24p HD Restoration

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There’s a lot of good film content that only lives on 4×3 SD 29.97 interlaced videotape masters. Certainly in many cases you can go back and retransfer the film to give it new life, but for many small filmmakers, the associated costs put that out of reach. In general, I’m referring to projects with $0 budgets. Is there a way to get an acceptable HD product from an old Digibeta master without breaking the bank? A recent project of mine would say, yes.

How we got here

I had a rather storied history with this film. It was originally shot on 35mm negative, framed for 1.85:1, with the intent to end up with a cut negative and release prints for theatrical distribution. It was being posted around 2001 at a facility where I worked and I was involved with some of the post production, although not the original edit. At the time, synced dailies were transferred to Beta-SP with burn-in data on the top and bottom of the frame for offline editing purposes. As was common practice back then, the 24fps film negative was transferred to the interlaced video standard of 29.97fps with added 2:3 pulldown – a process that duplicates additional fields from the film frames, such that 24 film frames evenly add up to 60 video fields in the NTSC world. This is loaded into an Avid, where – depending on the system – the redundant fields are removed, or the list that goes to the negative cutter compensates for the adjustments back to a frame-accurate 24fps film cut.

df_24psdhd_5For the purpose of festival screenings, the project file was loaded into our Avid Symphony and I conformed the film at uncompressed SD resolution from the Beta-SP dailies and handled color correction. I applied a mask to hide the burn-in and ended up with a letter-boxed sequence, which was then output to Digibeta for previews and sales pitches to potential distributors. The negative went off to the negative cutter, but for a variety of reasons, that cut was never fully completed. In the two years before a distribution deal was secured, additional minor video changes were made throughout the film to end up with a revised cut, which no longer matched the negative cut.

Ultimately the distribution deal that was struck was only for international video release and nothing theatrical, which meant that rather than finishing/revising the negative cut, the most cost-effective process was to deliver a clean video master. Except, that all video source material had burn-in and the distributor required a full-height 4×3 master. Therefore, letter-boxing was out. To meet the delivery requirements, the filmmaker would have to go back to the original negative and retransfer it in a 4×3 SD format and master that to Digital Betacam. Since the negative was only partially cut and additional shots were added or changed, I went through a process of supervising the color-corrected transfer of all required 35mm film footage. Then I rebuilt the new edit timeline largely by eye-matching the new, clean footage to the old sequence. Once done and synced with the mix, a Digibeta master was created and off it went for distribution.

What goes around comes around

After a few years in distribution, the filmmaker retrieved his master and rights to the film, with the hope of breathing a little life into it through self-distribution – DVDs, Blu-rays, Internet, etc. With the masters back in-hand, it was now a question of how best to create a new product. One thought was simply to letter-box the film (to be in the director’s desired aspect) and call it a day. Of course, that still wouldn’t be in HD, which is where I stepped back in to create a restored master that would work for HD distribution.

Obviously, if there was any budget to retransfer the film negative to HD and repeat the same conforming operation that I’d done a few years ago – except now in HD – that would have been preferable. Naturally, if you have some budget, that path will give you better results, so shop around. Unfortunately, while desktop tools for editors and color correction have become dirt-cheap in the intervening years, film-to-tape transfer and film scanning services have not – and these retain a high price tag. So if I was to create a new HD master, it had to be from the existing 4×3 NTSC interlaced Digibeta master as the starting point.

In my experience, I know that if you are going to blow-up SD to HD frame sizes, it’s best to start with a progressive and not interlaced source. That’s even more true when working with software, rather than hardware up-convertors, like Teranex. Step one was to reconstruct a correct 23.98p SD master from the 29.97i source. To do this, I captured the Digibeta master as a ProResHQ file.

Avid Media Composer to the rescue

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When you talk about software tools that are commonly available to most producers, then there are a number of applications that can correctly apply a “reverse telecine” process. There are, of course, hardware solutions from Snell and Teranex (Blackmagic Design) that do an excellent job, but I’m focusing on a DIY solution in this post. That involves deconstructing the 2:3 pulldown (also called “3:2 pulldown”) cadence of whole and split-field frames back into only whole frames, without any interlaced tearing (split-field frames). After Effects and Cinema Tools offer this feature, but they really only work well when the entire source clip is of a consistent and unbroken cadence. This film had been completed in NTSC 29.97 TV-land, so frequently at cuts, the cadence would change. In addition, there had been some digital noise reduction applied to the final master after the Avid output to tape, which further altered the cadence at some cuts. Therefore, to reconstruct the proper cadence, changes had to be made at every few cuts and, in some scenes, at every shot change. This meant slicing the master file at every required point and applying a different setting to each clip. The only software that I know of to effectively do this with is Avid Media Composer.

Start in Media Composer by creating a 29.97 NTSC 4×3 project for the original source. Import the film file there. Next, create a second 23.98 NTSC 4×3 project. Open the bin from the 29.97 project into the 23.98 project and edit the 29.97 film clip to a new 23.98 sequence. Media Composer will apply a default motion adapter to the clip (which is the entire film) in order to reconcile the 29.97 interlaced frame rate into a 23.98 progressive timeline.

Now comes the hard part. Open the Motion Effect Editor window and “promote” the effect to gain access to the advanced controls. Set the Type to “Both Fields”, Source to “Film with 2:3 Pulldown” and Output to “Progressive”. Although you can hit “Detect” and let Media Composer try to decide the right cadence, it will likely guess incorrectly on a complex file like this. Instead, under the 2:3 Pulldown tab, toggle through the cadence options until you only see whole frames when you step through the shot frame-by-frame. Move forward to the next shot(s) until you see the cadence change and you see split-field frames again. Split the video track (place an “add edit”) at that cut and step through the cadence choices again to find the right combination. Rinse and repeat for the whole film.

Due to the nature of the process, you might have a cut that itself occurs within a split-field frame. That’s usually because this was a cut in the negative and was transferred as a split-field video frame. In that situation, you will have to remove the entire frame across both audio and video. These tiny 1-frame adjustments throughout the film will slightly shorten the duration, but usually it’s not a big deal. However, the audio edit may or may not be noticeable. If it can’t simply be fixed by a short 2-frame dissolve, then usually it’s possible to shift the audio edit a little into a pause between words, where it will sound fine.

Once the entire film is done, export a new self-contained master file. Depending on codecs and options, this might require a mixdown within Avid, especially if AMA linking was used. That was the case for this project, because I started out in ProResHQ. After export, you’ll have a clean, reconstructed 23.98p 4×3 NTSC-sized (720×486) master file. Now for the blow-up to HD.

DaVinci Resolve

df_24psdhd_1_smThere are many applications and filters that can blow-up SD to HD footage, but often the results end up soft. I’ve found DaVinci Resolve to offer some of the cleanest resizing, along with very fast rendering for the final output. Resolve offers three scaling algorithms, with “Sharper” providing the crispest blow-up. The second issue is that since I wanted to restore the wider aspect, which is inherent in going from 4×3 to 16×9, this meant blowing up more than normal – enough to fit the image width and crop the top and bottom of the frame. Since Resolve has the editing tools to split clips at cuts, you have the option to change the vertical position of a frame using the tilt control. Plus, you can do this creatively on a shot-by-shot basis if you want to. This way you can optimize the shot to best fit into the 16×9 frame, rather than arbitrarily lopping off a preset amount from the top and bottom.

df_24psdhd_3_smYou actually have two options. The first is to blow up the film to a large 4×3 frame out of Resolve and then do the slicing and vertical reframing in yet another application, like FCP 7. That’s what I did originally with this project, because back then, the available version of Resolve did not offer what I felt were solid editing tools. Today, I would use the second option, which would be to do all of the reframing strictly within Resolve 11.

As always, there are some uncontrollable issues in this process. The original transfer of the film to Digibeta was done on a Rank Cintel Mark III, which is a telecine unit that used a CRT (literally an oscilloscope tube) as a light source. The images from these tubes get softer as they age and, therefore, they require periodic scheduled replacement. During the course of the transfer of the film, the lab replaced the tube, which resulted in a noticeable difference in crispness between shots done before and after the replacement. In the SD world, this didn’t appear to be a huge deal. Once I started blowing up that footage, however, it really made a difference. The crisper footage (after the tube replacement) held up to more of a blow-up than the earlier footage. In the end, I opted to only take the film to 720p (1280×720) rather than a full 1080p (1920×1080), just because I didn’t feel that the majority of the film held up well enough at 1080. Not just for the softness, but also in the level of film grain. Not ideal, but the best that can be expected under the circumstances. At 720p, it’s still quite good on Blu-ray, standard DVD or for HD over the web.

df_24psdhd_4_smTo finish the process, I dust-busted the film to fix places with obvious negative dirt (white specs in the frame) caused by the initial handling of the film negative. I used FCP X and CoreMelt’s SliceX to hide and cover negative dirt, but other options to do this include built in functions within Avid Media Composer. While 35mm film still holds a certain intangible visual charm – even in such a “manipulated” state – the process certainly makes you appreciate modern digital cameras like the ARRI ALEXA!

As an aside, I’ve done two other complete films this way, but in those cases, I was fortunate to work from 1080i masters, so no blow-up was required. One was a film transferred in its entirety from a low-contrast print, broken into reels. The second was assembled digitally and output to intermediate HDCAM-SR 23.98 masters for each reel. These were then assembled to a 1080i composite master. Aside from being in HD to start with, cadence changes only occurred at the edits between reels. This meant that it only required 5 or 6 cadence corrections to fix the entire film.

©2014 Oliver Peters

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