C100: Interlacing 30PsF Issues

W

wojdarm

Active member
Could use some advice and thoughts on this. We want to shoot and edit in 30P but with the C100 we can only shoot 30PsF. Our normal workflow is to rewrap the footage from .MTS to Prores422 using Clip Wrapper, then do a technical grade in Resolve output a Prores422 out of Resolve for client use or editing. We are have extreme problems with apparent interlacing that occurs after Clip Wrapper and is only marginally better when using Aunsoft. It really looks like the frames are not combined and we are seeing just one field. How do we get from a 30Psf to a 30P prores422 file that is a true progressive file? I know this comes up a lot but I've not seen a real resolution besides bringing it into Premier or After Effects first.

Here's what we are seeing:

After Uploading the image the alaising goes away. Look at this download to really see it:
https://dl.dropbox.com/u/9970851/Water Street/Screen Shot 2013-02-20 at 12.18.53 PM.png?dl=1

Screen Shot 2013-02-20 at 12.18.53 PM.jpg

Could this also be an issue because of the way the camera treats the Red's?

Bob
 
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It does look like an extreme 4:2:0 thing - as one gets under theatrical lighting sometimes. But there is that odd 'hooking' above each block.

I've seen this before in my own footage when the codec was under pressure with motion, but haven't yet had time to go out and re-create this.

I don't have a solution, I have a half-baked theory - that maybe the Canon PSF means the luma's progressive but the chroma's still interlaced. Complete and utter nonsense I'm sure, but we have to start somewhere.

Also, can you run that clip through 5DtoRGB using its chroma resampling method?
 
Matt,

5DtoRGB is a good idea but I can't seem to open C100 footage or Clip Wrapped proves footage into it. Is there a trick to it somewhere?

Bob
 
I'm curious if you have access to PP (CS6). I can import 30PsF footage into PP directly and don't see any interlacing artifacts (Modify -> Conform to progressive scan). If you can try this out and still see the artifacts, it may tell you that it's a chroma issue and not a PsF issue. If you don't have PP and would like to send me a short clip to try, let me know.
 
Steve,

We see the same thing in both Premier and even Smoke. Matt's comment about 4:2:0 could be right on. I saw this in a couple of other shots that had high chroma in the reds. This is something to check as the camera may have a real issue here. If it's a result of the codec this camera may have severe problems.

Bob
 
If Steve says he can import into premiere and it looks fine, something must be off about your shots. I know the AF100 chroma clipped a bit in the reds, but it looks like you have more problems going on here than just chroma. I would highly doubt canon made a major mistake with how this camera handles shooting in other frame rates, but rather a workflow error. Just a guess though.
 
Hmmm, 30psf stuff works fine for me in Premiere Pro 5.5 too using the "Modify -> Conform to progressive scan" workflow. Can't seem to access your video file (get a 404 error) to check out the clip though.
 
MattDavis said:
I don't have a solution, I have a half-baked theory - that maybe the Canon PSF means the luma's progressive but the chroma's still interlaced. Complete and utter nonsense I'm sure, but we have to start somewhere.
Click to expand...

The sensor works as expected and reads and stores each of the color channels (R,G1,G2,B) as 'whole' frames.

I can't download the original footage, but I'm sure you are right about it being 4:2:0.

There are situations that will pronounce the lack of color information in the internal recording, especially since the footage normally is so sharp. Jagged edges that would otherwise be smoothed out appear jagged on the C100.
 
You can see them on other parts of the frame as well and just in the reds, so how does that make it a 4.2.0 thing?
 
Appreciate the comments so far. If it's a problem in chroma sub sampling it seems to me it very well could show it self in situations like this where the chroma is peaking and the codec can't handle it properly. I'd also guess that we'd see more in a certain primary than other colors which is what we have here. That stepping looks like an interlaced frame so that's where we started. I think my next step is to retest in the studio with some saturated shots to see if I can recreate this problem. Our workflow could have an issue somewhere but I really don't think so. I saw this same thing in another shot where a small red flag was waving and had a deinterlaced look to it. All cameras and codecs have their issues and finding them and knowing how to work around them is part of the game.

Bob
 
wojdarm said:
Could this also be an issue because of the way the camera treats the Red's?
Click to expand...
This has nothing to do with the camera or the codec.

There are two distinct chroma upsampling methods. One is used for progressive images, the other for interlaced images. What you're seeing is the result of the wrong method being used, usually due to the file being flagged as interlaced when it's not.

5DtoRGB allows control over which method is used by selecting the appropriate one in the "Chroma Mode" dropdown. This choice overrides any flags in the file. 5DtoRGB shouldn't have any trouble transcoding this file properly.

You can download 5DtoRGB Lite for free here:

https://itunes.apple.com/us/app/5dtorgb-lite/id502347425?mt=12
 
Thomas,

Thanks, 5dtoRGB seems like the right tool. I was trying to open the c100 files but was unable to directly. Ran out of time to work on it more today but is there some trick to open the files that are in the "private" folder that the c100 creates? Any help you can give would be appreciated.

Bob
 
Wojdarm,
I experienced this problem as well as you when shooting at 25psf. The last version of 5DtoRGB should fix it. Try feeding it with the mts directly and it should see the file but no timecode.
The problem I'm having now is that I can't get the sound when transcoding with 5DtoRGB (full version). The Lite version works fine instead, but it's a pain to convert a bunch of files one by one.
 
That's a pretty good write up. I think the " not suitable for green screen work" is a little misleading. I shot some green green stuff the other day with the internal codec and it keyed great. I would say better than my af100 which is the same codec. You will yield slightly better results with an external recorder, but to say you can't do it with the internal codec is a little over the top.
 
swanny said:
to say you can't do it with the internal codec is a little over the top.
Click to expand...

There are green screens and there are green screens. I have shot against my portable green screen in several locations now using minimal (and I mean very minimal) lighting...mostly available light for the green screen. These were talking heads for corporate work. It keyed fine in CS6 on my Win7 laptop...AVCHD internal codec.
 
Great to hear that you are doing well, keying from the internal codec. I'll add that info to what I've written.

And that further supports my own feelings that the internal is good for almost anything. But I'm sure that a user wanting to err on the side of caution would opt for an external recorder for green screen. The shot is bound be locked down anyway, so I wouldn't think that a small Ninja 2 or similar would be in the way.

Anyway, good to hear.
 
Just wanted to add a little support for our dear 4:2:0 codec - AVCHD. I did a little shoot a while back, green screen in an office. I brought my Pix220 recorder for a 4:2:2 recording.

A little back-story - have had a lot of success doing this kind of shoot with EX1Rs using XDCAM-EX - also 4:2:0 at 35 Mbits per second. FS100 (and to a lesser extent the FS700) failed at doing this kind of shoot on both their native codec and using an external recorder as there just wasn't the detail in the image compared to the 3-chip EX1. However, for general use, 24 Mbit AVCHD compared very favourably with XDCAM-EX at 35 Mbit simply because AVCHD uses H.264 which has a more efficient codec - does more with less.

Back to Chromakey. C100, with pix attached, filmed internal and external, fully intending to use Pix version. Tried AVCHD and found it very much like the XDCAM-EX material with the EX1 - plenty of detail in the image without dialling in any 'sharpness', although I found out later that WDR did have some sharpening in it.

As with the EX1 footage, it shows that there are 'chromakeyers' and there are 'Chroma Keyers', and there are hybrids. Hybrid keyers find the basic background via the colour (or range of colours) which will look awful if keyed from - like it's cut out from a cheese grater. However, hybrid keyers then find out where edges are, and do various computations with the luminance signal (mono only) to create a reasonable edge matte. Add the edge and the general key, and hey presto: you get a fairly passable chromakey so long as your spill wasn't awful and you didn't dial in sharpness.

Best results came from AE and KeyLight after a bit of fiddling (what a surprise), but managed to get acceptable (that's ACCEPTABLE, not cinema quality) results from the FCPX internal keyer, mainly by dialling out all its 'help'. Both beat the previous 'champ' at this - DVmatte Pro from Digital Garage. I now understand why Alex Lindsay stopped work on it when this keyer appeared in Motion and now FCPX. But if you're doing it for money or accolades, Keylight still rocks.

So - will I shoot chromakey on the internal codec? No, I'll still use an external recorder. Will anyone notice? You lot will. I do. My clients? My audience out there on the web? Probably not. I'd like to say the externally recorded material was easier to key, but if I put hand on heart, no - it wasn't that much easier. What makes for an easier key? Software, lighitng, resolution.

Taking this up one level, to get motion tracking markers, transparency, reflections, this is where you need to abandon 8 bit and 4:2:0 and go as deep and as high resolution as you can. Would love to play with BMCC as a chromakey camera, and I guess Red/Alexa are perfectly happy here too. But I don't do that kind of shoot, so good to know that the C100 can do a (carefully lit, undemanding) chromakey shoot unaided, and that an external recorder is still a useful 'Health & Safety' workflow (i.e. it will probably dig me out of poo one day).

Hopefully the stuff I shot will appear on the web in public soon so I can link to it.
 
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