with devices which don't pass blacker than black signals yet still give superior precision in indicating the optimum point.
More directly to your query, I'd make it so the brighter one is visible looking straight at it rather than just out of the corner of your eye. The darker one is just about perfect if it is barely detectable by just the sense that something is moving there.
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Guy Kuo
Link Removed
Ovation Software, the Home of AVIA DVD
[Edited last by Guy Kuo on October 26, 2001 at 09:27 PM]

 

[Dave H]

Guy,
I notice on the black bar screen that there is a halo or glare from the (right) white half of screen. If this glare wasn't there, I would probably be able to make the black bars out better...because I can see the bottom of the "brighter" bar, but not the middle of it (again, due to the glare). So, should I take this into account? Should I set it as if the glare wasn't there and ignore the glare?

 

[Guy Kuo]

Do your best to compensate for the glare. This is more of a problem on RPTV's due to their light path and box causing backscatter. If there is a lot of scatter, the brighter of the two bars may be obscured when things are adjusted correctly. In that case, make it such that the brigher bar is just barely visible.
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Guy Kuo
Link Removed
Ovation Software, the Home of AVIA DVD

 

[Dave H]

Thanks for the advice!