C300 MkII ISO Colour Shifts at DVinfo.net
DV Info Net

Go Back   DV Info Net > Canon EOS / MXF / AVCHD / HDV / DV Camera Systems > Canon Cinema EOS Camera Systems
Register FAQ Today's Posts Buyer's Guides

Canon Cinema EOS Camera Systems
For all Canon Cinema EOS models: C700 / C300 Mk. II / C200 / C100 Mk II and EF / PL lenses.

Reply
 
Thread Tools Search this Thread
Old December 7th, 2016, 07:42 AM   #1
Regular Crew
 
Join Date: Jul 2008
Location: London UK
Posts: 50
C300 MkII ISO Colour Shifts

Hi, I'm noticing quite a colour shift when changing ISO. Even when quite a small change - going from ISO 1000 to ISO 1250 there is quite a shift from a red bias to a green bias - as shown in this link -

I've also noticed some strange colour banding, as shown in the attached image.

Anyone else have similar, or any idea what's causing these issues? Thanks,

Matt
Attached Thumbnails
C300 MkII ISO Colour Shifts-c300ii-colour-bands.jpg  
Mathew Williams is offline   Reply With Quote
Old December 8th, 2016, 11:12 AM   #2
Trustee
 
Join Date: Oct 2001
Location: San Luis Obispo CA
Posts: 1,195
Re: C300 MkII ISO Colour Shifts

Hi Matt,

It would be great if you could give us more information concerning the footage. What gamma setting were you using? Also is the footage graded in anyway?

First culprits would be ABB....did you Auto Black Balance before shooting this? The banding you are seeing would appear to be CMOS smear caused by the highly overexposed area and usually seen in the darkest shadow tones. (the darkest shadows are also the place where you usually see color shifts in one direction or the other on this camera, ABB can help to clean that up.) Without know what you did to the footage or what gamma you used, it's hard to tell, but if I had to guess, the color switching between ISO changes is not that unusual in this case. This footage is extremely limited in it's range....all we see are areas that are over and underexposed in the same shot and we are looking at an area that, once graded, should be rendered as black. You may be testing the limits of the cameras range here. How bout a fill card? :-)
__________________
Barry
http://www.barrygoyette.com
Barry Goyette is offline   Reply With Quote
Old December 8th, 2016, 02:28 PM   #3
Regular Crew
 
Join Date: Jul 2008
Location: London UK
Posts: 50
Re: C300 MkII ISO Colour Shifts

Hi Barry, thanks for the reply. The settings were Clog3, production camera, BT709. The video clip hasn't been graded at all (but I did scale in to 130% just to crop out the person in shot to protect their privacy). This was an event shoot so no lighting used, or time to be using bounce panels etc. I was just interested to see this colour shift and so thought I'd ask about it. I actually noticed the same thing on a shoot yesterday as well. I did an ABB a few days ago, maybe that changed something - I will try doing another though not sure why that should change anything?

The still image has had the midtones raised in post just to make the smear stand out more clearly - thanks for the explanation it is somehow caused by the area of overexposure - are you able to explain a bit more about why this happens, and why it shows up in the dark area?

Thanks again.
Mathew Williams is offline   Reply With Quote
Old December 8th, 2016, 07:40 PM   #4
Trustee
 
Join Date: Oct 2001
Location: San Luis Obispo CA
Posts: 1,195
Re: C300 MkII ISO Colour Shifts

Hi Matt,

So...in general, you want to do an ABB every time you fire up the camera, typically wait for 20 mins or so for it to warm up and then do it. I also find it's helpful to take a hard look at your shadows after ABB to make sure things are looking neutral. If not, ABB again. The shadow end of a log gamma is looking at the most fragile, noisy portion of the sensor readout, and it will exhibit color and noise changes based on changes in temperature and also image processing, (which changing the gain or "ISO" is) and so doing the ABB is going to at least balance the image before you get started.

Now...typically shooting in log gamma you are going want to try to "shoot to the right" a little so that your image is light, and shadow areas can be pushed darker in post. Raising mid-tones in LOG is generally the opposite of what you're supposed to be doing.

CMOS smear is caused by overexposed areas (smarter minds than me can explain the electronic aspect of this), but is visible in the darkest shadows that are adjacent to or in line with those overexposed areas...again if your workflow is correct, rarely is it seen in graded footage as it's in the area you are generally crushing to black or near black. Cmos smear is visible to some degree on almost every camera with a cmos sensor, although the C300markII seems to exhibit it more in Log2 than other cameras.

Here's where it gets interesting...your first problem...the color balance changes in the shadows when you change ISO...welll that may just be CMOS smear caused by upping the gain on an already saturated highlight. We're not seeing the telltale line there because the highlight runs the full hight of the frame.

Just so you know how common cmos smear is...when you look at a DSC Labs Xyla dynamic range chart you'll notice a peculiar wedge shape to the graduated steps of the chart. The purpose for this wedge shape was to avoid misreadings due to CMOS smear, as the chart is designed so the first step is always clipped. That step is smaller in height compared to the darker steps, so any smear affects only the center of each of the darker steps allowing for a proper reading of the margins to ascertain DR of a camera.
Attached Thumbnails
C300 MkII ISO Colour Shifts-picture-11.png  
__________________
Barry
http://www.barrygoyette.com
Barry Goyette is offline   Reply With Quote
Old December 9th, 2016, 12:52 PM   #5
Regular Crew
 
Join Date: Jul 2008
Location: London UK
Posts: 50
Re: C300 MkII ISO Colour Shifts

Thanks Barry, that's very informative and good advice regards the ABB and waiting for the camera to warm up before performing it. I will try this and see how I get on. Thanks!
Mathew Williams is offline   Reply
Reply

DV Info Net refers all where-to-buy and where-to-rent questions exclusively to these trusted full line dealers and rental houses...

B&H Photo Video
(866) 521-7381
New York, NY USA

Scan Computers Int. Ltd.
+44 0871-472-4747
Bolton, Lancashire UK


DV Info Net also encourages you to support local businesses and buy from an authorized dealer in your neighborhood.
  You are here: DV Info Net > Canon EOS / MXF / AVCHD / HDV / DV Camera Systems > Canon Cinema EOS Camera Systems


 



All times are GMT -6. The time now is 03:53 AM.


DV Info Net -- Real Names, Real People, Real Info!
1998-2024 The Digital Video Information Network