Jump to content


Photo

Exposure on Viper Filmstream (Raw)


  • Please log in to reply
2 replies to this topic

#1 renfield sonia

renfield sonia
  • Basic Members
  • PipPip
  • 32 posts
  • Digital Image Technician

Posted 09 February 2011 - 06:07 AM

Hi, I'm working as a HD Technitian in a HD feature film in wich we're using a couple of viper filmstream cameras. As they feed a sort of Log curve the image is flat and greenish. We've been correcting the monitoring image by applying LUTs and would like to hear some opinions about exposure. Eventhough we know where our grey, black and white points are supposed to be (around 40, 10 and 70 IRE) the DP is using almost always the whole range the camera can take, which in some cases, reach the 109 IRE for specular highlights or 100 for bright whites (white backlights or white clothes). I'm used to check the raw footage by grabbing some frames using a cinetal monitor or checking out the footage, just to see if we've clipped any light. By adjusting the frames with photoshop I can see roughtly how the colour correction will apply to the image and because of that I'm confident about using the whole sensor range because it's easy to control highlights and so.
I was trained to try to expose images technically, using the waveform as a basic tool, but shot my last jobs with some DPs that like to expose the way they want the image to be at final point, rejecting the safety room I would recomend as a technitian)
My concern is about the final broadcast image: I know that the DP us exposing like we would do with a negative stock, but I'm not quite sure about how this increased latitude will output in TV, basically I'm concerned about the possibility of loosing too much detail in highlights (we're exposing until 109 IRE)
Would like to know opinions about if it would be better to expose using the Input-output levels recommendations (setting the grey point at 40IRE and the skin tones at 50-60IRE, which would feed an underexposed looking image) or if to expose by eye and then trusting colour correction...
I know this post can seem a little basic but I've heard so many opinions about that that I'm not sure about the best reasons to use one or another method.
  • 0

#2 Phil Rhodes

Phil Rhodes
  • Sustaining Members
  • 11938 posts
  • Other

Posted 09 February 2011 - 06:31 AM

Since it will inevitably get graded between where you are and broadcast (or filmout, or whatever) I wouldn't worry too much about the super-whites. They can be fixed later, or at least they can if your grading facility is properly set up to handle it - might be worth asking the question. I'd be more worried that by doing that you're probably coming quite close to clipping things off entirely, but that's something only you can judge, having access to the actual pictures.


The usual approach is to generally watch a monitor with a LUT in it - if you have Cinetal, you're in a great position. Personally I quite like to have a LUT that makes things look just slightly more clippy than they really are, just by a couple of per cent, so that when you see it just start to clip on the monitor, you have some hope that you still have it on the actual recording. Nobody should be routinely looking at the unprocessed log image and trying to light to that.

How are you recording it?

P
  • 0

#3 renfield sonia

renfield sonia
  • Basic Members
  • PipPip
  • 32 posts
  • Digital Image Technician

Posted 09 February 2011 - 09:55 AM

We're using a P2 recorder (10 bit 422) for the hd stream of the viper. I used to work with a Stwo OB1 with bigger budgets where you could apply a LUT on itself and preview the image with an onboard monitor (astro in that case) with the LUT. Now the operator has to work with uncorrected image, but, as the viewfinder is black and white and most of the footage will be processed to be black and white the issue is not that big. The LUTs were made with the intention you talked about, boosting the whites to clip before the sensor does (increassing the contrast and color correcting the green cast of the viper), but not too much so to avoid the DP to underexpose too much. Now he's exposing by eye and we use to have some white almost clipped points in the image (if there are practical lights the chance for them to be out of the range are important, as the DP's using them as light sources aswell).
What would you do with grey points and skin tones (the luts are made to respect the average mid tones, but if the faces are underexposed, or there's big contrast on the scene, sometimes it's difficult to judge if not by eye... I just trust the DP and call his attention if I see the whites above 100IRE)
I'm also using an early version of IRIDAS SPEEDGRADE to create LUTs for the CINETAL, do you know any other application (my version doen't have a waveform monitor).
I'm also concerned about green channel overexposure, as I'm judging a YCbCr 422 signal with the astro monitor, I don't know where my 3 channels are one in relationship to another, just guess that luminance channel still the green one and guessing that this channel will be the first one to clip...
  • 0


Broadcast Solutions Inc

Willys Widgets

Wooden Camera

FJS International, LLC

Aerial Filmworks

Opal

Gamma Ray Digital Inc

Abel Cine

rebotnix Technologies

Ritter Battery

CineLab

Media Blackout - Custom Cables and AKS

Visual Products

Rig Wheels Passport

Technodolly

Glidecam

The Slider

Paralinx LLC

Metropolis Post

CineTape

Tai Audio

Wooden Camera

CineTape

The Slider

Aerial Filmworks

Broadcast Solutions Inc

Ritter Battery

Media Blackout - Custom Cables and AKS

Gamma Ray Digital Inc

rebotnix Technologies

CineLab

Tai Audio

Visual Products

Willys Widgets

Paralinx LLC

Metropolis Post

Glidecam

Rig Wheels Passport

Abel Cine

Opal

Technodolly

FJS International, LLC