Restoration tips: Overlap matching

[spoRv]

OVERLAP MATCHING

What is the Overlap matching?

When two images of different sizes are used to improve the final result.

Could you be more specific?

Usually this is used when two different versions of the same movie are available at different aspect ratios.

Let’s say you want to restore a movie that is not available in high definition, and you want to upscale a DVD or a laserdisc capture. If you are lucky, an anamorphic DVD is available, so a theoretical 720×576 (PAL) or 720×480 (NTSC) max resolution could be achievable. But, if the original aspect ratio of the movie is 2.35:1, then you have only 720×432 (PAL) or 720×360 (NTSC). Well, enough resolution left to do a decent upscale. However, if the DVD is not anamorphically enhanced, actual resolution drops to 720×324 (PAL) or 720×252 (NTSC).

But what if the only (or the best) available low definition sources are analog? In this case, a 2.35:1 original resolution in laserdisc could be at maximum 576×324 (PAL) or 576×262 (NTSC), while VHS could be 328×324 (PAL) or 328×262 (NTSC)… pretty poor…

So, how it’s possible to improve the quality of such low resolution sources? It’s easy! Overlap a pan&scan version of the same movie over the letterbox version! The P&S version of a laserdisc could be 576×576 (PAL) or 576×480 (NTSC), while VHS could be 328×576 (PAL) or 328×480 (NTSC). Can you see the differences?

EXAMPLE:

here you can see how a P&S version overlapped to a letterbox version, upscaled, have a better resolution than the latter; this will lead to better details in the center of the image, leaving less detailed image at the borders. It is also possible to use two letterboxed versions (like 1.66:1 and 2.35:1) – even if difference in details will be less than using a P&S version, it nevertheless improve definition a lot.
A lower difference in aspect ratios between sources makes the final resolution only slightly better, but often this avoids all the image cropping and variations that lie in the pan&scan version.

Can I use an open matte version instead of pan& scan?

It is often futile to use an open matte version with a letterboxed version both from the same format, as active image have the same effective vertical resolution; however, it is possible to use an open matte version of an higher resolution source overlapped to a lower resolution source.
So, for example, an open matte DVD (with higher horizontal resolution) overlapped to a letterbox laserdisc; or an open matte laserdisc or DVD (both with higher horizontal resolution) overlapped to a letterboxed VHS, will increase the details clarity of the final upscaled version.

What about high definition formats, like Blu-ray and HDTV sources?

in some rare cases, the open matte version of the same (or comparable) format of the letterbox version has a better resolution – due to several factors like different masters, encoding, bitrates etc. – in such cases, it’s possible to use the Overlap matching method, although usually with lower quality improvement in comparison to previous cases.

NOTE: consider that pan&scan cropping vary usually everytime between shots, and often during a single shot; so this method is really really hard to follow, much more than the “Slice technique”…

Top, upscaled DVD, bottom, upscaled DVD with HDTV overlapped:
[Image: matrix_083217.jpg]
http://s27.postimg.cc/fwskn8q8x/matrix_083217.jpg

same image as the previous second one, not cropped:
[Image: matrix_PLUS.jpg]
http://s22.postimg.cc/3ucfmeuj3/matrix_PLUS.jpg

WARNING: this is a very difficult technique, and could be really hard and time consuming to find out the perfect settings; I did this simple match in an hour, and both previous and next shots have completely different setting… be aware!
Comments, improvements, corrections are welcome!

[spoRv]

Must add that it's possible to use the overlap matching techniques with two sources (different version of the same video) to improve the quality; an example is two HDTV captures, one MPEG-2 and one AVC; while usually the latter is better, sometimes we have a very high quality MPEG-2 - high bitrate, but older tech - while the AVC has lower quality and bitrate, but retains some more details...

Overlay them would improve (often, but not always) details, or phase out noise, or smooth blocking, or several of the previous combinations - your mileage may vary; what I noted is that every time the noise is well deleted, better than a denoise filter, retaining more image details. Blocking, too, are usally considerably smoothed, while detail improvements depends on case-by-case situation.

I should add also that sometimes there are two caps, one 720p and one 1080i, where the former has an higher bitrate than the latter, hence it's a good idea to consider to merge them using this technique - just pay attention to use a very good upscale method to let the 720p to 1080p, and also a good deinterlacer and IVTC filter.

Overall results of this technique may vary from poor (not often) to good (usual case) to great (difficult, but possible); if you are lucky to get three different versions that align perfectly, go on!

[Stamper]

Awesome. I was wondering if Mad Max 3 could be improved by applying the DVD to the High Def version, as the HD have blown out highlights in many shots.

[spoRv]

If the DVD, once upscaled properly, would match, I think so... but I must add that sometimes it doesn't happen, due to different masters used - sometimes they are angled differently, and even one degree could ruin everything!

[spoRv]

ADDENDUM:

the technique could be used to add top and bottom slices to a non-full screen image, to get an open matte version



this could be useful if the center image is from an high quality source (like BD) and the top and bottom, which are clearly the open matte version, are from lower quality/definition source (HDTV 1080i/720p/DVD).

Some test examples:

Aliens - http://screenshotcomparison.com/comparison/212658
Waterworld - https://diff.pics/kgTWwcqKEsvI/1

[Evit]

[Chewtobacca]

The principle's straightforward enough. It's resizing so that you can overlay one clip onto another that's the difficult part. It's very fiddly and drives me nuts. I don't know how Andrea can stand processing a whole film like this.

[spoRv]

Haven't processed a whole film (yet)... *if* a film have a one-for-all setting, it's a breeze!

I think it's possible to do such with the following (still to test, though!):

Aliens
Jurassic Park
Waterworld

...we'll see!

[nightstalkerpoet]

What is your preferred resizing method for this? I know some of them shift the image too much.

[spoRv]

What is your preferred resizing method for this? I know some of them shift the image too much.

Please elaborate further... method as type of resizer, like spline, lanczos etc.? Or else?