Matchmove comp thoughts and advice?

[chazfest]

Hi,
I'm nearing the end of my comp now and I'm looking for all the juicy advice I can wrap my ears/eyes around

I did everything in NukeX including the camera track. I then did a sky replacement with a couple of keys and a card, added the bullet hits and holes on the road and added a cheeky explosion just for fun (perhaps overkill as there's no cause of explosion yet, unless I add in a bouncing grenade or similar thrown from off cam??)


Just a quick pre warning/foreword; I'm entirely self taught when it comes to compositing and matchmoving etc, and am keen to pick up all the advice I possibly can, so I'm sure this'll be far from perfect, but that's exactly why I'm here, to listen and hopefully improve upon my skills with the help of others
I'm a video editor by profession with a huge passion for VFX, and I hope to move towards a compositors role in the future when my skills increase far enough.

Huge thanks in advance to any who can spare the time to look and feedback on this one

[dcompz]

Hey,

This is looking pretty good so far. Very nice work since it sounds as if you are just getting into this type of stuff.

First off, the track seems to be sticking well. The sky replacement has a few issues, however. I'm seeing some blue fringe in the background trees and some popping/edging issues as the smaller tree branches move over the space between the buildings on frame right. Overall, you need to work on some of the keys a bit more. Besides the edging issues I mentioned, quite a few of the thinner objects like the lamp posts are being eaten into too much and in some cases are flickering out entirely (see the post in the left background between 0:03 and 0:04 and the post in the right midground between 0:04 and 0:07 as examples).

The bullet hits are working well. If anything I'd say the blacks might be very slightly off compared to the rest of the plate.

The explosion needs more contrast to match the plate better. Again, I think the blacks need to be pushed down a bit. I'm also missing some more cast lighting and reflections on the objects around it (the traffic signal and parked cars on the right for example) which would help to really tie it in.

My final note would be that the vignette might be a touch heavy but that is more of a personal preference.

Hope this is helpful. Keep up the great work!

- Dan

[chazfest]

Thanks for the feedback Dan! That's really awesome!

The 2 keys I pulled for the sky weren't great, I must admit. I'll start from scratch on the sky and see if I can get it cleaner. I actually ended up using 2 Keylights :/ purely due to my inability to get the luma keyer working! I'll look into that on The Foundry's site to see if there's any pointers as I'm thinking the luma keyer might be a safer bet? I see what you're saying regarding the crushing of the lamp posts and tree branches too.

The bullet hits colour correction isn't spot on like you say, so I'll work on matching the plate more closely.

Regarding the explosion though, your ideas sound perfect, and I know that's how things would occur in the real world, but I've no idea how I'd go about adding reflections to the scene. I thought Nuke didn't handle reflections well? Perhaps I misunderstood. Either way, if you've any tips or ideas for how I might start experimenting with that, I'd be eternally grateful It's actually something I've wanted to do in the past but just never found a way to do so.

And the vignette? You're probably right I'll lower the intensity a little.

Thanks again for all your help, its given me a little more direction on this shot now. I'll be reposting shortly.

Chaz

[dcompz]

Depending on the original plate, Keylight could work just fine. Of course everybody has their favorite keyer but you could probably get decent results with just about any route you take. For quick results, I usually just use the a combination of Keyers but some people swear by the IBK keyer. The point is different ones may work better in some scenarios but if you are really comfortable with a certain one you can get comparable results. The Foundry site and Youtube channel definitely have some videos covering keying/sky replacements so I'm sure it would be worth a look.

In regard to the bullet hits, it may also have been the youtube compression. They were just catching my eye since the blacks looked slightly lifted compared to the bike next to it.

For the explosion, your easiest bet would be to try and fake some of the lighting and reflections. It doesn't have to be real-world accurate but you could use some soft masks to add some "light" back over certain objects as the explosion goes off. Since you have a 3d camera track, you can put in some rough proxy geometry for the pole and cars. If you wanted to really get into it you could put one of the shaders that supports reflections like Specular on the geometry but that can start slowing your scene down. Nuke reflections aren't the greatest by any means but you can get something to work with. I would just start using cards/geo with the explosion and match them to the objects I wanted to reflect on, then try to blur or warp it around until it looked believable and the same for the cast light.

The vignette thing really was more of an opinion. If you like it then definitely leave it as it is. It's just one of those effects like lens flares that you see a lot and people tend to go overboard with so subtlety is always key. I can only really speak for myself here, and I'm not saying this is the case with this specific shot, but in a scenario where you were going to use this on a demo reel, you don't want somebody saying "Oh man, another lens flare/vignette/any other commonly overused effect". Done tastefully, any effect can work well though.

Happy to help. I look forward to seeing future versions.

[chazfest]

Interesting to hear you say that, cos after having gone through the Primatte, Ultimatte, Keylight and IBK videos on The Foundry's site, I still feel much more comfortable with Keylight. Not to say I don't and won't experiment with others, but still, it would appear my 1st choice is Keylight.
Quick question regarding multiple keys, could I just combine them with a merge node set to alpha? And am I right in thinking that, in the case of Keylight, I'd switch it to 'Intermediate' in the drop down menu to allow me to combine it with multiple keyers further down stream?

Regarding the explosion, I've made a copy at -90 degrees/laying on the floor, and added volumerays and a huge edge blur and glow to it, then lowered the opacity with a grade node, so hopefully it'll roughly follow the overall motion of the explosion as it happens. I'm also going to have a crack at what you advised with the cars and take a card, place it at the side of a couple of cars in nearest proximity and deform and texture it with a subtle glow, perhaps again linked with the original explosion shot?

Decisions decisions

[dcompz]

Sorry to just get back to this. Regarding your keying question, yes you can merge two keys that way. There are quite a few different ways to combine them depending on what result you need. A ChannelMerge would probably be easier simply because it already defaults to alpha assuming you want to keep the entirety of both keys. In a lot of cases, you might just want a small area of the key for a certain detail and the KeyMix works beautifully for that since it allows you to set a mask for the area you want to blend but really you can use any of the merge nodes with some rotos.

As far as the Intermediate setting on the Keylight, I believe that would be the correct output. Personally, when I key I prefer to keep all my keyers, rotos, etc. off to the side in a separate stack so I never really worry about the rgb channels and then I copy the the alpha back in to the image stream. Visually it helps me keep track of stuff and also gives me more control over spill suppression.

Sounds like you are on the right track for the explosion. Ultimately, it will just be about what looks right/good, not necessarily what is completely accurate. Fire/explosion type stuff is fairly forgiving, especially when you can add motion blur like your shot. Just needs to feel like it is interacting with the environment and you are good to go.

[Steinz]

i think the track for the explosion just goes off abit at the end , im seeing it slightly slip left

[Steinz]

on a more subjective note , considering the size of the 'hits' , would they not maybe leave (larger) craters / marks on the road. the hits you've gone for suggest quite an impact as opposed to ricocheting off etc

[j2m2mi2]

hi first of all i would like to say that your shot is well, but u need to do some fine tuning with bg replacement & as dcompz said work with the detail part of reflections & bullet hole details on the road. rest is fine.