What filter in Vegas would I use for this?

Sticky Fingaz wrote on 10/25/2003, 12:53 PM
I am using Vegas of course and have some video tapes I capped from really high quality sources (a Super VHS master of some music videos to be exact). Dark areas of the videos though, especially if I pause an area that's black, has slight blue and red/purple colors that I am guessing is a result of the VHS tape. It's hard to explain, but just imagine a light blue and red spot here and there that moves around, especially easy to see in paused, black areas (such as a video fading to black).

Of course using the "increase black levels" filter fixes this, but that makes a lot of undesirable effects in the video. Can anyone think of something I can do to remove most if not all of this eyesore (to a videophile like me at least) without compromising the rest of the video? Reducing saturation helps a LITTLE but not a lot.

Thanks in advance!

Comments

GaryKleiner wrote on 10/25/2003, 1:01 PM
Perhaps someone else can come up with a filter that can help you, but you've just described video noise that is part of life with VHS/SVHS. That's why we have DV now.

Gary
Spot|DSE wrote on 10/25/2003, 1:20 PM
Daddylonglegs,
If you have my book on Vegas, there is a section on sharpening and color shifting. While VHS can never be brought back to clean, it can be made to look decent and soften the contrast while keeping color.
Basically, through the use of the convolution filter, at very marginal settings, you can make VHS become more acceptable. Using a tiny bit of Gaussian, such as .001/.002 usually helps with this too.
Sticky Fingaz wrote on 10/25/2003, 1:23 PM
Clever. These videos are older (1991) so considering the circumstances, SVHS is as good as I am going to get. I am in fact using a Super VHS deck going to a DV convertor, but would like to know the best way to get rid of these little color noises. I so far am doing tricks like when the video is a 100% black screen, I toss in a fade to black so it's pure black and not VHS black which has those colors. However if there's an easier way I'd love to know it, especially since it's still somewhat noticeable during the videos with really dark scenes.
Sticky Fingaz wrote on 10/25/2003, 1:57 PM
Thanks, Spot. I may be interested in your book.
Gaussian seems to "blur stretch" my image?? Dunno why it's doing that... However if you could give me a pointer on this convolution filter I'd appreciate it since it's very vague and all I see are numerics listed without anything telling what I am changing.
BillyBoy wrote on 10/25/2003, 4:12 PM
The Convolution filter got to have the best name of all the filters. Who wouldn't want to mess with it?

Its all about pixels and how they get manipulated in a Matrix that can be adjusted resulting in how the surrounding pixels impact on the center pixel within each Matrix. Of couse any given frame of video will be made up of not one but many different Matrixes.

It is rather hard to explain in words exactly what a Convolution Matrix does. When you apply a convolution filter, surrounding pixels of a targeted pixel impact the center pixel. In more traditional filters like unsharpen its the other way around with the center pixel impacting the surrounding ones.

You adjust the Matrix and how it effects the image by building a pattern of negative and/or positive integers. This weighted average is summed and applied to the pixel at the center of each Matrix.

If I understand the math correctly the value of any cell gets multiplied by the coefficient of the convolution kernel at the center of the Matrix.

Note that there are 9 elements to the Matrix. If the center pixel (target) has a positive value and all those surrounding it have a negative values the result should be sharpening. If you reverse it with a negative number at the center and positive numbers surrounding it or if the center value is higher you should get a blur effect. Other special effects are possible and Vegas has several presets.

By altering what sections of the matrix you change you can sometimes get striking results. Sometimes better than other filters that do similar things because you not the filter are setting more parameters. You can also more easily mess things up.

Example you may want to try some even number at center and at either side and all negative numbers everywhere else.

The key is generally you want to keep the matrix symmetrical. In other words you wouldn't want to have a fat positive value at one corner of the Matrix and a high negative one at the other. However if you put say a 5 at the center and a minus 4 at the left most upper corner and also at the right most lower corner that's fine.

PeterWright wrote on 10/26/2003, 1:04 AM
As you're coming from analogue, if you have access to a hardware video mixer, you might be able to tweak the colours before they get digitized.
johnmeyer wrote on 10/26/2003, 2:15 PM
DaddyLongLegs,

The problem you are seeing is a classic artifact of VHS recording technology and can be easily fixed, and without introducing too many artifacts. Unfortunately, you cannot (at present) do it inside of Vegas.

You need to use one of two chroma noise filters:

Giles Mouchard's Chroma Noise Reduction (luma wide 75.00% 15.98% chroma; Chroma 1 100%, 100% chroma; Chroma2 100%, 31.7% chroma; no chroma shift)

or

Video DeNoise 1.2 (default settings)

The second of these two, Video DeNoise was designed specifically for the problem you are describing. Take a look at this page that shows before and after shots and see if the "before" shots exhibit the kind of noise that you're experiencing.

Video Denoise

I used DeNoise until I realized that it was deinterlacing. This created all sorts of artifacts when panning. I couldn't find a way to turn off deinterlacing (there is an earlier version that doesn't de-interlace, but that kept crashing).

I then started experimenting with the first program above (Chroma Noise Reduction) and found I could get even better results than DeNoise, but only if I increased the settings from their default values. Be careful making the settings in the Chroma Noise Reduction plugin too high. At first you won't notice anything bad, but then someone with a red shirt will walk across the scene and you will see smear and other artifacts. The settings I give above are pretty high -- you should go lower, not higher if you are going to change anything.

To run these plugins, you need to get VirtualDub (freeware software program). To create DV AVI files with VirtualDub, you will need some sort of DV encoder. I use MainConcept's DV encoder (not to be confused, as many people in this forum have done, with MainConcept's standalone MPEG encoder, or the Mainconcept MPEG encoder built into Vegas).

One final note, many VirtualDub filters can be used inside of Vegas by installing Satish's excellend PluginPac. Unfortunately, PluginPac can only run filters that work on one frame of video at a time. Most of the noise cleaning plugins, including the two mentioned here, look simultaneously at two or more frames of video.

For more information, search these forums for my user name and the word "VirtualDub" in the search field.