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Frame Movement in the RetroScan Universal


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#1 Guy Burns

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Posted 27 May 2016 - 03:49 AM

I have recently had films scanned on the RetroScan Universal as part of a wider comparison of 8mm film scanners. I asked for the perforations to be included so that I could check the quality of registration and determine the causes of frame movement. Here’s what I found for Standard 8mm and Super 8mm. Video files mentioned below can be downloaded from: http://www.mediafire...(RetroScan).zip

 

The easiest way to see the frame movements is to open the files in Quicktime and step through, frame-by-frame.

 

Frame Jumps caused by camera

One of the films (R01a, Standard 8, 1947) has a cyclic, horizontal movement of the frame. Every six frames the image moves sideways relative to the perforation, then gradually moves back over the next five frames. There is only a minor impact on frame registration.

 

Frame Jumps caused by scanner

At Splices

At splices, the RetroScan typically causes a vertical jump of between 5% and 15% of frame height, mostly at the lower end of that range. The jump seems to be caused by the splice tape covering part of the perforation, thus confusing the perforation detector. Examples are R01b, R01c, R02a, R02b, R04a, R04h.

 

For Standard 8, the jumps occur 7 frames before the splice; for Super 8mm, 10 frames before the splice. The jumps last until the splice itself is scanned, then the frame reverts to the normal position.

 

I suppose this means that, for the RetroScan, there is a single perforation sensor at a fixed distance behind the capture point.

 

At Scene Changes

A small number of jumps are caused by scene changes, where the incoming scene is brighter than the previous scene. The perforation detector seems to be confusing part of the bright scene with the perforation. The jump is typically 5% to 10% of frame height and lasts 1-10 frames.

 

Examples are: R04b, R04c, R04e, R04j

 

At Zooms

A zoom, in or out, can cause a jump, probably because of a brightness change associated with the zoom. i.e. if the zoom causes a white area to become larger (R04g), the extra brightness upsets the perforation detection. But a zoom into a dark area (R04L) can also upset the perforation detection. Typical jumps were 5% and lasted 10 frames.

 

Examples: R04d, R04i, R04j, R04k, R04L

 

Bright areas

If a bright area is near the perforations, it can cause erratic frame jumps. Examples are R04g, R04k

 

Unexplained Jumps

Occasionally there are erratic jumps that I can’t explain (R04f).

 

Dirt in Perforation

Dirt partly blocking the perforation can cause a jump (R04m).

 

 

Summary

1. All frame jumps were vertical, not horizontal.

2. Jumps can be caused in several ways: zooms into bright or dark areas, scene changes into a bright scene, dirt in a perforation, or bright or dark areas around the perforations.

3. For scans which are cropped inside the image area, frame jumps will cause problems because they will cause loss of part of the image.

4. Frame jumps will be less of a problem if the scan area is expanded by 10-15% of frame height because no part of the image will be lost during the jump. The jumped frames may be out of registration with the others, but at least they are intact.

 

 

Ques 1

Do high-end machines – Scan Stations, Kinettas, Xenas and the like – have any of the above problems?

 

Ques 2

Given that most home movies tend to have camera wobble and would benefit from a small amount of stabilization in a video editor – stabilization that would also bring the jumped frames into alignment – how important, really, is accurate frame registration for home movies?

 

 


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#2 Perry Paolantonio

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Posted 27 May 2016 - 08:01 AM

I can only speak for the ScanStation here, so everything below is about that machine:

 

The perforation detection is done by overscanning the film from edge to edge. The perforation itself is detected using machine vision algorithms, and is placed in a fixed location on the X and Y axis in the scanned frame. The Scanner gate is designed such that the film can "float" through the gate and the film itself is not positioned mechanically other than by using some rollers on either side of the gate to make sure that it stays on track. That is, no spring-loaded edge guides or anything like that. All registration is done optically. 

 

For Super 8, which is a special case because Super 8's perforations are not precisely placed relative to the edge of the film, the scanner does things a bit differently: vertical registration is done with the perf, horizontal is done using the edge of the film. 

 

In terms of splices, it really all depends on the splice itself. a clean tape splice will generally run through just fine, but of course you can still see it sometimes, because it's a physical layer of stuff on the film. The v-groove channel that the film passes through on the ScanStation minimizes focus changes in these situations, because only the very edges of the film are actually touching anything in the gate. 

 

Cement splices can vary, but because they are by nature an overlapping of the film, the film is thicker at the point of the splice and that can cause the film to rise up at one end of the frame, which can cause a momentary focus issue until the frame passes. 

 

Splice bumps shouldn't happen, unless it's a sloppy splice that's not well aligned. Most consumer splicers didn't make very precise splices. Some cut right through the middle of the frame, some along the frame line. Some used press tapes that covered several frames of film, others used tape that goes across the splice and only covers 2 frames. It's a consumer format, and expecting it to be perfect, especially at splices, is unrealistic, regardless of the scanner used. 

 

I don't know how the Retro8 does its registration, but it sounds like it's got some issues if it's having trouble at points where the exposure changes. That shouldn't have an effect on the registration.

 

-perry


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#3 Guy Burns

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Posted 27 May 2016 - 10:40 PM

It's a consumer format, and expecting it to be perfect, especially at splices, is unrealistic, regardless of the scanner used.

 

Thanks for the comments, Perry. I have very few expectations at this stage. I'm testing scanners to find out their limitations and then to work within that. It looks to me like overscanning at 15% of frame height is essential on the RetroScan – if you want to be sure of seeing all the image.

 

I'm assuming the ScanStation has small frame jumps from various causes. Any idea of the amount of overscan needed so as to be reasonably sure not to lose part of the image? 2%, 5%?

 

I sent an email last week re scanning my films. Did you receive it?


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#4 Anthony Schilling

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Posted 29 May 2016 - 12:12 PM

I've been using the Retro Universal since it came out. Side to side instability is usually cause by warpage in the take up reel, i always make sure to give them a stretch before hand. Frame jumping can be caused by light flooding the sprocket holes and/or the sensor knob not adjusted properly. I've scanned clear edge film without any jumping just by turning the sensor way down. Vertical stability is camera dependent... Super 8 and even my Bolex H16 will have some slight frame line movement at times, but S16 shot on an SR3 is rock solid on my machine...No frame line movement what so ever. The Universal takes a little getting used to as there are so many things to adjust to your needs. My guess is that 


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