Green Screen AF100 footage - Test shots

[PaPa]

Hey gang,

posted this in the AF100 section but thought maybe it would get a little more attention here to all of you who have a good level of experience with after effects and keylight.

I shot my lady friend in front of a screen, put the file up in AE with a background i found on the web to do some basics tests. I've watched October Black's tutorials but for the life of me i still can't get a key that i'm really happy with.

If any of you are willing to take a stab at this and then post your findings and methods, I would be greatly appreciative. And i know it would be a great learning experience for anyone who is dying to learn how to use the tools in AE to create some really nice keys.

Here is the link to the footage:

http://www.zshare.net/download/91350701522c8984/

There are 6 tests going on. Each clip has about a 5-8 second duration so the file sizes are nice and manageable.

Shot 1: Falling hair
Shot 2: Red ball
Shot 3: Orange ball
Shot 4: Green ball
Shot 5: Clear glass of water
Shot 6: Opaque jug pouring water into glass.


Here is the background that I'm using at the moment:
http://www.reeces.com/img/kitchen-02/kitchen-02_b.jpg

So give it a go and let's see how we can use this footage to get the maximum results. I'm very eager to learn and have been spending hours trying to find the best way to get something that is believable.

 

[PaPa]

I take it no one is interested to take a stab at these? I know tons of people here would be very anxious to learn a thing or two and if you have the time, would be a very big help to those of us learning.

 

[j1clark@ucsd.edu]

I take it no one is interested to take a stab at these? I know tons of people here would be very anxious to learn a thing or two and if you have the time, would be a very big help to those of us learning.

I looked at them briefly... one comment on the 'transport'... some people may not like going to a site that has advertizing spamage to get the media...

Aside from that, you did pick some of the usual problem children of keying... fine hair... clear glass half full of water... pouring water... etc...

Some of these things there are a couple of ways to deal with, and seem to always involve 'work'... for example, perhaps the glass/water shots would be better done with some rotoscoping, even if one is keying eventually to narrow down which area gets what type of keying.

The hair thing is problematic because of the fineness and course rotoscoping is difficult as well...

So, that's my thoughts at the moment...

 

[PaPa]

** EDIT **
I should be clear and say the background is not meant to match the footage, but is there solely to bring forth the shortcomings of the key and let the flaws stick out. I found that gray in the BG was more forgiving.

Yeah, i definitely wanted to shoot things that I could forsee giving keying the biggest problems. Heavy motion blur, fine details, opaque objects. I felt like learning how to key those elements would give a huge advantage and facilitate anything I wanted to key in the future. Were you able to give any of these a shot?

Things I would do in the future: Have a broader backlight but also softer to cover more of the edge area. Bring a little chroma back in camera to get a better green and lower it's exposure by around 10 IRE. Anything involving heavy motion blur i would up the shutter speed slightly to reduce the transparency of motion. I would also try and arrange wardrobe to have something that has less patterns/gradations because what she is wearing may or may not be taking up a lot of the cameras bit rate. There are pockets of lighter and darker and i can see it's giving 8 bit some trouble.

With those things now in my head I will go back and try a few more tests. But I think I might be on to something which is encouraging since the key can only get better.

 

[j1clark@ucsd.edu]

From this clip, one of the issues is that of 'light direction'. the background plate looks like it was shot with one light pretty much from the camera POV.

One thing you should think about for 'matching up', is to shoot a reflective ball (mirror like) and a 'defuse' grey ball in the location you are eventually going to place your greenscreened subject.

Then in the greenscreen session, match up the lighting with what you find by inspecting the lighting targets. (Same principle for creating CGI environments, but there one takes the greenscreen lighthing
and places the virtual lighting appropriately...).

In the example clip, I see a top light, and edge lighting, but in the plate I do not see the 'apparent' lighting sources.

If you don't have the ability to get lighting info directly from the shot... like getting stock photos... then an analysis needs to be done to reconstruct what you think the lighting was, and light the greenscreen subject accordingly.

 

[PaPa]

From this clip, one of the issues is that of 'light direction'. the background plate looks like it was shot with one light pretty much from the camera POV.

One thing you should think about for 'matching up', is to shoot a reflective ball (mirror like) and a 'defuse' grey ball in the location you are eventually going to place your greenscreened subject.

Then in the greenscreen session, match up the lighting with what you find by inspecting the lighting targets. (Same principle for creating CGI environments, but there one takes the greenscreen lighthing
and places the virtual lighting appropriately...).

In the example clip, I see a top light, and edge lighting, but in the plate I do not see the 'apparent' lighting sources.

If you don't have the ability to get lighting info directly from the shot... like getting stock photos... then an analysis needs to be done to reconstruct what you think the lighting was, and light the greenscreen subject accordingly.

I really truly do appreciate your feedback and comment, but between me and everyone else here, the background plate was not intended to match the shot, it was used solely to give me a nice visual between my subject and the key. I found putting neutral gray in the BH made it harder to see imperfections. But puting just anything there let me see more of the flaws. I guess I should have stated that in the post. My bad.

Thank you though.

 

[PaPa]

Did another quick test last night. I've been asking around a few friends that do compositing and they are trying to drill in my head that there is only so much you can do with 420. Based on their opinions, there is nothing wrong my the shots, but the limitations of the codec.

Is this true? He saw this still and assured me that had this been done with a higher bitrate and more importantly 422, the key would be substantially easier and more believable, especially when it came to motion blur and motion in general.

Another question, if this is the case and there is limitation to the 420 color space, does this mean that the codec is limited in such a way that requires shooters to create a decent amount of backlight around the subject to help pull a key?

I started off doing closeups and noticed the reason I'm having a hard time getting a good key was because my depth of field was too narrow that the little hairs on top of my head further back were slightly out of focus and were getting lost in the key. I've been having more success with medium and wide shots simply due to the lack of fine detail in the edges. I thought this might have been backwards but still a great learning experience. Shallow depth of field is really your enemy here it seems.

 

[handsome pete]

The wiki page on chroma subsampling will give you a better idea of why 4:2:2 would be better. Much easier than trying to just explain it here at least:

http://en.wikipedia.org/wiki/Chroma_subsampling

Your friends are right in that 4:2:2 would yield better results, but most prosumer cameras these days aren't 4:2:2 capable (without something like the nanoflash at least). So more often than not you won't have the luxury of working with that footage. 4:2:0 does have its limitations which means it's all the more important to get everything else right. That's not to say you can't pull a solid key, but it will take more work both on the set and in post.

 

[PaPa]

Yeah. Maybe I should stop wracking my brain and accept there is only so good a result I can get. I mean, I look at this footage and really don't think there is a way to make it much easier for my keyer. With a deeper depth of field ( i think i was around F5.6- F4 ) and a few feet back from a 35mm lens, I kept ther hairs in the back of my head in focus, a little back light and all the hairs were kept in without looking cut out or mushy. Now it's just a question of practice and learning how to deal with motion blur.

I'm going to try upping my shutter from 1/48th to maybe 1/60th- 1/75th and then perhaps adding some motion blur in AE to compensate. Definitely fun experimentation.

 

[j1clark@ucsd.edu]

Yeah. Maybe I should stop wracking my brain and accept there is only so good a result I can get. I mean, I look at this footage and really don't think there is a way to make it much easier for my keyer. With a deeper depth of field ( i think i was around F5.6- F4 ) and a few feet back from a 35mm lens, I kept ther hairs in the back of my head in focus, a little back light and all the hairs were kept in without looking cut out or mushy. Now it's just a question of practice and learning how to deal with motion blur.

I'm going to try upping my shutter from 1/48th to maybe 1/60th- 1/75th and then perhaps adding some motion blur in AE to compensate. Definitely fun experimentation.

The Wife and I have done some keying for her projects, and fortunately these 'fine details' such as hair, have not been an issue, since I can't afford a camera that does 4:2:2 sampling... So, I have to live with what I can get. What that does mean, is I'll probably not be doing Blonde girls with long hair flopping around... there's the Wife to consider anyway... but no significant motion, etc., since as you raise the shutter speed, you need to raise the light level as well...

Fortunately most of the keyed shots we anticipate I may be able to position things so that 'keying' is on reasonably sharp edges...

The alternative if rotoscoping, which also has 'motion' issues, fringing issues, etc... but for some work, may be better than the automagic of keying.

Another thing I've noticed on seeing 'pro' keying setups, is they will light the 'greenscreen' with a light that has a green gel on, to increase the 'greeness', along with appropriate flagging to limit any green light on the subject or set. Some of your shots seemed to have the greenscreen a bit 'dark', and could also add to the fringing of the key.

 

[PaPa]

The Wife and I have done some keying for her projects, and fortunately these 'fine details' such as hair, have not been an issue, since I can't afford a camera that does 4:2:2 sampling... So, I have to live with what I can get. What that does mean, is I'll probably not be doing Blonde girls with long hair flopping around... there's the Wife to consider anyway... but no significant motion, etc., since as you raise the shutter speed, you need to raise the light level as well...

Fortunately most of the keyed shots we anticipate I may be able to position things so that 'keying' is on reasonably sharp edges...

The alternative if rotoscoping, which also has 'motion' issues, fringing issues, etc... but for some work, may be better than the automagic of keying.

Another thing I've noticed on seeing 'pro' keying setups, is they will light the 'greenscreen' with a light that has a green gel on, to increase the 'greeness', along with appropriate flagging to limit any green light on the subject or set. Some of your shots seemed to have the greenscreen a bit 'dark', and could also add to the fringing of the key.

I'm not worried about the light level. I was between F4 and F5.6 at ISO 400 with ND 2 or 3 on. More light wouldn't cause me problems.

Yeah, good edges are important I'm seeing. I simply assumed from the beginning that if i have a good bakclight i wouldn't get any issues, even if things were slightly out of focus. This was clearly not the case.

I guess Rotoscoping will be something to learn a little further down the line, but for now I want to try to do some practical tests with the results I'm getting out of this. You know, little short scenes with a plate.

I'll definitely check out adding a green gel to the lights, makes perfect sense really, more saturation, but thi does mean that I can't benefit from having the light also shine around my subject slightly like i've been doing. It actually helps out quite a bit!

Lol I've been told my screen is too bright, too dark. I'm finding under 35 gives too much compression noise and over 50 to be too bright, but somewhere in between seems quite solid. What are your experiences with green screen IRE?

 

[x_WOrPIG_x]

I'll take a stab at this this weekend. How many lights on your green screen? What temperature are they?

You really have to make sure your screen is evenly lit as possible.

Made these two web commercials with gh1 / gh13. I used keylight in AE.

http://www.youtube.com/ymcasudbury

 

[PaPa]

Hey Ryan,

here is the general setup going on for the screen. All daylight temp:

The screen is quite evenly lit, and almost perfectly around the subject which makes the keying not too shabby. I got it exposed a little under 40 IRE.

This is a still from my latest test. Everything is, actually very acceptable to my standards when there is little motion. But once the arms start swinging, well.... Let's just say I'm thinking of upping the shutter speed and then if need be adding a little motion blur in post. I'm guessing that tends to be a trend with these 420 cameras:

I lost a little detail around the side of the hair but with a bit of a kicker around the side that problem would vanish me thinks.

The only issue I'm having right now is that the key tends to bias the highlighted hair a little too magenta.

 

[PaPa]

Anyone know why exactly this magenta coloring is happening? There is definitely no spill on the hair as they are being lit seperately, and the magenta is kind of strong when put against an actual plate. Backlight too strong?

 

[PDR]

Anyone know why exactly this magenta coloring is happening? There is definitely no spill on the hair as they are being lit seperately, and the magenta is kind of strong when put against an actual plate. Backlight too strong?

There is probably micro amounts of spill, and you'll probably get small amounts of shifting where there is overlap in the transition areas like edges. When you subtract green you get magenta

I think you can modulate what keylight "thinks" is spill by adjusting despill bias . I know keylight automatically applies an antispill calculation

 

[PaPa]

I tried that, but I'm still getting a magenta contour around the edges of the hair. Very odd... Perhaps my backlight is too hot and brings the hair too much towards yellow so it confuses the key.

 

[PDR]

That's probably what's going on

I thought you were just one of those "cool" kids and went to the salon to get some highlights done

You can try multiple passes and different keys. e.g. do a separate key for that part of the hair

 

[PaPa]

So you think the rim light was too hard and over exposed a little? I mean, sometimes i see keys that have quite an aggressive backlight, but they are generally softer and broader too.

Multiple passes I'm guessing involves doing a track matte, not something I have learned yet but definitely will get around to it once the basics are in the bag.

Strange though. The hair on hte side of my head has basically no rim, and it doesn't suffer from the magenta, but it doesn't have as pronounced edges as on top, which is maybe a bit too bright. This is such a subtle art...

 

[oneinfiniteloop]

You're getting decent results. Some general thoughts…

You can rim them with magenta or orange to help create more color contrast to make the key easier. You'll have to color correct it out in post, but that's generally not too hard.

Create as much separation between your talent and your screen as you can. I personally think you're IRE on the screen is a bit low, I generally like to light it at 50-70 IRE depending on the camera we use. Obviously the brighter the screen the brighter the spill, but separation helps with that.

Turning up your shutter speed and adding the motion blur back in post will help a lot. Also, turning your camera 90 degrees on it's side will be helpful for the type of shots you've done for your tests. This gives you more resolution and a better key.

That top light on the hair is kinda odd. I know you're trying to get separation, but maybe bring the back light around to the side and behind a bit, then bring your fill back some too. Right now you have a really flat image without a lot of shape. This should help create some separation around all the edges of your hair without that big spot look on top.

For keying in post, use two instances of Keylight, one for edges and detail and another for the core matte. This way you can retain edge detail and then use the core matte for the inside. Essentially you choke the core matte in so that it doesn't affect the edges and use the edge matte to keep details and tweak it a bit to get the best results. With any keying there is always going to be some level of roto and color correction and working with edges is the hardest part and the name of the game.

 

[PaPa]

Great suggestions.

Rimming with orange or magenta, how exactly would you then fix this in post? Right now it seems as though my backlight is causing my brown hair to go slightly yellow making keylight think that it's green spill and turning the edges magenta. Been toying around with the despill color and edge correction but can't quite nail a good result.

Ire of screen too low? I'm getting mixed up here, some are saying around 40, some say higher.

I've seen this turning the camera 90 degrees in photos but haven't tried it yet. I'm wondering how exactly it would give me more resolution? Wouldn't I just be getting a longer image? Or is it because I'm wasting less on the sides and filling more of the frame? I wonder if the af has side mounts behind the handle as that would be the only way I could mount it sideways.

ideally for my backlight I would be using my fluorescent lights instead of these hot spotters which should be softer and cover more surface area evenly.

I've been using two instances of keylight for everything. Much better results that way.