C300 MKII: Purple Lines appearing

[Aidan J Maguire]

Has anyone else experienced purple lines appearing in shadows of back lit C300MKII footage? I found this to occur in CLog 2/3 Cinema Gamut @ ISO 800. I black balance the camera regularly during a shoot - every lens change / ISO change - every time I can, as recommended by Canon. Is this 'normal'? It seems that this camera does not like back lit scenes.

Here is a sample frame grab: https://flic.kr/p/SdLajw

[Gary Huff]

What firmware version are you on?

[Aidan J Maguire]

Hi Gary, I'm using the latest firmware: 1.0.6.1.00

[Aidan J Maguire]

Another example: https://flic.kr/p/SBwKq8

[Mathew Williams]

Hi, I raised this (or something similar) recently -

http://www.dvinfo.net/forum/canon-ci...ur-shifts.html

I was seeing it as a white balance shift when changing ISO with the image becoming more purple or green as the ISO is switched. But actually I think it's the same as you're seeing - if you look at the last bit of my video clip you see the purple lines down at the bottom of frame.

[Aidan J Maguire]

That's not good at all. Were you able to learn anything more about this / work arounds? (I read your thread).

The purple line issue has appeared on a number of my shoots. Very concerning...

[Pete Cofrancesco]

Originally Posted by Aidan J Maguire

Another example: https://flic.kr/p/SBwKq8

While you were scrutinizing the purple lines you missed the murder taking place in the apartment across from you.

[Aidan J Maguire]

I appreciate your input Pete. I'm not pixel peeping here... Purple lines are still seen in grade when shadows are crushed / LUT applied.

[Dan Parkes]

Hi Aidan

I feel your pain. I've experienced exactly the same issue, except it was in the shadows of the face of an interviewee, with no chance for a reshoot! Despite having a 1080p monitor we did not pick it up on location as we were battling radio mic frequency interference and location logistical issues (well that's our excuse). To then ironically find we actually had far worse visual interference. And of course, it was not until the grade where it became very obvious. Had to do a lot of post rotoscope grading that was painful and never really got rid of it.

At the time we were shooting in Clog2 primarily BT.709, BT.2020 (and possibly C.Gamut) but as it was a year ago I cannot remember precisely, with ISO between 800-1250, shutter normally close to wide open (2.8) for DOF. We do regular ABBs. I also found there was a lot of noise in the blacks in Clog2.

After that truly awful experience, I went straight back to good old reliable C-log and not touched C-log2 or 3, or anything with "BT" in it ever since! And been very happy. I was really hoping the firmware upgrade would have sorted it, if I ever decided to try again.

[Travis LaBella]

I've experienced the exact same issue with purple banding in shadows the last few months. It appears fairly regularly when backlit - this has been across multiple firmwares and multiple Clog2 and Clog3 settings. I've also noticed it on rental C300 Mark II's. I consistently ABB before shoots.

It's often hard to catch in the field unless you're looking for it, and then will become more noticeable in post with a LUT applied.

Has anyone remedied this solution? Is this something that has been addressed by Canon or something Canon is able to service?

Thanks!
Travis

[Barry Goyette]

I'll be honest...we've seen this kind of CMOS smear from this camera since the earliest shown prototypes. I don't think it's something that is going to go away on Canon's end. Many cameras exhibit this phenomena to some extent or another. As Canon has expanded it's DR to within an inch of the C300mkII's life, it's probably going to show it more than some other cameras.

Ways to avoid it? I think it's an honest assessment that when one purchases a 15 stop camera that you'd hope to get to use all of that DR in your shots. The reality is that, unless you are shooting for HDR, and who is, really, at this point, you are going to be finishing your shots in Rec709 with about 6-7 stops of DR. So should you really be "exposing for the exterior" like this and then obsessing about the purple lines in the dark interior shadows? It's not a good strategy with any log gamma image, but especially with a camera like the C300 mark ii which excels when the captured image looks generally brighter than the finished result. (Do a test of a scene with a moderately high level of contrast (with some actual light on focused objects on the foreground) -- expose it at say ISO 800 hoping to bring it up in post, and then at successively higher ISO's without changing exposure. Grade back all the images to look "right" (eventually you'll start bringing the midtones down instead of up) and see what starts to happen to the noise. You may be surprised that an image shot "brighter" at ISO 2500 or 6400 or even 12,800 can look surprisingly cleaner than one exposed at a lower ISO but darker. This is part of Canon's special sauce and you need to try it.

Secondly. If you expect to see a full range of detail outside the window and have a usable range of tones on the inside of a curtained room like this, you're gonna have to turn on a light. DP's shooting on an Alexa show up with truckloads full of 10 and 20ks to shoot scenes like these. There is no magic camera that is going to hold it all, that you can then beautifully compress into an output gamma like Rec.709 without lighting that interior, or ND-ing the windows, or throwing away either the highlights or shadows or both.

You probably don't want a primer on Day interior lighting, but if you do, turn no further than Roger Deakins on No Country for Old men -- scroll about a third of a way down to see a series of Day-Int shots and a description of the lighting. It's revelatory. No Country for Old Men | CineGleaner

You need to get your shadows up (in camera) and use all that DR for power windows and recovering highlights, which is what it's for.