Where/At What Point is the VirtualDub "Levels" Filter Used?

[Avagadro1]

I'm new to video and to VirtualDub.

I have a from-VHS video whose current histogram is greatly squished on both ends. (I am a long-time Photoshop user from which I am very familiar with the tool.)

I observe that VirtualDub has a "Levels" filter (which naturally includes a histogram of the data).

Question: For the VirtualDub Levels/Histogram filter I am describing, is its functionality applied DURING capture or AFTER the video is captured?
Or, by the very nature of being a "FILTER", does that mean that it is to be applied AFTER capture?

Thank you for your help.

[jagabo]

Most VirtualDub filters can be used while capturing (if your computer is fast enough). But VirtualDub's levels filter cannot be used to recover super-blacks and super-brights in YUV video. They are crushed before the filter adjusts levels. Use the Brightness/Contrast filter instead. Even better, use the capture device's video processing amp.

[Avagadro1]

Thank you, jagabo.

I've been experimenting on this matter for a couple of hours. As a long-time Photoshopper, I have been testing multiple iterations of the Levels filter while watching the Histogram overlay. After some tinkering, I was able to make the Histogram appear ideal: just about touching, but not smashed against, both the shadow and highlights ends of the graph. Then a bit of adjustment of the mids ---- and the ONSCREEN result is MUCH better than the video as captured from the VHS tape.

What I imply from your message (see above), however, is that I need not be so exacting with respect to the shadow and highlight end points because, unlike in Photoshop, below Y16 and above Y235, there isn't anything anyway.

Nonetheless, since I'm a long-time Photoshopper and thus I cannot help but think in terms of a nice-looking Levels Histogram, for VHS-captured video, is it ok to go through the process of creating a "proper" looking Histogram in the Levels filter.

Thank you.

[davexnet]

The filter can sample frames from the whole video and give histogram based on the average levels.
Use that as a guide to set the levels, if any

[Avagadro1]

Thanks for your help.