To Jan Crittenden: HVX-200 Green Screen Halo Problem

[Nate Stephens]

Per,

Not to dodge your research. But years ago when using my old Sony M7, I had terrible fringing or halo. My only escape from it was to get the talent away from the Green screen as far as possible and to light the back edges of the talent with a peach or cosmetic color gell. I was getting to much green screen spill onto the edges of the talent, so I had to neutralize the green edges on the talent reflected off the green screen with a reddish / peachy color / or other color. And I do not have a big space. My edit and insert stage / green screen are located in a converted 2 car garage.. and it works…

I am getting the 200 this week. I hope I can get the same results at 1080. I will soon find out.

[Per Holmes]

But it’s not a spill issue. There’s a clear 2 or 3 pixel wide dark area OUTSIDE the person. Even outside of hair. It’s like a faint drop shadow. I could replicate it exactly by doing a proper key shot with a different camera and doing a 3 pixel drop shadow in Photoshop with Opacity set at 5%.

There have been many arguments made that this is either about the lighting or about the type of lens in the camera. But no lens I know can produce this effect, there is absolutely nothing wrong with the lighting, and a DVX-100 camera with Andromeda, which displays the signal coming straight from the A/D converter, shows absolutely no halo, as does no digital camera picture I take. So that rules out that argument. Natively, the signal is just fine. This is coming from somewhere down-stream inside the HVX-200, there’s just no doubt.

I think that people who are trying to argue that they can remove the halo with lighting are getting confused, thinking that their change in lighting is causing a solution. If the problem is some sort of errant DC filter that is inserted before the sharpness generator inside the camera, then their change in lighting will change the capacitance inside the DC filter, causing the halo to behave differently.

But lighting is not a solution, and neither is the lens the problem, because these same cameras, with an A/D converter tap do not show the halo, so clearly, neither the lighting or the lens or the CCD or even the pixel shift is a problem.

There is a DSP problem. Or, Detail -7 is just not absolute zero. Maybe Panasonic felt embarrassed about the native resolution and didn’t want people to see it completely unsharpened, I don’t know.

But something is wrong when a perfect green screen shoot, absolutely everything done right, produces a 3 pixel black border on one side in Ultimatte.

I absolutely insist that edge sharpening is not completely disabled in the HVX-200, even at the lowest settings. This is a MAJOR flaw, considering that Panasonic actively advertises how well the HVX-200 handles green screen.

I’ve communicated with people who feel like they’ve solved it in post, by making a bizarre 50 node tree in Shake that includes rotoscoping the halo. This is clearly not a solution.

I implore Panasonic to analyze this error. Zoom in on ANY green screen shot you can find on the internet (PNG/TIFF files) that is shot with the HVX, and you find the same halo. This is not one or two shots, this is hundreds and hundreds, and everything I shoot exhibits the same, even under perfect conditions.

Taking Detail to the lowest setting DOES NOT DISABLE IT. That effectively prevents you from doing green screen that you have any kind of pride in. I’m sure it’s fine for YouTube, but not for production.

I’m going to try to grab a component tab straight out of the camera and see if the signal is any different. If it is absent there, I guess the conclusion would be that this is perhaps an error in their DVCPROHD codec. But since the halo is there in all format, which is many completely different codecs, it’s probably not a codec issue.

Best,

Per

[Jan Crittenden livingston]

Hi Per,

If for some reason you cannot pull a good green green with the 200 then there must something wrong with the way you have lit the subject or have set up your camera’s menus. I have a freeze frame of a girl with blond hair flowing in the wind so that there are individual strands, and even those fine hairs are cut out without any of the artifacts that you mention. She is standing in front of a wall of fire. Now the setup on the camera was right out of the box with all of the defaults in place. The freeze fram looks fabulous.

So you should take another look at the way you have the camera set up, or the way you have lit the subject. It isn’t the camera causing the problem.

Best regards,

Jan

Jan Crittenden Livingston
Product Manager, HPX500, HVX200, DVX100
Panasonic Broadcast & TV Systems

[Nate Stephens]

Jan, can you post that freeze frame of your blonde girl chromakeyed over fire.

I should be able to use it to sleep better and encourage my co-workers that this P2 path is the right path that we are starting on this week.

[Nate Stephens]

Per,

This is sad to hear because I am going to pick up my new HVX200 this week.

What you discribe sounds just like the problem I had with my on line Prodigy switcher. No matter how much I tweak the chromakey clip and gain there was always “crust” green edge on the left side of the the talent. Then one day I got the engineer to visit, I showed him the problem, he scratched his head, studied his engineering drawings of his install and got out his trusty tweaker. And everything was Perfect… The problem was that the “hole” cut in the background was “out of blanking” (sync) with the keyed foreground. Once he fixed the “blanking” problem due to a cable being 3+ inches too long, everything was very pretty.

But if you are using Ultimate software and the computer, I have no idea how one would address a blanking error between the keyed foreground and the hole cut by the chromakeyer. And it smells like a blanking error, because the 3 pixel green crust does not encircle your subject on all sides. Why does it happen on one side and not the other.

Have you tried different colored background for your key color. Is the camera more sensitive to chroma green, than chroma blue, or even 100% white or black.

I am eager to hear the cause and the solution to your problem, too. Because by Friday we will have a HVX200 and hopefully soon we will have the 500 too.

Gosh, I miss the old days when there was always bad cable, or the missing engineer that the client didn’t want to pay for to blame.

[Vince Becquiot]

Per,

I have to agree with Jan. I have not had any issues keying with the HVX200. And certainely no halo. We always do a test on a white then black to find issues first. It was very much clean.

Our last location setup: Green foam based screen (10×20) was lit with 4 Cyc lights, near perfect line at 50 IRE’s on the waveform monitor. Talent 15′ from the screen. 2 medium chimeras and 1 back fresnel with some Rosco 3313 (Arri) on the talent. I could have keyed this in Premiere. (If you know Premiere’s keyer, you’ll know what I mean).

Tell me about your setup, maybe I can point at some issues.

Vince

[Per Holmes]

Hi Jan,

Thanks for responding, although I’m a little disappointed in your dismissive answer, as if I have no idea what I’m doing. So in this email follows various uncompressed PNG files that analyze the issue.

For all of this, these are the HVX settings, which I believe all will agree are the correct settings for green screen:

Resolution: 1080i/30p
Detail Level: -7
V Detail Level: -7

In addition, all of the following have NO BEARING on the halo, regardless of setting value:

Detail Coring: 0
Chroma Level: 0
Chroma Phase: 0
Color Temp: 0
Master Prd: 0
A. Iris Level: 0
News Gamma: Off
Gamma: HD Norm
Knee: High
Matrix: None
Skin Tone Dtl: Off
V Detail Freq: Thin

The subject is lit with banks of flourescent lighting at 5000K, soft all around the subject with a slightly stronger key coming in directly from the right. These lights are all about 4 feet by 2 feet, yielding relatively soft light. The side where the edge is occuring is FULLY LIT. There is no halo in the real world. Distance to green screen is about 15 feet, and the doll is standing on a ladder.

Here is a raw still frame as PNG, only stretched from 1280×1080 to 1920×1080 to correct aspect:

https://www.hollywoodcamerawork.us/hvx/barbie.png

As you can see, the edge is clearly there. It does not matter how the subject is lit, whether the key is coming in from the left, right, up or down, soft, hard, doesn’t matter. NOTHING I can do physically can make the edge go away.

When this is keyed in Ultimatte, the keyer understands the halo to be part of the person, not the green screen:

https://www.hollywoodcamerawork.us/hvx/barbie_comp.png

Don’t mind the hair detail getting a little blobby, I haven’t done much work on the hair. But increasing the matte density only INCREASES the appearance of the edge, so please criticize the keying job appropriately. This is a technical test.

Interestingly, the problem is in the color sampling. If the image is completely desaturated, the halo disappears:

https://www.hollywoodcamerawork.us/hvx/barbie_bw.png

I will therefore agree that the issue is probably not caused by THIS PARTICULAR sharpness generator. With Detail and V Detail at -7, it appears that the luma signal is not being touched. However, the chroma signals still are. In a YUV conversion, the halo is clearly visible in the U and V channels (but not in Y).

The edge appears most to be a sort of horizontal echo in the U and V channels, which gave the idea to cancel the echo. So I built a composite that converts the shot into YUV, then does a side chain that shifts GB (UV) 2 pixels to the left, and then merges them back on top of the other signal using a Minimum operator, which will only increase the dark green around the edge. This works:

https://www.hollywoodcamerawork.us/hvx/barbie_corrected.bmp

(quick edit, the previous PNG export from compositing had changed gamma. This BMP file is fine).

As I said, this works, although the left side of the image has less halo problem to begin with, which means that the halo problem is increased slightly on the left side. From everyone else posting about this halo issue on the internet, in all shots, the halo is coming from the right just like mine, except one shot where the halo was coming from the left, presumably shot with a 35mm converter and flipped.

So a quick and dirty garbage matte applies the correction to only the right side of the character (we’re now in NTSC SD, but it doesn’t matter, the halo is equally visible at all resolutions):

https://www.hollywoodcamerawork.us/hvx/barbie_corrected_comp.bmp

(Edited again to upload BMP file, apparently PNG export from Fusion has wrong gamma).

I can live with this workaround, and whatever problems remain can be solved by doing a lightwrap or edge shrink on areas that are over bright background (the halo is most visible on bright background).

But there is still an edge enhancement algorithm BEFORE the normal Unsharp Mask, and whatever it is, it isn’t turned off. Many have argued that this is simply the nature of these semi-pro DV/HD cameras, but I offer as proof a shot done with the DVX-100 Andromeda upgrade, grabbed from the Reel Stream website. This (now unavailable) upgrade grabs the signal right out of the A/D converter, before the camera has had a chance to touch the signal.

https://www.hollywoodcamerawork.us/hvx/andromeda.png

No halo. Even on a DVX-100. Isn’t that interesting?

[Matt Gottshalk]

“No halo. Even on a DVX-100. Isn’t that interesting?”

Please. You are being highly disingenuous .

That is, as you mentioned, a grab from the now defunct Rel-Stream modification to the DVX-100, which has absolutely NO bearing on this discussion at all.

The HVX at DVCProHD and DV50 has exactly the same color space as a Digital Betacam camera: 4:2:2

I any many other have pulled fantastic keys shooting on properly lit green screens.

However, I think you may be asking for too much from a 1/3″ chip camera.

[Per Holmes]

Hi Mark,

Thanks for responding. I don’t think it’s true that such a frame grab has no bearing on this discussion. If the issue is whether or not any image processing is taking place in the DSP section of the HVX (or DVX), then I think it is highly educational what the signal looked like going in.

Granted, that frame grab is not a fantastic green screen. But there’s no halo.

I still think that’s interesting.

Best,

Per

[Jeremy Garchow]

Per, is this footage from the P2 card or have you captured off of the component output?

I am wondering if it’s the codec, not the camera.

Jeremy