About fill light.

[illia]

Hi Dave, I recently shot a documentary short film in Bolivia using a viper camera and 422 raw mode. We didn't have any budget for lights and we were really short on our crew... so we almost always shot using available light.
I tend to prefer backlit situations for the scene and we tried to use this as a formula, trying to avoid the amazing top light that hit our heads at 4000 m of altitude and close to the equator. Anyway, I found that I had to make almost always a compromised exposure. Let's say we had to shoot in an interior using the windows as main source of light. If I placed the characters in front of the window so to wrap a little bit the faces, but leaving the window on frame so to have some depth on the shot... I found on some cases that what seemed correct by the eye didn't turn out fine on the final image (viper anamorphic mode shows a great amount of noise on the dark areas of the image)...
The point is that if I had exposed for the dark area I would have had overexposed areas on the image (I mean cliped ones) which I don't like... but I don't really enjoy the resulted solution as big areas of the faces were too dark... Anyway, that's a minor problem as I found out the same problem in a different situation: on exteriors while shooting on shadow areas of the street I found out that the lack of contrast plus the dimmed light resulted on a poor image (I don't think overexposing would have been the solution, unless I was thinking on having more room in color correction to bring down the dark areas so creating more contrast)... I guess I'm talking about a contrast issue, as raw footage is so milky I found difficult for me to previsualize the scene (the dark areas seem overlit) but we didn't have any LUT displaying device... so... I liked the overall atmosphere of some images but wonder what would have been the correct amount of fill light to avoid noise but keeping the intention of the light... (the second question would be about those shadow situations... who to make them more appealing...)
Hope you understand my doubts...

 

[David Mullen ASC]

Log really isn't meant to be viewed on a monitor, it needs some sort of LUT or at least, a serious boost in contrast by playing with the dials on the monitor. Viewing Log means you are seeing the noise floor of the image when you really want to keep more shadow detail above that, which, yes, means sometimes using more fill light and/or overexposing a bit more in order to decrease noise in the shadows, and then crushing things down a little in post later. That's why it helps to judge the image on a monitor with some sort of gamma correction / contrast added to the Log image to bring it closer to Rec.709 gamma.

Though in a pinch, if the Log is not too flat (Panalog in the Genesis, for example, is not as low-contrast as Log-C in the Alexa), you can get away with viewing Log but crushing the blacks on your monitor and then also remembering to add a bit of fill to the shadows since in post you'll want to push down the blacks (now if you don't need shadow detail, just black blacks, then you don't need to add more fill.)

Available light photography at night can often get too low in contrast due to having a lot of underexposed dim ambience without any decent highlights. It helps to add some true blacks and whites into the frame, either by framing in a hot practical, adding a hot highlight, and some black shadows as well.

You could also try using a digital still camera shooting in JPEG mode as a way of seeing the scene with some gamma correction applied.

 

[illia]

Thanks a lot Dave,
What would you think it would be the lowest level in which you'd place a face, let's say you're in an interior and you want to keep the ambient dimmed... if 40IRE is medium grey, placing faces at this level would be underexposing the skin tone for about 1 stop... I've noticed that below 20 IRE the noise starts to be noticeable... so 30 IRE would start to be too dark for a face? I'm saying so because I had real troubles while shooting a feature film on alexa RAW... (I was the DIT) the lab came out with complains that many shots were being underexposed... and even if I was keeping the same philosophy than with other cameras, I could notice this noise around 20 IRE. The problem is that I don't know if the lab was handling RAW footage properly (heard that thay didn't have the proper plugins)... Anyway, besides skin tones they kept on complaining about big areas that were underexposed and showed noise... areas that weren't lit on the first place... so ment to be dark (that is for sure a DP issue so I don't decide were to put the lights...) but... about noise... what about those parts of the image that are below 20IRE and don't mean to be black but just dark, showing some color and texture detail... should we overexpose this areas? (let's say a dark background in a interior daylight room)

 

[David Mullen ASC]

I don't really think of exposure that technically -- if I'm shooting in a way to get good blacks and less noise by how I rate the camera and how I set-up the monitors, then I just expose faces for however dark in the frame I want them to go. I suppose if I didn't have a good monitor properly set-up, then I'd have to rely on a waveform or histogram reading.

You'd first have to know how the Log was designed for that camera, where black and white it (for example, on Panalog, black is something like 10 IRE and white is 70 IRE, but on the Alexa in Log-C, black is more like 15 IRE and white is more like 65 IRE, or maybe only 60 IRE.) This is based on a 11-step chip chart, basically five stripes under medium grey and five over. This is why on the Alexa, the 11-stops of stripes fall into such a narrow range in Log, because the camera can record 14-stops of DR.

I don't know where the Viper Log places black and white.

The noise problem from lifting underexposed areas up in post that were meant to stay dark, that's another problem altogether -- that's color-correcting an image in a manner it wasn't intended to be color-corrected for, on an image with enough general noise that you are limited in your flexibility to brighten things. At that point, if you really need to give a colorist more flexibility to brighten your footage, you either have to rate the camera slower and thus lose some headroom, or employ noise reduction processing in post and perhaps lose some sharpness. Either that or don't use such a noisy camera like the Viper or don't let colorists brighten your images if they weren't exposed that way. You can basically tell the producers that the image was exposed correctly for the look you wanted and that there isn't flexibility to change their minds in post because the Viper is a noisy camera.

You can always add more fill to shadows and then crush them down in post to add contrast, but there are limits to that technique before it starts to look artificial, that you are adding just adding a lot of contrast to flat lighting. But it doesn't hurt to do a little of this technique and give yourself more flexibility to color-correct the shadows. Same goes for overexposing or rating the camera slower -- yes, that will reduce the noise but also reduce the headroom, so there are limits to how far you want to go in pursuit of a lower noise image. But being a little more conservative with exposing doesn't hurt.