Shooting Night Exteriors above Noise Floor (5 replies and 3 comments)
When Shooting in low key situations during night exteriors, how do you keep the shadows above the noise floor of the camera? now that your switched to digital.
Do you Light everything a stop over and then bring them down in post or use any kind of post Denoise?
i've added screenshots from your prisoners movie where subjects are lit naturally through the incandescent bulb yet above the noise floor in the shadow regions.
Really looking forward for your reply sir.
i've added screenshots from your "Prisoners" movie where the subjects are lit naturally through the incandescent bulb yet above the noise floor in the shadow regions.
Kindly awaiting your reply Roger.
Dark scenes are not necessarily noisier than bright scenes. I mean, what if you had a bright, high-key interior scene and at some point, someone turns off the light and then turns them back on again? Or someone in a black coat walks by the lens and fills the frame for a moment? Or someone covers the lens with the lens cap for a moment? Does the noise increase suddenly just because the frame got filled with more dark areas or goes black? So if you like the noise level of the Alexa at 800 ISO, for example, why would it be then noisier at night than in the daytime if both are shot at 800 ISO?
If you find the base noise at a selected ISO to be acceptable, then the noise only increases if you take an underexposed area of the frame and try to lighten it in post. I suspect Roger is so consistent and accurate in his exposures and lighting that he isn't trying to lift up his shadows in post to fix something, so there is little risk of an increase in noise from the normal level that the camera gives him at his selected ISO.
Also keep in mind that the noise at the very last stop of shadow information when looking at a log gamma image is buried by the contrast and black level of a standard display gamma -- it would only become visible if you lifted the blacks in order to pull the detail to a brightness level that it could be seen while using this display gamma. I think one mistake some people make is viewing a log image on set and thinking that all the shadow detail they see will and should be visible in the final image seen with the correct gamma -- it's a bit like lighting for the contrast range of a film negative rather than the display range of a film print.
Another problem that affects people using consumer video cameras comes from not disabling auto gain, as soon as the exposure drops below a certain level, the camera starts boosting the signal to compensate.
So if the general noise level of the ISO setting you have chosen is acceptable to you when viewing the image with the correct display gamma, it shouldn't be a problem to then leave an area unlit anymore than it would be a problem for characters to wear black clothes or turn out the lights in the room during the scene. If there is a problem, it's either because you've chosen too high of an ISO rating or because you aren't viewing the image with the correct display gamma LUT applied, or you are lifting the blacks in color-correction to bring out shadow information. Otherwise, just moving the camera from a lit to an unlit area should cause a change in noise level.
"Otherwise, just moving the camera from a lit to an unlit area should cause a change in noise level." SHOULDN'T not should, sorry.
i agree with you on nailing the right exposure on set in the camera and not pushing the shadows much in post will keep the noise at a minimum but i wanted to know if the ETTR(exposing to the right) technique is applied while filming digitally and then bringing back them in post so the shadows drop down below the noise floor of the camera.
ETTR is a still photography technique. The problem with applying it to dramatic cinematography is that we don't photograph each scene in a single shot, we shoot multiple shots that build up a sequence, so using ETTR literally would create a lot of mismatched shots that would have to be fixed in post to match each other again. Imagine a shadowy room where one character is under a bright lamp and then other character is standing in the dim shadows, or the same character moves from the bright area to the dim area. ETTR would demand that the person in the shadow, in their coverage, be exposed as fully as the person under the bright light -- and then in post you'd have to darken that person back down to the intended level. And what if in the middle of the scene, the lights go out and the room is supposed to be very dark with just a hint of moonlight? ETTR would force you to open up the lens so that the moonlit room would be practically as bright as a daytime room. So in practice, ETTR doesn't have a lot of use in cinematography unless you are doing single-shot sequences or a montage, for example, but even then, it is more common to expose closer to the intended look.
The other problem with ETTR is what are people looking at on the set monitors? You'd have to have a DIT color-correct every shot live so that you and the director would see something close to how the shot was supposed to look like. Same goes for dailies, they'd have to be timed to match.
What is more common is just to keep in mind that to avoid noise, sensors like exposure, so you might take that into account in certain scenarios. For example, I've lit a room for a dark moonlit scene and the camera was set to 800 ISO using an Alexa, and the director wanted me to expose it even more darkly. Being worried that in post, he might change his mind and not want the scene to be that dim, and not wanting to then have to work with a very underexposed image, I darkened the image (and the log recording in ProRes) by switching to a lower ISO rather than closing down the lens iris, so basically darkening it for the recording by pulling down the signal rather than robbing the sensor of more light. So let's say I darkened the image by 2/3-stop by switching from 800 to 500 ISO -- if they decided to brighten it again in post by 2/3-stop, it would have been as if I had shot it at 800 ISO after all in terms of noise.
Thank you David Mullen. That was a very good answer to things I been wondering about for the last 10 years or so.