Histogram not working in VirtualDub?

[Bester]

Ok so, those "slithers" I mentioned in my previous post got me thinking, "this is too good to be true".

I tried to intentionally make them go into the red area but they never do. It is never more than a slither. Just like in this post I found: https://www.digitalfaq.com/forum/vid...am-blacks.html


I essentially have the same issue as @kingbean but with both black and white levels.

What I understood from this post is that, my card cannot capture 0-16 or 235-255 ranges.

But what I could not work out is, is this an issue, and if so, how to remedy?

[timtape]

It may be an issue if your card is presented with a signal brighter than 235, darker than 16, or both.

If brighter than 235, reduce brightness. If darker than 16, increase brightness. If it's both, reduce contrast until both fall within the acceptable range, finally tweaking brightness and contrast to balance both neatly within the window. It's about juggling brightness and contrast.

But also play around with the settings, watching both the picture and the histogram. Deliberately increase brightness so the lighter greys go white. Deliberately reduce brightness so the darker greys go black. See how that agrees with the histogram, which it should.

[Bester]

Even when I deliberately play around with the brightness and contrast I get no more than that small red line as pictured above. I can see the Histogram shifting around, stretching and moving, so it is reacting to the change in levels but it's hiding the full picture from me.

I guess I'll just have to tweak it until there is no red line or stop when the moment the red line first appears.

I'm trying to trust me eye more too but I am beginner at that.

[Acros_13]

Quote:

Even when I deliberately play around with the brightness and contrast I get no more than that small red line as pictured above. I can see the Histogram shifting around, stretching and moving, so it is reacting to the change in levels but it's hiding the full picture from me.

I guess I'll just have to tweak it until there is no red line or stop when the moment the red line first appears.

Hi so I'm not an expert but this is what happens to me as well. It is my understanding that it is because of my frame TBC (in my case a BVTBC8) only passes what it figures to be legal values to the capture card and since the brightness/contrast settings in virtual dub only effect the post TBC and digital domain signal, you can never get it to reflect more than those "slithers" as you call them. The only solution I know of is to trust my eyes to see if it looks like the whites or blacks are being clipped, also often evident in the histogram if the far right or far left is completely vertical implying theres more "data" in the red that the capture card just isn't seeing, and then compressing the luma values using my proc amp settings on the frame tbc itself (in the analog domain, PRE capture card) if that makes sense. Sometimes the blacks or whites are just crushed/clipped no matter what I do, in which case I assume that original recording is just like that to begin with. But if my histogram has somewhat of a gradual slope on the right and left, I usually can assume nothing or at least very little is being clipped. Sometimes this results in a rather flat image, so theres certainly a balance to it, but I suppose the histogram could later be expanded in post whereas if those luma values get clipped that information is lost forever.

if I'm wrong people can correct me. I'm no expert. I tried making a similar thread and also recall not really getting a clear cut solution/explanation. But this is my current understanding. hope it helps.

for the record here was my thread about it: https://www.digitalfaq.com/forum/vid...ping-luma.html

[Bester]

That was actually very helpful. Especially the link!

Sounds like, my Frame TBC is just doing its job but this is a side affect.

I've noticed the slither of red does grow tall or short which I think shows its trajectory.

I need to trust my eyes I think but it's daunting when some of these captures take hours and you don't know where the darkest or lightest scenes are going to be.