I am trying to record my daughter for some videos but found some flickering artifacts on her shirt. She is standing in front of a green screen. For lighting I have 2 4ft fluorescent light boxes standing vertical to light the screen, I have 1 light box backlighting her that is diffused CFLs, and they 2 more diffused CFL light boxes in front and slightly to the side. I found that the flickering on her shirt happens with either type of lights. I am using my Sony alpha77 to record the video in the AVCHD format. I am processing the video using Adobe After Effects (2017 version).
I was wondering if anyone could help me out with how to get rid of the flickering. I have tried to reduce the shutter speed on my camera but the flicker is still there.
Here is a link to the video.
+ Reply to Thread
Results 1 to 12 of 12
What bitrate / recording mode ? Always use the highest bitrate / quality available
What does the original footage look like ? Does it exhibit the same problem , or to the same extent ? Or does this only occur on youtube, or prior to youtube, or only after keying ?
Did you use keylight in AE ? It's possibly from the spill suppression or incomplete key (not a solid core matte) . The lighting is too bright and I'm guessing you also likely had some spill. Those flickering artifacts are common with keylight's internal spill supression. You can see it in the hair edges as well . If you can't reshoot, you can disable the keylight spill suppression by passing through using keylight's "intermediate" mode, and use another spill suppression method such as "advanced spill suppressor" after keylight
Thank you for your quick response. On the camera we set the mode to AVCHD 60i/60p at 17Mbps, 24Mbps, and 28Mbps and I saw the same flickering artifacts for all of them. The original footage did show some of the flickering, but not to the same extent. The flicker was more noticeable after using Keylight in AE. I tried your suggestions for the spill suppression and it really did help. I found two that Key Cleaner and Advance Spill Suppressor did clean up the flicker on her shirt, but now there is a green hue at the edges of her red hair that I am having issues getting rid of. Would you happen to have an idea on how to reduce the green around the hair without losing too much of her hair?
The lighting is bright, and I will look at adding something to diffuse the fluorescent lights hoping that will help. Also I did lower the exposure on the camera but the flicker was still there.
Again thank you so much, I am new to green screen work and I appreciate your advice.
Generally you would do a multipass key, or multiple keys. There are many free tutorials on youtube and vimeo and similar sites. The general idea is 1 set of settings cannot cover everything ideally, even if you have perfect studio lighting because there are slightly different "shades" of green, different characteristics of light absorption. If you take a closer look at the youtube video, the hair looks cut off, and a bit unnatural - normally there would be fine stray strands, that sort of thing. Basically, you need partial transparency at the edges to preserve fine edge detail . Similarly , if a certain part like hair edges need attention or specific spill suppression you would apply it there only with compositing. So the typical approach is work on a solid core matte, then one or more additional layers/keys to preserve edge detail.
If you want to upload a small native sample, I can take a quick look and see if there is anything else or if there is a "quick" way to handle the spill. But a big problem is the bright lighting/overexposure. You're actually clipping on parts of the face and left arm. That exposure generally means you're going to have to do more work than you should really have to. The better the lighting, the less work you have to do
Also, since you said the "original" had a bit of flickering - that is abnormal, and the pattern is inconsistent with a shutter / electrical mains frequency mismatch, and you shouldn't get that at 28Mb/s on a mostly static scene - so that's another reason to take a peek at it - there might be something else additionally going on
Last edited by poisondeathray; 20th Nov 2016 at 21:52.
I loaded the original footage (https://youtu.be/pSx6dzt-B84). There is a hot spot on the left side due to the back light being closer than I want to the screen. Unfortunately I am limited by the space where I am filming. I will definitely look up the videos on the multiple key usage, thanks again for the advice. If you have any issues with the videos please let me know.
Youtube re-encodes everything, so you can't tell if some of the problem(s) were from youtube or something else . If you can upload an unprocessed, original sample clip from the camera it would be better. You can upload directly here, or free hosting sites such as zippyshare.com, sendspace.com , mediafire.com, etc...
The accentuated noise with keylight spill supression is a known issue - but I'm wondering if something else is adding to the problem. (For example, if compression artifacts in the original source are adding to the problem, there might be some manipulations you can do pre -key to improve the results)
The clip does have a bit of noise and all effective spill suppresion methods will accentuate the noise to some extent , some more than others. But the main problem is still the overexposure/lighting. If you improved that, you wouldn't have as much spill, and you could probably get away with keylight and it's internal spill suppression alone
The other thing you want to look at is the quality of the core matte. View keylight in screen matte mode. The centre core are should be solid white. If you have various shades, maybe grey patches - that's an incomplete key and that can add to the noise as well. (That's basically what people do for multiple keys anyways; they make sure the core is sold, shrink the matte, then work on the edges)
When you pass keylight in "intermediate result" view, then add another spill supressor such as advanced spill supressor - that should zap any remaining green left, even in the hair. Earlier you reported green still in the hair - that's not what I'm seeing so I'm wondering if you might have done something differently?
But anyways, one way to tackle the flicker/noise issue is to apply a light denoise, either pre-key or post key. The side effect of denoising is it makes the footage softer, so you have to use judiciously. If the noise issue primarily affects the black shirt, pants only, you could apply it through a rough mask , or luma matte isolating dark values, so as not to unnecessarily soften other areas
The MOV you uploaded uses PNG in MOV. FYI, for future reference you could have just uploaded the original AVCHD clip, it would be ~30x smaller. A free utility to cut transport streams is tsmuxer
Thank you for all of your advice. I was able to change up the lighting and found a better setting on the camera that results in less flickering artifact. I also followed your advice with the multi-key and was able to clean up around the hair and what not a lot better. Now about the only thing that is still an issue is the area under her arms when her arms are closer to her body. At those points there is what looks like a white highlight/outline. Would you have any suggestions for getting those taken care of?
When arms are close to body, but not touching, there should be "holes" ("arm pit holes" for lack of better words) where the green screen shows through pre-key. Correspondingly, post-key there should be alpha channel there, so the chosen BG shows through
If you're seeing a white outline surrounding the periphery of the subject anywhere - it usually means you matte is extended too far - you need to choke the matte or use different settings, or some combination of keys / compositing . But if you choke it too far, you errode and eat into edge details
Look at her left arm. Every time I've used shrink/grow or choker or increasing the black matte, I am losing other details. The edge where it is white was green before suppression. If I select it by itself then it will pull color off of her. I was wondering if there a better way during filming, i.e. back lighting, that could reduce or get rid of this?
If it's just a few parts, I'd probably just do some quick rotoscoping/masks to fix it, maybe even rotobrush depending on what her movements were like. If it was quite a bit of footage, I would use multiple keys/ compositing
But for shooting, backlighting might help a bit (but if not carefully done it can make things worse), as will increasing distance from the screen will help if you have room in your setup. Most people also tend to aim for exposure on the darker side to minimize the spill; you can color correct and grade afterwards.