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Helium horizontal sensor bars in footage

Joe Karably

Joe Karably

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Hi all, recently purchased a Helium from a reputable guy. The camera went through RED for processing and received clearance w/flying colors.
I filmed for the first time with it last night for some test shots for an upcoming short and got really noticeable horizontal noise patterning going across the back of our subject's head and hat.
I've never seen anything like this before on a Red. Can anyone tell me if they've experienced this before? Is it the lighting the venue was using? The camera was blackshaded prior to filming.

Edit: Link to 2 shots. https://vimeo.com/748367153
 

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Okay, the first shot walking outside, I can't tell if there's anything wrong other than maybe compression artifacts or noise. There may be something in the raw video but I'm seeing a compressed online video version so it may not be as visible on my screen.

Second shot, I would most definitely blame the CFL bulb lighting, there's rows of them in the stables and they are clearly making a matching pattern that seems to adjust right along when he moves. Did you have a hood or mattebox or was it just the bare lens? Wide open? Closed down?

Did you use any compression or were you at max quality? Lastly, did you try some denoising to see if the artifacts went away or were cut down to not be as noticeable? I've heard Helium footage can be noisy but the 8K resolution gives a lot of forgiving room for noise adjustments.
 
Looks like sensor smear. It happens in high contrast images when you get very bright areas right next to darker ones. The Helium sensor definitely shows it under those conditions. Other RED sensors have all but eliminated it.

In the first shot you can see the smear going to the left off the bright hat into the darkness. In the second you can see it coming from the bright lights on the left into the darkness behind his head.

I downloaded the clip to see more clearly what was happening, then applied a reasonably contrasty but normal grade and the sensor smear practically disappears as the highlights are pulled down and the shadows slightly darkened.







Worse examples have made it onto broadcast TV.
 
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Les, thanks so much. I also did a fairly moderate grade and it seemed to negate a lot of what was happening. I also feared a smear, and am assuming it's on the back end of the sensor as both the front and skin tone OLPF are 100% clean. Here's a DB link for anyone who wants to see it in 4K. Definitely makes me nervous having a camera react to lighting like that, these were definitely a step above your standard ugly sodium vapor bulbs.

https://www.dropbox.com/t/0FIovVWMTlbuLUgz
 
Sorry I wasn't more clear Joe, 'sensor smear' refers to the actual pixels on the sensor bleeding into each other. It's not an optical thing outside of the pixels of the sensor themselves causing strong light to 'smear' into adjacent pixels. There's nothing wrong with your camera, it's just that the Helium sensor packs so many tiny pixels together (smaller pixels than with any other RED sensor) that the 'sensor-smear' effect isn't always avoidable. It's just something that needs to be taken into consideration when shooting bright sources of light or high contrast content.
 
Damn. This is the first I've heard of this with regard to the Helium. And yeah, it was definitely surprising as I had never seen it on any of the Dragon sensors I've worked with since even the Raven.
 
In that link Phil Holland specifically states, "This example is of the Skin Tone - Highlight OLPF, which does indeed exhibit CMOS Smear easier than the other OLPFs due to its profile/calibration." Combine this with a very bright clipped/almost clipped next to a very dark area, light is going to bounce around. Also seems to be shooting at high ISO of 1600-3200 with Helium (and other sensors). Shooting at 800 ISO with standard OLPF I have not seen it in Helium, or if so it was so subtle that I never noticed.
 
I need to do another inventory and round of tests on this particular one, but I believe in the RED world DSMC2 Monstro, DSMC3 Komodo, and DSCM3 Raptor are the only cameras that don't exhibit CMOS Smear in this situations.

I'll double check on Venice 2, but Alexa 35 does exhibit the smear currently for some perspective on latest bodies.

It's another one of those mitigatable things in practice, but you do need some control over your exposure and lighting to do so.
 
Phil, would you mind if I DM or email you to discuss further?
 
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