Welcome to our community

Be a part of something great, join today!

Log in
  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Black shading - questions and thoughts

Petri Teittinen

Petri Teittinen

Well-known member
Joined
Apr 29, 2009
Messages
988
Reaction score
0
Points
0
Age
58
Website
www.saitti.org
Mr. Marchant's fantastic graphs made me think about black shading and the implications of heat.

Setting aside for a moment the fact that I don't quite understand why RED's cameras need black shading when competition does not (or do they?), I got to worrying about the temperature range where black shading applies.

The shooting temperature range appears to be from 40 to 75 degrees Celsius. That's quite a wide range and it feels to me that a black shading done at 40 degrees can not be valid all the way up to 75C (although I could just as easily be wrong about that).

This thinking lead to questions.

- If I perform black shading at 40 degrees and begin a long take, how high can the temperature rise before I might see problems in the image?
- Should I run the temp to 60-65 degrees before black shading if I knew in advance the takes will be long?
- Alternatively, would a black shading closer to 40-45 degrees make sense if I knew in advance the takes will be short (and far apart, with enough idle time to allow for cooling)?

I'd love to see RED introduce a sensor certification feature and some sort of dynamic black shading which would rid us of the need for black shading. Here's how I imagine it might work: (Warning! Non-engineer rambling ahead!)

1) Connect EPIC/SCARLET to a power source with enough juice to run the camera for a couple of hours non-stop.
2) Make sure no light gets to the sensor.
3) Boot camera up, insert REDMAG, enter Maintenance Menu and select "Sensor Certification"
4) The camera begins running a series of automated black shadings at different frame rates, resolutions, shutter speeds and temperatures. This will take quite a while.
5) As a result, a large-ish data file is saved on the REDMAG.
6) Copy the file from REDMAG to your PC/Mac. Download & install a "Black Shading Calculator" software application from RED and load the data file into the app.
7) Based on the data file's contents, the application creates a black shading file which is then copied to a REDMAG and loaded into the camera.
8) The camera now "knows" how its sensor behaves in various different scenarios and operator-performed black shading is no longer needed.

One can dream, right?
 
AFAIK most cameras do a blackshade on startup. For some reason RED's way of doing a black shade takes a bit longer.

On Marchant's graphs the sensor temp never goes much higher than 40. The core temp goes up to 75, but that doesn't have an effect on blackshading, only the sensor temp matters.
 
Jaakko Rinne said:
On Marchant's graphs the sensor temp never goes much higher than 40.
Click to expand...
Ah, indeed. The sensor temp variance is 31-42 degrees, according to the graph. But that does not change my question any: how sensitive is the sensor to temperature changes? Should black shading be done at 40 degrees when doing long takes and at 32 degrees when doing short takes with plenty of time for cooling down between takes?
 
I think in an earlier thread there was talk about a difference of 5 degrees and up being where blackshade might start to make a difference, but even then it depends on what ISO you intend to use, if you'll be crushing blacks and also if you're shooting tungsten or daylight. I've done the blackshade on my Scarlet-X at 40 degrees, since after the camera has been on for more than a few minutes the temperature won't be too far from that and won't rise much higher even when recording a longer take. For a shoot outside in colder weather I'd probably test where the temperature settles and do a blackshade at that temp if possible.

Haven't had problems shooting in the studio with the camera running for hours or run and gunning with the camera recording as soon as it boots up, but I've also never had to go above ISO 1600 and have always tried to stay at 5600K. It might be useful if someone had the time to do some blackshade vs. temperature tests.

EDIT to add: I'd personally like to see an option to set the fans to automatically try to keep the sensor/core at a set temperature. If the temp stayed the same, this would be a pretty moot discussion.
 
Last edited:
Jaakko Rinne said:
even then it depends on what ISO you intend to use
Click to expand...
How come? As I understand it, ISO on RED cameras does not work like it does on, for example, DSLR cameras. ISO setting on Epic and Scarlet does not alter sensor sensitivity or gain. ISO setting is just metadata, in other words.
 
Jaakko Rinne said:
EDIT to add: I'd personally like to see an option to set the fans to automatically try to keep the sensor/core at a set temperature. If the temp stayed the same, this would be a pretty moot discussion.
Click to expand...

+1

How does ISO affect blackshading? :

You can see good or bad blackshading when pushing iso and digging info in the noise area, and there fore it does depend if you entend to use 3200 iso or 320 iso as the base, and this will change how critical it is to have the right blackshading.

Pat
 
I understand that this is an appropriate technical discussion and it would be good to get some detailed technical answers.

However, I have kind of let the whole black shading thing go. I only black shade when there is a pretty extreme change in temperature anticipated. I have not black shaded very much at all and have not noticed any particular problems with my images at all.
 
Petri Teittinen said:
How come? As I understand it, ISO on RED cameras does not work like it does on, for example, DSLR cameras. ISO setting on Epic and Scarlet does not alter sensor sensitivity or gain. ISO setting is just metadata, in other words.
Click to expand...
Like Patrick said, with a higher ISO you're moving middle grey lower into the signal and essentially boosting or lifting data that is nearer to the noise floor. Boosting the lowlights makes noise become more prominent, thus making the effect of a good or a bad blackshade more prominent as well.

Enrique: Sensor/Core temp is on screen at all times if you have the menus enabled.
 
Erich Ocean said:
As I understand it, the Canon C300 is blackshading continuously, using the look around area. This is why it's so killer in low light.
Click to expand...
Is this even possible? Isn't the point of the blackshade to map the noise pattern of the entire sensor so the map can be used to substract the noise pattern from the signal? You can't really do that from the look around area.
 
Jaakko Rinne said:
Like Patrick said, with a higher ISO you're moving middle grey lower into the signal and essentially boosting or lifting data that is nearer to the noise floor. Boosting the lowlights makes noise become more prominent, thus making the effect of a good or a bad blackshade more prominent as well.
Click to expand...
Hmm. There's so much conflicting info on this subject here on reduser it's getting kinda hard to know what is what.
 
It is worth while doing your own testing. A really good test is just don't do a new black at all and try shooting for yourself in a number of radically different conditions. I became a lot more relaxed about the necessity for black shading after I did this.
 
I too am pretty relaxed about black shading. I generally do it after a firmware upgrade and at the start of a big project. I do not tend to film in extreme environments so I do have it easy in that respect.

However, maybe you more technical people can explain this:

On a recent 3D project, I noticed that the histograms on my two Epics were showing a stop difference in exposure between the two cameras as were all the exposure aids ( false colour etc). The stops WERE the same as were shutter and anything else that could affect exposure. After puzzling over this I checked with the DIT who said the RAW exposures were correct on both cameras but suggested that I do a black shade. I didn't understand why but did it anyway and problem solved. identical histograms on both cameras. We could not see any difference in the quality of the RAW files before and after the Black shade.

Methinks the Black shading process does rather more than simply provide a measurement of sensor noise levels.

David
 
Haven't noticed any issues since Red One
I do not mind black shading before most shoots
It's a professional tool..
 
So has the problem gone away with later versions of camera firmware?
I ask because not long ago the advice was to do black shading before changing shutter speeds for different frame rates,
and to let the camera warm up first, which adds up to a 40 - 45 minute delay before shooting can commence.
This seemed absurd....
 
Are you guys having this much noise trouble?
We black shade when upgrading and when doing long exposures, but that about it. Have no noise issues.
 
You must log in or register to reply here.
Back
Top