Some Notes On Filtering With AviSynth
One of the methods I suggest for improving visual quality on high compression, poorly transferred/encoded source discs, or black and white encodes is to use AviSynth filters. There are multiple ways to do this, including an editor found in the latest versions of DVD Rebuilder, another one built into RB-Opt, AVSEdit (the official AviSynth editor), or any text editor (like Notepad).
While the methods may differ slightly, they all allow you to use the filters described here. If you decide to try adding filters to your video, you should probably come back to this section after you read through the rest of the guide, but I'm putting it first because it applies to more than one program.
So why should you use additional filtering? Well there are a couple of possible reasons. The first, and probably most common, is simply because you're increasing the amount of compression compared to the original DVD. If the compression is within about 20% - 30% of the original, it's unlikely that filters will make much difference, although for many TV series it may still help due to the number of bad transfers and encodes.
For discs that need to be compressed more, it often makes a big difference. Another use for filtering is removing film noise. Some DVDs, like Saving Private Ryan and Band of Brothers, have noise intentionally added for effect. In these cases using additional filters in AviSynth may not help much (depending on your personal taste they may even give you worse results), but there are many movies (especially older, unrestored ones) that have flaws in the film, often age related, which besides requiring bits to encode, can also affect the quality of the original DVD.
AviSynth filters can often remove, or at least hide, many of these flaws. There aren't any perfect solutions, but there are some very good ones, and you can improve both the quality and compression of many movies this way.
Since AviSynth scripts (AVS files) are just text files, all that's required to add lines to one is to edit the text, adding the lines you want. If that sounds easier than you'd expect, trust me - it's really that easy. Now for the hard part. What are you going to add?
Because this guide is for DVD Rebuilder, and not AviSynth, I'm going to stick to simple filters. Fortunately, they're also common filters for many AviSynth gurus to include in their scripts, so you're not missing much by keeping things simple.
Regardless of the filter being used, the basic syntax is filter_name(), replacing filter_name with the actual name of the filter of course. If you want to add multiple filters to run one after another, you can put them on a single line using this syntax: filter_1().filter_2()
Written by: Rich Fiscus