Filter for fixing poor VHS contrast intelligently?

[Colmino]

Once again, I showcase my newbie status by being unable to adequately use proper terminology when asking a question. In this case, I anticipate having to deal with a certain problem associated with analog tape recordings, so I'm trying to tackle it well in advance.

Here's a best-case scenario: I have a DVD of an old (commercial) video that is simply an Mpeg2 encoding of the source analog tape. It is quite evident that this is what they did, because the first few seconds of the video start out at pure black, then slowly fade into a dark grey, which turns out to be the analog video's closest approximation of "black".

First, the obvious: Is there a filter which makes this analog tape's "almost black" into a "real black"?

Now it gets a little more complicated. During the course of the video, the actual level of this black changes, depending on how much non-black is being displayed. For example, early on, when the video is essentially all-black with just some opening credits, the black level is at its highest. But later on, when more of the image is devoted to brighter objects, the black level is much closer to a proper "real black". This is not a trick of perception; this is a measurable fact. I don't claim to understand why, but it seems that this is just a curious failing of the analog tape medium.

A filter would definitely have to know what it is doing in order to compensate to the correct degree for each scenario. While I don't doubt it's possible, I have to wonder if there are any black-correction filters which do handle these sorts of varying black levels properly.

Help appreciated!

[sacajaweeda]

Is this a commercial title that's been released on DVD? Maybe that would be a better option than driving yourself crazy with a VHS transfer of crappy source video. Garbage in, garbage out is the rule.

[Colmino]

In the case I outlined above, it is a DVD. While it very definitely has better detail than the original VHS rendition, it's also very clearly from an analog tape source, either because that's all they have to work with, or it's all they were willing to put the effort into working with.

Bottom line is that I don't have the option of tracking down the film negatives and making a perfect no-garbage transfer. I have what I have. I'm just trying to improve it. If the filters don't exist, then bummer.

[johns0]

I dont think any filter is possible to determine which black content to adjust according to scenery,that would require way to much precision.

[Colmino]

That's fine. How about a filter that can go "Okay, so this here is as black as it gets? Right, we'll make that real black, and adjust the rest of the video accordingly." ?

[proxyx99]

Vixen is a very good plugin for color correction for Adobe Premiere. You may also analyse several scenes histogram to adjust black levels and vary the level using keyframe feature. Any good NLE will give you this functionality. Lots of work but it can be done on a scene by scene basis.
Avid 4 and lately Studio 9 has auto correction that may be used for auto adjustment (auto set black level) but will not do it dymamically (self correct).

[wingnut]

Morning,

If you can get the file into virtualdub or virtualdubmod then you can add the "levels" filter. This allows you to sample the whole video and will produce a histogram, you can then slide the level controls for the darkest, lightest and mid ranges until the luminance is corrected. Note that this is working on an "average" so you may still find changes in the black level on certain scenes.

The original problem sounds to me like some sort of AGC, (automatic gain control), problem in the original analogue footage used as a source. It could also be that the original animation didn't always use the same black level though, (look at some 80s cartoons where the contrast jumps up and down all over the place)


Hope that helps


Cheers

Edz

[Rookie64]

You can apply filters for this in Vegas 4.0


Either applying the filters to a certain section/area/frames or crop the section you want and apply to that section only then author the sections as seperate mpeg files.


I've done this several times and it works perfect.