FS7: magenta cast in cineIE/slog3

K

kevin gallagher

Active member
On a shoot last week and I encountered what appears to be a somewhat common thing with the FS7. A magenta cast throughout the entire image but especially in the darker grays. Now, I have had this camera since it was first released and have never seen it do this before. In fact, I find it to skew towards the green a bit overall.

The scene was a room scene on a sound stage. Tungsten lighting all controlled nothing mixed. The set dressing and props were all black and white shades of gray, no color in the scene except talent. The darker grays all had a magenta cast that was pronounced enough that the client freaked out. At first I thought it was the LUT I was using but switching around to various other LUTS didn't help. After doing some research I found some guy who was selling a "magenta killer" LUT for the FS7 and other Sony cinema cameras but it did nothing to help the overall cast. We ended up switching over to custom mode at which point the magenta cast simply went away. I am usually never a fan of baking in a look preferring to have that latitude to CC in post. But in this case it was the only remedy.

This was a big shoot and there were several tense hours on set trying to get this camera to play nice. Fortunately most of that time was on a pre-light day. What I fear now is that I won't get the call again from this group because my camera was causing problems that I couldn't fix. I was embarrassed and pissed.

Has anyone else on this forum had this happen and what do you do to fix it on set? I was pretty confident we could fix it in post but the client didn't want to risk it. And frankly I don't blame them. The magenta was only in the shadow/black area not in skintone so pushing green overall would have screwed the skintones. All clients want to see a nice image on the confidence monitor at video village. Fixing it in post is a cop out, this camera should be able to resolve a nice image without a magenta cast. Any guidance would be greatly appreciated.

cheers
Kevin
 
Jeeez Kevin, I can feel your pain - that sounds like a complete nightmare situation! It's hard to give any advice to try to find the route cause of the issue with the info you've given. A few extra questions from me:

- Is it safe to assume you were shooting XAVC to XQD cards, or did you have a more exotic recording setup?
- When you "went over to custom mode at which point the magenta cast simply went away", what gamma mode did you go into, STD? It would've been interesting to see if the problem persisted in Custom with Slog3 gamma and matrix switched off. That info could help work out if the issue was caused by Cine-EI alone, or something more subtle.
- Have you tested the camera with a similar (all-tungsten) lighting setup since the shoot to see if you can repeat the problem? I would recommending trying to narrow down variables as much as possible.
- Do you perform your 'maintenance' APR whenever asked by the camera? Did you try a manual APR as part of the troubleshooting process during those torturous hours?

Those points could help clarify what's going on (or might not!). My instinctive suspicion would be something to do with white balance, since that's the major difference between CineEI and Custom. I can't imagine how the lighting would've been tinted to magenta, but stranger things have happened. The particularly strange part is that it's only in the shadows, which might point towards a hardware or software issue with the camera.

If you ARE able to replicate the problem, then I would try an all-reset and re-test to see if that shakes out some soft-/firm-ware gremlin. If it doesn't, then it sounds like it might be time to take the cam to the service centre - SCHEISER.

Sorry to hear about your situation,

jason
 
Ouf I feel your pain. Those situatioms are the worst. Is it your own camera that you handle every day? Is it on FW4.0 or newer?
 
Hi Jason,
I was shooting XAVC-I internally to the XQD cards.

In custom mode with gamma set to STD or Slog3 there was no magenta cast. I haven't been able to try to replicate the situation again.

I have always done the APR when asked by the camera but not part of the troubleshooting. I didn't know that was possible actually.

Did black balance at the start of the day.

It is my everyday camera and on the latest firmware. 4.1 I believe.

I will do a system all-reset and see if that helps.

The main weirdness was that we had 5 room sets going and this magenta cast only materialized on one of them. All tungsten lights in the same studio space in the same day. The only difference was that the offending set was devoid of any color. Left me baffled.

Thanks for the help.

-Kevin
 
Hmm. The WB-axis between green and magenta is supposed to be set in post when shooting CINE-EI, but feels really weird that tungsten light would show magenta. If you had the footage you could try to make a custom LUT that corrects towards green but as you say that did not seem to be the problem here. Your workflow seems solid.

I guess a set devoid of colour would make any slight WB-difference more noticeable. But the fact that it showed only in the dark parts of the image seems weird.

Could it have been moire in the fabric? Could the camera been overheated?

What did you send out from the camera? Did you see it on the camera monitor aswell?
 
Could it be IR or near IR contamination, too low to be noticed on most shots but maybe on a B&W set under tungstun be more obvious? Was it in truly black areas of full shadow or on some dark material which could be more prone to IR? Did you try different lenses or take any footage to review?
First thing I would do is try to recreate it.
 
Here is a still from that scene. Notice when you drop a LUT on it the magenta on the chest at the foot of the bed, the little under bed cubes, and the gray in the pictures. Without a LUT in Resolve the magenta is not as pronounced but still there. The under bed cubes fabric did seem to have a slight magenta naturally to the eye but became much more in camera.

We were in an air conditioned studio so I doubt the camera was overheating.

I did not even think about IR contamination. Maybe.

It was visible on all monitors. 17" SmallHD, camera monitor, 7"SmallHD, and 5"smallHD

-K


Magenta clip.Still001.jpg
 
The image was pretty low res, so I could not really see the problem in resolve. Only a hint was visible.
 
Here, this should help.

Bedroom corrected.jpg

Box at the end of the bed goes very magenta. I don't think it's IV contamination though. Very weird. I've had weird colours in my VF, but not recorded to disc, in fact I just got my VF cable replaced, but I've not seen anything like this. Very odd. Looks like an issue with the optical block, but why only in one set-up. I'm scratching my head...
 
doesn't look like IR I agree. I don't think the box would have it and its all over the place. This should be a dumb question , but did you turn the camera on and off while testing? It is a computer.
 
Yeah I did restart. In fact, it couldn't be heat related because the camera sat overnight in a nice cool studio and the next morning it was still showing the magenta after starting up. That's when we switched to the custom settings.
Just a few minutes ago I did a system restore all settings and then went through and put all my settings back to where they were when this started and I cannot get that magenta to show up again.

-Kevin
 
Dumb question... You said you were shooting tungsten in a studio, but was it true tungsten or did you just mean 'tungsten' as in ~3200K source and the actual lights were LED or Flo's? Another thought I had was possible light pollution if there were instruments of different technology being used(mixing tungsten, LED, Flo's), but still the same 'color temp'.

But after looking at the image, I don't think that is it, either.
 
I'm also curious if these were traditional "true" tungsten units or maybe tungsten balanced flo's or LED's. I noticed FS7's tendency to render neutral grays and blacks as brownish / magentaish shades under certain lighting conditions in Cine EI, this often happens with specific fabrics which normally appear black to a naked eye. Under the same lighting conditions other "true black" objects such as plastics, other fabrics, etc are rendered without the skew towards magenta, which tells me that there must be something in the fabrics that come out magentaish that actually has a touch of this color which our eyes (and sometimes other cameras) don't see. In particular, this happened to me when I used GE's "Reveal" series tungsten bulbs, just a touch of magenta, which I discovered they have in the spectrum, makes the camera respond in that exaggerated way. More precise WB in Custom mode takes care of it, but it is easy to replicate the problem even there by warming up the image under WHITE setting - this suggest that it's the imbalance of the red channel which triggers it.

Not to go off topic too much, I want to mention something that is likely related. I discovered that in FS7 there seems to be a "breaking point" with WB - point at which camera starts to somewhat abruptly render colors differently - the change does not seem to happen proportionally / linearly to the temperature shift. I wrote about it at DVINFO, I had a blue fabric which by a small WB change would either be rendered blue or very purple. It's this tricky blue color which traditional film stocks had a problem representing correctly because it falls in the part of the spectrum where blue and red film layers overlap. Something similar happens with FS7. I then saw a TV show "Vinyl" which was shot on F55. There is a scene in which Bobby Cannavale wears a blue shirt - exact "tricky" color which I described and had trouble with - the shirt looked purple in one angle and blue in a reverse shot, very visibly different. That's because one side was lit with a light of a slightly warmer temperature - the effect of that difference was not proportional, greatly exaggerated.
 
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