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Cinealta - Greenscreen Questions


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#1 Matt Workman

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Posted 08 April 2007 - 10:57 PM

Hey,

I have a cine-alta music video coming up and the bulk of the video will be greenscreen. We are shooting with Digi Primes which should be a good experience.

- What IRE should I expose the greenscreen at? We should have the panasonic 17" HD monitor with the waveform and I'd like to keep the green screen at a consistant IRE range if possible.

I've done plenty of greenscreen shoots on video, but not with a waveform or the ability to control the lighting. I would guess that I usually exposed at 60IRE, but I have no way of really knowing.

I'm interested in your input and experiences.

Cheers,

Matt
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#2 Brian Dzyak

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Posted 09 April 2007 - 05:22 AM

Hey,

I have a cine-alta music video coming up and the bulk of the video will be greenscreen. We are shooting with Digi Primes which should be a good experience.

- What IRE should I expose the greenscreen at? We should have the panasonic 17" HD monitor with the waveform and I'd like to keep the green screen at a consistant IRE range if possible.

I've done plenty of greenscreen shoots on video, but not with a waveform or the ability to control the lighting. I would guess that I usually exposed at 60IRE, but I have no way of really knowing.

I'm interested in your input and experiences.

Cheers,

Matt



Your zebras are a defacto way to determine IRE as well. Mostly, you'll find a rental camera preset with 70% zebras, so if you've used that in the past, it's a starting point for your exposure.

That said, assuming you have the freedom and luxury of space and resources, you can probably get away with finding your optimimum stop for the foreground action then lighting the green to that. Assuming that you want the key to be somewhere in the range of 40% to 70%, that would help determine where you'd put the green. For what I do, I'm generally at the mercy of my light kit, so I rough the green in first, find my key stop, then tweak both from there a stop or two either way until I find the balance that works. Generally, I aim for a key around 50% or 60% and underexpose the green about a stop or so from that.
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#3 Michael Nash

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Posted 09 April 2007 - 04:04 PM

Close to 50% usually gives you the fewest problems. Just keep in mind that if you expose the green screen too bright (over 70) you actually lose a little saturation; underexpose too much (below 30) and you can start to get noise in the matte. 40-50 usually works well for most applications.

Besides, it's usually easiest to see the evenness of the green when it's close to a 1:1 exposure ratio with the foreground (not that you should light the green exclusively by eye). If the green is significantly brighter or darker than the forground you might not notice problems right away.
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#4 Matt Workman

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Posted 10 April 2007 - 04:46 PM

Hey,

Yeah on my low budget stuff all we had was two 650s with diffusion and we couldn't change them if we wanted to. This shoot has a little more room to breath.

Keeping the IRE around 50-60% sounds pretty good. Assuming 18% grey is about 35 IRE right? What do you usually expose the green at for film? At key or 1 stop over?

Thanks for the advice.

Cheers,

Matt :ph34r:
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#5 Michael Nash

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Posted 10 April 2007 - 05:38 PM

The IRE value of a properly exposed gray card will depend on your overall gamma setup, although 35% sounds pretty low. The idea is that an 18% gray card should come up as 50% on a waveform monitor -- but since tonal reproduction in video cameras is far less linear than film, you usually don't want to expose it that way. 45 IRE is a common "target" for gray in HD, but that highly depends on the overall gamma curve and how you plan on changing/displaying that image later. For example, typical SD video gamma for display on television often puts it up at 55%.

http://www.cinematog...php?t12648.html

http://www.cinematog...nToIREValue.htm

Just think of 50% as a reference point. In camera, above 50 your contrast starts to steepen and you lose color saturation. Around 50 and below your contrast starts to flatten out, and you optimize saturation.

It's all about getting a good, solid green that easily separates from your foreground subjects. For video I try to put it at 45-50% (as per the Ultimatte instructions for the post I'm often using). For film I follow a similar approach, usually one stop under or no more than key level. As for 60 IRE I've never gone that route, but typically you don't want to overexpose the green, just to avoid potential problems (green spill, loss of saturation, etc.) The truth is there is usually an acceptible margin of error, you're just trying to minimize the problems the post people might have to deal with.
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#6 Matt Workman

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Posted 10 April 2007 - 08:06 PM

Hey Mike,

Thanks for the lesson, I see you've had to explain this before. Bad DP for not searching thoroughly enough, :(

I can definitely see where shifting your gamma in a high contrast situation would help but I still would be hesitant because of the other artifacts, mainly in chroma that happen. Shifting the knee to gain latitude usually desaturates the highlights which is a fine line to walk especially on set.

With this information I will most likely rate the 18% grey at 50IRE. I will also be effectively lighting the green screen @ stop, or 50IRE. It seems safe to err on the side of 35-50 IRE because the chroma isn't effected as much as if I erred towards 50-75IRE.

This sounds like a good place to start anyway.

Cheers,

Matt

SIDE NOTE:

I am inexperienced with using the Varicam/Cinealta paint options and would only dare use them if we had an DIT on set. Should I be more bold with experimenting or does the "neutral negative for post" mentality make sense?

What is the film equivalent of shifting the gamma and effective 18%-IRE rating for film? You likened it to changing to a higher/lower contrast stock. How would you say gain factors into this?

Is it typical on a the newer D20/Genesis or F900/Varicam shoots to be constantly changing the scene files for different types of lighting? I have seen it done but I am wondering in a more broader sense. I guess you could have different settings like different stocks (daylight versus, tungsten) but for some reason I feel like having one master setting would be the best.
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#7 Walter Graff

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Posted 10 April 2007 - 09:39 PM

It's all about getting a good, solid green


Very simply green screen is about hue, PERIOD! If you took the time to use a true green screen paint or material, then you have a material that is designed to reflect 550 nanometers. It's not really pure green (556 is pure green) but ever so slightly yellow, the idea being it doesn't need a lot of light to saturate properly so the slight yellow pigment allows it to act more like an iridescent color and hence is easier to light to our eyes. Look at it this way. See the material in your hands or on the wall? The idea is to simply make it glow, so it is represented as close to the color it is without too much light which will wash the color towards yellow or too little which will make it darker. So regardless of how you light your talent, you should always light a green screen first for proper hue and even exposure, then turn off the lights and light your talent for the back plate. Then turn it all on and go.

The idea of under and over exposure for green screen vs talent is more a misconception based on a few things. First people refer to green reflection on the talent. Green reflection is a condition of both angle (camera/talent/Screen relationship and incident reflection) and the distance of talent to screen. For along time many people incorrectly lit green screens for illumination rather than hue. This meant they usually lit them too brightly because many arbitrarily lit the screen and added light rather than subtract it to get an even read rather than looking at trying to create a screen lit on proper hue and that "glow" made the color spill on talent let alone that they usually added light rather than subtracted it to make for an even screen so in the end they lit the screen more often too bright . And after a while the notion was that you have to be very careful with spill from a screen on your talent. "Common knowledge" was that you had to separate your talent as much as possible as a result. Nice but not necessary when you light a screen for hue. I demonstrate this in my DVD on green screen showing what happens in the post production side by demonstrating various things such as types of shadows, etc. Or if you want an easier example showing that a screen can be properly lit without spilling? Your evening weather man is about 6 to 12 inches from his green screen. Of course the Newsmatte that cuts him has a green suppressor that allows adjustment on his skin/cloths/etc, but so do you in post.

If you lit a screen for proper exposure you'd probably find something about 80 units of light on the screen but then again that also depends on your camera and how it is shaded and what f-stop gives you a good exposure. It might need 120 units. If the peds are off and gammas set certain ways on your camera you'll get different representations of green depending on how much light you use. But generally 80-100 units of light is more than enough to light a green screen in most situations.

So how much does all that translate to in IRE? Well factors such as lens and camera shading can affect the final outcome but generally 55-65 units is sufficient. There is no exact number. What should be more important is the saturation of color. Using a vectorscope you can better target your green saturation to correct green hue. When you use the vectorscope you can simply light the screen and see if your vectorscope target is in line with the green box and between the second outermost circle and the third outer most circle, a bit closer to the second outermost ring (75%). It doesn?t have to be perfect. It could also be in the center of the box as that would represent pure green. (Of course you need the screen to be lit as even as possible and this does not tell you that). If you've done this as I just described, take a look at the waveform and you'll know what is the 'correct' level of IRE is for your camera and the particular set up. Now look at your green screen. Does it look like the color it was before you lit it with a slight glow but not washed out? On a properly shaded monitor, does it look close to your eye? Then your in good shape. If it's way off then adjust levels. It shouldn't be if you follow what I said.

Ok, so what if my green is off (based on the vectorscope)? Here's the twist; who cares? We use green because it is well within the range of how well a camera sees in the CIE chromaticity and green covers a lot of that chart. We could use red for keying and do for certain situations but for human faces it is not a good idea. Blue is the color closest to the edge of the CIE so the one that can cause the most problems (our cameras imitate how we see colors and there ain't much blue to work with). And that twist I just mentioned? You can basically use any color you want for chroma key and video as long as what your talent wears doesn't interfere. The reason is because the devices/software that does the keying in post allows you to sample whatever color you want to as the color to cut. So, if your green is not perfect, that's okay as long as it is relatively even overall and especially where your talent stands/sits/etc.

Okay, so say you have that scope and light your green so that your green point is in the range I mentioned on your scope, what about the talent? Well your not going to light your talent twice as bright, or twice as dark are you? You could. See it doesn't matter. It doesn't matter because it's the green that is important to chromakey, not your talent. So if your talent is supposed to be standing in a tunnel in the final shot and is being lit by a small bulb hanging to one side of the tunnel, your talent might be only 40 units on the bright side and 10 on the dark. Who cares, he will cut because what is being cut is anything green, hence why I say in my articles, DVDs and lectures on proper green screen technique that the only thing that is important is the color of the screen and the evenness of it.

And if you are lighting your talent rather evenly (even keys) then you'll naturally see your talents exposure be slightly brighter to even with the screen. Remember that your screen ends up in the 55-65 IRE range and your talents face is going to end up somewhere just below 80ire in the even key scenario (probably closer to 70 IRE) hence why naturally your talent should end up around the same exposure as your screen. But if it's above or below then your still okay, it's not about perfection, but rather starts with proper representation of the green color. It all falls into place if you start with that.

How even is even on your screen from one spot to another? First off, here's a problem, your eye has the most receptors for green followed by red and then in a ratio of about 20:1/18:1 less is blue, hence why you can't read the solidly blue illuminated signs in strip malls at night clearly (they look out of focus). You don't have enough blue receptors to focus it well enough because as animals we never need to see blue clearly because food is not blue. So what does mean? Very simply, it only takes a little bit of green before your eyes are overloaded and you can't tell how bright and if one part is brighter than the other. So what can you do?

Some folks learn to see subtle differences by using a gaffers glass.

You could use a spot meter too. But that takes the same practice as zebras do.


Zebras? you can use them but they are sensitive by one IRE so if you think you are going to get a screen lit so perfectly as to have the zebras glow perfectly when you open the iris, you'll spend the rest of your life trying light that screen easily. At most you can light any portion of a screen to a tolerance of about 10-15% and that means that a zebra is more a good final check than a standard for lighting a screen easily. It's good but not easy with zebras unless you've done a lot of lighting using it. I say if you have your screen relatively evenly, you'll usually see a blob of a glow with the zebras as you open the iris going from the center of the screen towards the edges as you iris up.

Using a light meter, about 10-20 FC differences as you move it around your screen is plenty close for evenly lighting a screen and a well cut key in post.

Post? Probably about 70% of the knowledge comes from post. What do I mean? I mean if you never saw how a key is cut in post and what considerations and what factors make keys more difficulty or easy to cut, then you are missing about 70% of what you need to know as a cinematographer to properly light a chroma key screen for video. So learn it, and you'll find folks claiming your an expert person in keying. Your not, you've only hedge your bet by learning the most important part of the equation. It doesn't take much. What you want to see is how hue, saturation and luminance factors in adjustment translate to how much you need to light a screen and how what you light translates to a finished product.

Basically you want to see how what you've lit in the studio translates and what has to be done with the keyer controls in post to cut and then clean up your key so you have a nice relationship of the back plate to talent.

In the film world faster stocks often key worse than slower stocks as they often have more grain and that means your blue and green layers are affected.

Hope this helps. I condensed a lot into a small post so sorry if I confused anyone.

After literally hundreds of key shoots and many hundreds of hours in post with keying, there is a lot I've learned and sometimes I'm lazy extrapolating.



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#8 Matt Workman

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Posted 10 April 2007 - 10:12 PM

Hope this helps. I condensed a lot into a small post so sorry if I confused anyone.


Small? :blink:

Thanks Walter for the post, again hopefully I'm not the only one getting something from this.

To try to summerize your post even further:
- even lighting (10-20 footcandle tolerance)
- vector scope (check green hue is correct)
- green screen 55-65 IRE (depends on gamma, lens, shading, etc.)
- by eye should have and even glow similiar luminence to key light (obviously subjective and relative to shoot)

I have very little experience with the vectorscope, I usually use the RGB parade when I color correct or chroma-key. I've used Shake/Fusion/AfterEffects (primatte, keylight, etc.) for keying so I've done the software end. However like you said not everyone has done the post side. I'd like to have something concrete I can tell my gaffer so he doesn't kill me when we are lighting the green screen.

I have pulled keys from horrendous DV wrinkly muslin work light lit shots and they have worked surprisingly well, no Saline Project. But from a practical DP/Gaffer perspective thinking in terms of IRE and exposure makes sense. If I was talking with the VFX supervisor or an on set compositor we'd be talking different priorities. What do you usually tell the gaffer when he asks how we are lighting the background? (thats isn't supposed to sound condescending, I'm actually curious and I might steal it also, :P )

Your advice sounds credible having experience from production and post. So I have another question.

40'x40'x18' two wall cyc. Basic even lighting.

- 3x 6k Spacelites with skirts
- 10x cyc strip lites
- 2k's with diffusion

These are my initial thoughts of lighting ranking from favorite to "if we have to." I've seen simliar sized cyc's lit with all of these approaches, which one would you recommend.

Thanks Walter.

Cheers,

Matt :ph34r:
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#9 Brian Dzyak

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Posted 10 April 2007 - 10:20 PM

Very simply green screen is about hue, PERIOD! ...



Very nice, Walter. :)

I feel the need to clarify my own suggestion by saying that I never actually use the zebras to confirm or deny an evenly lit greenscreen. If the space and frame are small enough, I pull out my old Spectra incident meter and run it across the green to see where and when the needle moves. I'm not so concerned about "brightness" at that point, but about the illumination being even. After I'm happy with that and using my target stop as a guide, I'll knock the Kinos down as needed then work on the foreground.

If I can't get an incident reading across the green for one reason or another, spotting it from camera is the second choice. Point being, the zebra pattern in the viewfinder itself is subject to inconsistency caused presumably by the lens. I may have a perfectly lit greenscreen, but the zebras generally show that my edges are "hot" before the top and middle of the frame. Zebras are a terrible way to judge, in my opinion. But when the scopes aren't available or if someone doesn't have a meter, then I guess you use what you have. Not the recommended way to work, but when does any shoot really go the way it "should"?

:)
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#10 Walter Graff

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Posted 10 April 2007 - 10:47 PM

"- even lighting (10-20 footcandle tolerance)"

Basically 10 foot-candles is more than enough for any keyer to easily handle.

"- vector scope (check green hue is correct)"

Correct is relative as I said. If you are suing green, then use your scope ot make sure its a good hue of green. You can color pick in post.

"- green screen 55-65 IRE (depends on gamma, lens, shading, etc.)"

No, I said those factors are factors. But if your screen is in the 50-60IrE range then your okay for the most part.

"- by eye should have and even glow similar luminance to key light (obviously subjective and relative to shoot)"

Basically if you light your screen well then your talents exposure (if you are lighting him flat and not for a specific special background will be a little brighter. But he could be 20 IRE, it doesn't affect the key.


"What do you usually tell the gaffer when he asks how we are lighting the background?"

Get out of my way and let me do this!!! :) No actually I simply look at the final product and make sure it's to my liking knowing what I am doing in post. The guys I work with have a good understanding of what to do so I usually fine tweak if necessary.




Very nice, Walter. :)

I feel the need to clarify my own suggestion by saying that I never actually use the zebras to confirm or deny an evenly lit greenscreen. If the space and frame are small enough, I pull out my old Spectra incident meter and run it across the green to see where and when the needle moves. I'm not so concerned about "brightness" at that point, but about the illumination being even. After I'm happy with that and using my target stop as a guide, I'll knock the Kinos down as needed then work on the foreground.

If I can't get an incident reading across the green for one reason or another, spotting it from camera is the second choice. Point being, the zebra pattern in the viewfinder itself is subject to inconsistency caused presumably by the lens. I may have a perfectly lit greenscreen, but the zebras generally show that my edges are "hot" before the top and middle of the frame. Zebras are a terrible way to judge, in my opinion. But when the scopes aren't available or if someone doesn't have a meter, then I guess you use what you have. Not the recommended way to work, but when does any shoot really go the way it "should"?

:)


Very simply, unless you have lots of expereince with using zebras to gauge illum of your screen I wouldn't suggest you take it to heart. It can confuse more than help.
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#11 Michael Nash

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Posted 10 April 2007 - 11:46 PM

I am inexperienced with using the Varicam/Cinealta paint options and would only dare use them if we had an DIT on set. Should I be more bold with experimenting or does the "neutral negative for post" mentality make sense?

What is the film equivalent of shifting the gamma and effective 18%-IRE rating for film? You likened it to changing to a higher/lower contrast stock. How would you say gain factors into this?

Is it typical on a the newer D20/Genesis or F900/Varicam shoots to be constantly changing the scene files for different types of lighting? I have seen it done but I am wondering in a more broader sense. I guess you could have different settings like different stocks (daylight versus, tungsten) but for some reason I feel like having one master setting would be the best.


There is no real film equivalent to shifting the gamma in video (no simple process that does just that). The whole gray card concept is designed around creating a "normal density" at midtone for film as a standard of reference, but video doesn't work that way. In video, midtone-to-highlight reproduction is usually a more important reference (hence 70, 80, and 100 IRE zebras). All that gamma control really does is change the brightness of midtones relative to the highlights and shadows (try any basic image editor like Photoshop, Preview, Graphic Convertor, etc. and you can see what raising and lowering the gamma does). When you raise the gamma you're compressing or flattening out the tonal reproduction between midtones and highlights.

I likened raising the gamma and the black stretch (in conjunction with lowered exposure) to using a lower-contrast film stock because of the way it shapes the highlight and shadow response to a flatter curve. Also to distinguish the fact that it doesn't extend the dynamic range the camera is already capturing, it just reshapes the levels into a straighter line (video cameras generally have a bit of extra information near the bottom or "toe" compared to film, so you're borrowing some of this when you underxpose and boost the black stretch).

Of course pushing the knee or gamma too far can give you odd color shifts. The trick is to work within the known limits of the system, just like push-processing film. Besides, I'm not talking about altering the knee, just the gamma to help flatten out the transition into the point where the knee begins (oddly enough, Sony cameras seem much more susceptible to these greenish color artifacts than Panasonic cameras). And of course a higher gamma gives you less saturated looking color; lower gamma appears to saturate more.

You just have to try these things out and see how they work for you. I don't usually push the Gamma in Sony's to more than +30. No matter what a DIT or lab technician tells you, you never know until you try it yourself.

Gain is just electronic amplification of the signal, where amplitude=luminance. The closest film equivalent is push processing, although the results to the image aren't quite the same. +6db of gain is similar to a one-stop push in terms of exposure. Pushing film tends to increase contrast and color saturation, whereas video gain usually only adds noise but keeps the contrast and color otherwise the same (up to a point, at least).

I can't speak for everyone, but with the Cinealta, Varicam, and SD broadcast cameras it's not uncommon to tailor the gamma, knee, and black stretch to the lighting setups (and dynamic range, with the Varicam). Think of it like electronically changing film stocks or filters -- aside from speed you might choose something with a little more "snap" on an overcast day, or use an ultracon filter on day exteriors. It's just another form of control that the DP has over the information getting captured. There's no inherently "right" or "better" approach any more than there is with film. Some people don't mess with it; some people use one film stock for everything...

I have very little experience with the Genesis, but I understand it's designed to be used without in-camera tweaks and instead manipulated in post. However, the image recorded in camera is viewable as-is, unlike the Viper in filmstream mode, which produces a very flat, green, "neutral negative" that won't look right until you correct it in post. I don't know that much about the D20.

I mention the gamma in the first place because many users of the F-900 lower the gamma a bit because they feel it gives a more "film like" look, and when you get the camera from the rental house or owner it may already be set up that way -- and your gray card reproduction relative to "proper" exposure depends on that. Bear in mind that there is no "neutral negative" on the F-900; when you get the camera it's a negative that's been designed by someone, even if all parameters are at default. You have to decide if that look works for you as-is, or if you want to tweak it and how far.
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#12 Matt Workman

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Posted 11 April 2007 - 12:11 AM

Get out of my way and let me do this!!! :)


Officially stolen, that is my new motto. :lol:

Michael Nash The insight on the gamma is very helpful. I am very familiar with photoshop curves, levels, etc. but still applying it to the F900 confuses me, less now. I try to read the Goodman's Guide to the Varicam and memorize the important paint settings but I'm still rusty. I would like to have that stuff mastered so I can talk confidently to a DIT when that day comes.

It seems that gamma/knee/toe etc. are the new form of push processing and lab "knowledge" that you referred to. I am now going to definitely make my own scene files based on a "hopefully" properly calibrated HD monitor before this shoot, time willing.

While I'm not going to claim control over the final LUT (well its not in logspace) I do hope to gain some F900 paint skills from this next shoot. I wish I could manipulate the gamma curve with a mouse instead of the menu's, ehhhh.

In a related note I read that Claudio Miranda on his Viper shoot with Fincher takes home cineon still frames and color grades them in photoshop to send to Fincher. Basically creating his own LUT for the colorist to reference.

http://www.studiodai...issue/7847.html

There is something pure about shooting Genesis uncompressed. It could be construed that you lose control to come degree but you are also only worried about lighting/framing and less about gamma/gain/shading etc. Its making a colorist nessecary and seperating roles that were once combined. Not that the colorist hasn't always been important but now its almost completely out of the DP's hands. (Obviously I've never shot with the Genesis but this is just a thought)

Just trying to get up to speed for this next one, thanks for the help guys.

Cheers,

Matt :ph34r:
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#13 Michael Nash

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Posted 11 April 2007 - 12:27 AM

While I'm not going to claim control over the final LUT (well its not in logspace) I do hope to gain some F900 paint skills from this next shoot. I wish I could manipulate the gamma curve with a mouse instead of the menu's, ehhhh.


You can ;)
http://www.cinematog...lderForF900.htm

You might get some useful info from this as well:
http://www.jkor.com/.../F900paint.html

It is great to read up on this stuff, but ultimately you still have to try it. Acedemic education gives you a fighting chance, but you still have to wrestle with the real-world variables. I spent about 3 hours playing with a Varicam and a Cooke S4/Pro 35 setup the other day just to learn the nuances.

Apparently the Viper/LUT approach is not without its compromises, since Michael Mann et. al. went with "video stream" for Collateral and Miami Vice in order to monitor the image without on-set LUT's and the signal delays they apparently impose. Maybe the LUT/monitoring situation has gotten better since Collateral, since Fincher and Savides reportedly used that on Zodiac. But I have yet to use the Viper -- it's the f^(*!#@ post costs that kill it for small-budget projects!
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#14 Matt Workman

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Posted 11 April 2007 - 12:40 AM

To quote Mr. Mullen from that link.

"The truth is that I think the 8-bit recording is the ignored elephant in the room, the major factor that determines image quality while people futz with fairly insignificant adjustments to their gamma, knee, etc. settings."

LOL, Futz :lol: However I will say that good color correction, in camera or in post can save 8-bit HD footage. SAVE IT!

With that being said, where do I download this magical "User Gamma Builder System?" Maybe I can check out a paint box, those are a little easier than the menus.

Viper 10-bit uncompressed log. Yeah thats nice. You are right, you need a 2k Lustre or a full on DI suite to even play that stuff back real time with a LUT. Even HDCAM-SR was too much for this shoot.

Film is easier, sheesh.

Cheers,

Matt :ph34r: :ph34r:

PS: Is the Viper 2/3" ?! C. Miranda said they shot with Digi-Primes.

Edited by Matt Workman, 11 April 2007 - 12:43 AM.

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#15 Michael Nash

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Posted 11 April 2007 - 01:14 AM

To quote Mr. Mullen from that link.

"The truth is that I think the 8-bit recording is the ignored elephant in the room, the major factor that determines image quality while people futz with fairly insignificant adjustments to their gamma, knee, etc. settings."

LOL, Futz :lol: However I will say that good color correction, in camera or in post can save 8-bit HD footage. SAVE IT!

PS: Is the Viper 2/3" ?! C. Miranda said they shot with Digi-Primes.


David was referring to extending the latitude or dynamic range of a camera through tweaks, as was I. He's absolutely right that it's just different ways of slicing up the pie -- you just have to decide for yourself what's the best approach to getting it in the "can." The F900 has 10-bit pre-compression DSP but 8-bit recording, which means that in-camera tweaks tend to hold up slightly better than post. As I said in a recent post about day-for-night with the HVX, it's generally best to do in-camera what you can do well in camera.

Yes, the Digi Primes are B4 mount for 2/3" inch cameras. The Viper is just that, along with the F900 and Varicam (and every broadcast SD camera out there, which means you can take advantage of the DigiPrimes on an SDX-900). The Genesis and D-20 use super35-sized sensors, with PV and PL mounts, respectively.
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#16 Michael Nash

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Posted 11 April 2007 - 02:53 AM

I meant to include that I think the crux of this discussion is knowing where to draw the line between what's best to do in-camera vs. post. Ultimately that comes down to a personal choice based on both education and experience, just as it does for film. And it's an ongoing process; after 18 years I'm still refining it!
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#17 Walter Graff

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Posted 11 April 2007 - 07:44 AM

Ultimately that comes down to a personal choice based on both education and experience, just as it does for film.



This is probably number two on the list of how-to's. The only rules are what works best for you. There often are no hardcore absolute numbers in life, just guidelines that fall into a range. I've found over the years that my tastes and manners of doing things move through the range as I learn more and find ways that work best for me. Hence, to say there is any one definitive number on a scope for a green screen illumination would be inaccurate. There is a range. That range is based on the camera, the setting, and taste. Bottom line, it's about color. If you find a color you like and light it evenly, then you've done what you need to do. Beyond that, it's about experience and it's experience that lets you see the range rather than the number.

Edited by WALTER GRAFF, 11 April 2007 - 07:45 AM.

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#18 Matt Workman

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Posted 11 April 2007 - 10:57 AM

That makes sense if the F900 makes the adjustments in a 10bit space then downconverts to HDCAM. So it is slightly better to make adjustments in camera, goes without saying testing is needed. But the theory makes sense.

The F900R and F950 are 12bit before they go to tape right?

For some reason I put the viper up there with the D20/Genesis super35mm CMOS sized sensors. The Viper is more like the new Sony F23 then, right? I'm interested in comparing the mechanical shutter on the D20 to the electronic ones.

I wonder how much Bill Pope does for the Matrix, etc. for lighting the green screen. I would assume the VFX supervisor or a special plate DP handles that while he does the foreground. No clue, just speculating. Or the rigging gaffer probably understands what is needed also.

I can understand and appreciate that there are no rules...but even if they are wrong or tempramental I like to have something in mind before I go on set, even if I throw it away. You guys have a lot more experience to pull from, I'm still going to use the 50IRE as a crutch to start off.

Better believe I'll post set photos and the final video, hopefully a HD h264 so we can see how the keying came out.

Cheers,

Matt :ph34r:
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#19 David Mullen ASC

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Posted 11 April 2007 - 11:10 AM

The Viper and the F23 are both 3-CCD prism-block 2/3" sensor cameras. Otherwise the F23 looks like the Genesis due to the onboard HDCAM-SR VTR.
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