[Per Holmes]

Hi,

Thanks for responding. I have some good news, which is that indeed Panasonic’s DVCPROHD decoder does not do any chroma filtering and Raylight does, so it looks much better in Raylight (see below). I should add, though, that NOT doing chroma filtering is not a bug per se, and I’m perfectly able to do my own chroma filtering in post. This is similar to the “Matrox Bug’ back in the DigiSuite days, which wasn’t really a bug, but more an omission, deliberate or not.

I’m quite happy with what raylight does so I think that’s certainly something to get.

The halo is not gone, though, just more blurry:

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

And here it is composited in Ultimatte. The keying consisted of selecting the backing color and then doing a single ‘Add Matte’ on her face to bring up the matte density. So not a carefully done matte, but with exact same settings as before.

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

I think that definitely the composite looks better with chroma filtering, which interestingly enough, Ultimatte wouldn’t do even when it was enabled and in native resolution (it has 4:2:2 / 4:1:1 / 4:2:2 compensation as a feature).

Still the halo is not gone. However, and this is very important, earlier today I took some pictures with my Nikon D70s, which also shows a little bit of a halo, even with sharpening turned all the way down. I have no idea what they do internally, or if it’s even important to Nikon to be able to completely disable the edge enhancement, so I don’t know for sure if that’s a clean signal. Unfortunately, I don’t have it here right now, so I can’t upload.

But what this means is that it’s probably true that with Detail and V Detail at -7, the HVX is likely not doing anything to the signal, edge enhancement wise. Regarding the halo, it may be a function of CCDs as such, as the signal IS analog at some point, and there could possibly be some capacitance causing it at an analog level. I also still haven’t analyzed the analog component signal coming out of the camera, to see if it’s a codec issue (but if it is, I would consider that a real bug).

In any case, I’m finding that I’m able to compensate for it quite a lot with the echo cancellation technique I’ve described in another post in this thread. And with light wrap on body parts that are over bright backgrounds, it starts to look like a real composite.

Thanks,

Per

[Per Holmes]

Hi Barry,

I can also assure you that the internet is full of people who get a halo on their HVX green screen footage. On a very regular basis, those people get answers from other people insisting that there’s no halo, uploading footage as proof that CONTAINS A HALO. Fascinating.

I’ve done about 60 separate tests of all combinations of Detail and V Detail settings between -7 and 0, and I can assure you that the halo only increases.

I was previously following the advice you apparently also have been given about -3 being the sweet spot, but that must have been one person’s perceptual feeling. I can say with certainty that -3 is not a sweet spot. It is simply more edge sharpening than -7. I’ll much rather add this sharpening in post, where I can control it. Again, -3 is not a sweet spot, even if that piece of knowledge has propagated over the internet and become ‘common’. I know for a fact that it has more edge sharpening than -7. I’ll be happy to show the pictures if it still matters.

If you’ve read my analysis and looked at the attached pictures, you’ll also know that -7 is in fact truly OFF for the edge sharpening on the LUMA signal. A BW version on a -7 shot yields no edge.

The term to describe this phenomenon is what I would call a Chroma Echo. I have since discovered a specific process that can remove a lot of it by essentially cancelling the echo. In a node-based compositor, I transform to YUV, on a side-chain shift everything two pixels to the left, and blend the U and V channel back ON TOP of the previous signal using what in Fusion is called a Minimum operator, which only adds signal back if it is equal or stronger. That echoes some green in the opposite direction.

This cancels the echo, but also creates a little bit of echo on other edges that weren’t affected as much to being with. A quick garbage matte makes the process more selective. And with a light-wrap or edge-shrink on the parts of the actor that are composited over bright background (procedurally controlled based on brightness), also works great as well.

These are hacks, but they are able to cancel out most of the problem.

As for the keyer, the halo is simply dark enough that Ultimatte considers it to be part of the person and not the green screen. I do get a little frustrated when it’s assumed I’m utterly inexperienced, especially when I’m being this meticulous and scientific about demonstrating the issue.

The problem is also in Primatte and Fusion’s Ultra Keyer.

And no change in lighting has any effect on the halo. I’ve done maybe 50 different lighting tests, front left, front right, side, other side, silhouette, hard light, soft light, up, down, you name it, I’ve tried it. Halo halo halo halo. In every situation.

Thinking it might be come analog capacitance in a DC filter coming right out of the CCD before the A/D converter, I’ve also tried to physically matte the green screen by putting paper in front of the lens so lessen the transition — maybe the circuitry was having trouble with 500 pixels of green before the first edge.

The halo only seems to lessen on edges that are very dark or black to begin with. But all that really means is that the halo blends with the black clothing to become perceptually invisible, it’s easily still there.

Everyone is always talking about how everybody they know is pulling perfect keys. I would like to see those keys. Maybe the actors have been getting an edge-shrink haircut to make it work. I want to see that uncompressed full res footage, only then can we truly and fairly discuss this halo.

Best,

Per

[Per Holmes]

Come on, you guys have to give me some credit. Everything is done at the absolute highest resolution.

Upload an uncompressed still of your footage, and I’m quite confident I’ll show you a halo.

Best,

Per

[Per Holmes]

Hi Jan,

I’ve done of 70 test shots with incrementally different settings of Detail and V Detail. It only gets worse with higher settings.

Per

[Per Holmes]

Hi Jeremy,

Thanks for responding! I haven’t tried that, but tomorrow when it’s brighter, I’ll bring the HVX and a green screen cloth into the edit bay and check it on the Mojo, which I believe can record uncompressed analog? I unfortunately don’t have a monitor in the house good enough to check it directly on a monitor. Unless I’m mistaken, the Avid Xpress Pro/Mojo combination can record uncompressed analog 480i.

But yes, I’d love to find out. I’ll post my results.

Cheers,

Per

[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

[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?

[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