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Lowlight/underexposure with RED (9 replies and 5 comments)

a.kozel
10 months ago
a.kozel 10 months ago

Hi, 

I've been having trouble working with the RED sensor (Dragon & Helium) in lowlight. I've tried a few times shooting in blue hour or creating small pools of light in a scene and letting parts of the space fall into the blacks. However, when I bring the footage into post, the shadows often seem excessively noisy in a bad way. 

I recently shot a scene in blue hour and was still decently exposed (skintones in the IRE20/30 area) which is still under but the image just seemed mushy and noisy. 

Thinking of the rooftop scene in Sicario that was all natural light and Alexa, the image seemed to still have some definition and natural noise that felt like film grain. I've also AC'd for DP's shooting the Alexa around 1600 in blue hour and still get a nice image. Grainy but colors and tones are pleasing, and that was viewing the footage straight out of camera on DIT computer.

Is this an issue on RED sensors or is there something I need to be doing either in camera or in post? I've seen some amazing images come out of RED cameras but I almost feel like I have to overexpose to get light into the shadows then bring everything 1-2 stops down in post to avoid mushy images. 

dmullenasc
10 months ago
dmullenasc 10 months ago

You should submit this question to the RedUser forum -- maybe you are converting the footage incorrectly from raw.  Though usually the problem is just too much underexposure or you are brightening the image too much in post.

I haven't shot with a Red camera in a while but here is a frame from a twilight scene I shot in 2011 on one of the first Epics with the old Mysterium-X sensor.  I don't recall the exposure in terms of how much I let the twilight get underexposed -- I think I set the camera to 1000 ASA and set the lens to an f/2.0 and waited until it got dark enough.  But it definitely was underexposed for the effect I wanted, I didn't darken the background view in post.

https://www.rogerdeakins.com/wp-content/uploads/2016/08/bigsur_dusk.jpg
dmullenasc
10 months ago
dmullenasc 10 months ago

Here's another dusk shot that I did on the old Epic -- I think I had the compression rate up on this one because it was shot at 96 fps, and the focus is a little off (the bottle under his arm is sharper than his face.)

https://www.rogerdeakins.com/wp-content/uploads/2016/08/bigsur_dusk2.jpg
dmullenasc
10 months ago

Of course, this is also a compressed jpeg posted online...

dmullenasc
10 months ago
dmullenasc 10 months ago

One issue with Red cameras to watch out for is the black calibration / black shading, you have to make sure that's been done properly.

 

a.kozel
10 months ago

David, thanks for your response! I think black shading and temperature have been the main culprits. I try to black shade before each gig since I always rent but unfortunatly most the time I don't have time midshoot to reshade.

I shot with the Helium on a short and it was extremely hot in the hotel we were shooting in, the camera temp soared, and there was terrible noise in the shadows in the footage since I was shooting a very lowkey moody scene.

Stuart Brereton
10 months ago
Stuart Brereton 10 months ago

This is a problem that I've had with RED cameras ever since the RED One. Shadows seem to block up and become noisy much quicker than other camera systems. I freely admit it could be user error, but as I prefer to shoot with other cameras anyway, I've never really taken the time to get to the bottom of it.

standucci
10 months ago
standucci 10 months ago

Dragon sensor has been updated to correct reported issues and until Helium sensor gets figured out the Dragon sensor is apparently better. It still doesn't have good underexposure latitude especially in comparison to ARRI, Sony. 

We did some underexposure testing a while ago with Scarlet W, both their 'normal' and low light OLPF, I'll include a few below. First 2 are OLPF, Last 4 are 'normal' OLPF. Definitely a difference in grain structure and under exposure latitude between LL OLPF & 'normal' OLPF (noticeable color shift as well although uncertain if due to IRND's).

Which optical filter did you use? Which version of Redcine X? Apparently the stupidly named "IPP2" image pipeline has better shadow detail and better noise reduction. 

https://www.rogerdeakins.com/wp-content/uploads/2016/08/800_-4_Corrected.0000000.jpeg
https://www.rogerdeakins.com/wp-content/uploads/2016/08/800_-4_AS.0000000.jpeg
https://www.rogerdeakins.com/wp-content/uploads/2016/08/800_-2_Corrected.0000000.jpeg
https://www.rogerdeakins.com/wp-content/uploads/2016/08/800_-2_AS.0000000.jpeg
https://www.rogerdeakins.com/wp-content/uploads/2016/08/640_-4_Corrected.0000000.jpeg
https://www.rogerdeakins.com/wp-content/uploads/2016/08/640_-4_AS.0000000.jpeg
a.kozel
10 months ago

I use DaVinci to grade but that has been tricky with the new IPP2 system. My version has the Widegamut curve and log3g10 but all my LUTS are based on older RED gamma/color settings. The widegammut and log3g10 combo leaves the footage feeling pretty desaturated and I have a harder time getting color back into the shoot in grading.

tom hines57
10 months ago
tom hines57 10 months ago

There is a symbol labelled T/E displayed on the monitor... I believe stands for Temperature and Exposure. When the sensor Temperature, or ISO and frame rates change... either the T or E will turn Orange and then red. If either the T or E or both turn Red you need to re Cal Map or you have terrible noise. 

Miguel Angel
10 months ago
Miguel Angel 10 months ago

There is definitely an issue with black shading and noise if you don't calibrate the camera properly plus you have to keep an eye on the Temperature 

I shot this just with natural / available light and the Red Dragon a couple of years ago. 

https://vimeo.com/203587956»

There is no noise reduction at all and some of the images were shot with a very low level of light, like just a match 😀

I recall shooting it with either the Skin Tone or the Standard OLPF. 

https://vimeo.com/212376682»

The above one was shot again with available light but it was the Lowlight OLPF which I prefer when shooting with the Epic Dragon. No grading.

 

Hope it helps. 

Miguel Angel

a.kozel
10 months ago

Thanks Miguel, your first link is a great example of what I was aiming for but the image just completely fell apart. It just seemed muddy and lacking color depth. I think the biggest issue was not black shading before the shoot. Wish it wasn't such an issue with RED. With Alexa it seems like I can shoot it no matter the condition and the footage is always good.

Miguel Angel
10 months ago

You're more than welcome.

Another thing to take into consideration is the compression.

If I have to shoot on a Red (which I don't do anymore because I prefer the Alexa) I use the best compression available, which I think that is 2:1 or something like that.

Have a lovely day!

K.Wasley
10 months ago
K.Wasley 10 months ago

i think the elephant in the room here, and what has the most dramatic impact on noise with the RED is what ISO you are rating the camera. I shot a feature a while back on RED dragon, rating it at 320 - 500 ISO with most of it at 320. If you do this you will get very nice clean blacks with plenty of room to lift the shadows. I think RED's sensor rating is very optimistic. So I would recommend rating the camera at a lower ISO in your light meter or in camera.

Shaka Agina
10 months ago
Shaka Agina 10 months ago

One Important thing I found out was to Black Shade after letting the camera run for a while. Now I would find out, if possible, what fan speeds would be acceptable to the Sound guy and let the camera run for 3-5 minutes at that speed. This would get me the temperature that we would be shooting at for that particular location / scene etc. At that point I would then black shade. Providing me with some affirmation that the temp we're shooting at wont vary as much to affect the sensor to the point of terrible noise.

This forum post prompted me to cut a quick clip and write up of a test I did a while back regarding this issue, however the camera that was tested was the RED SCARLET MX. Which is notorious for such issues.

Here is the video in question: https://vimeo.com/248678516»

I'm still such a junior to all of this but its sticking slowly!

S.A

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