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  • 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 calibration question

Christoffer Glans

Christoffer Glans

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So I'm trying to do a correct black calibration and there are some things I don't understand. First of, at ISO 12 500 there seem to be a purble shade on the right side of the image (it's there when recording). I know that 12500 is a bit too high, but should there be a color shift/shade when it's calibrated? It was really bad when I got the camera, but after a calibration it's better. Still I wonder why it's still there?

Second, when I do the calibration, I set my exposure to what I normally shoot, I set the camera in complete darkness, aperture closed etc. but then I should choose "current fps/exposure", but even if I have choosen 25fps, the black calibration change it to varispeed 25fps instead. Shouldn't "current fps/exposure" set it to exactly what I've set it to?
 
Bump, I'm not sure if this is common or not?

Also, the question about black shading "current exposure". Why does it go to 24fps varispeed when I have the fps and timebase on 25fps?
 
Christoffer Glans said:
I set the camera in complete darkness, aperture closed etc.
Click to expand...
I know this is not answering your point, but you really should remove the lens and attach the RED Body Cap. Closing the aperture does not block light from the sensor.
 
Christoffer Glans said:
Bump, I'm not sure if this is common or not?

Also, the question about black shading "current exposure". Why does it go to 24fps varispeed when I have the fps and timebase on 25fps?
Click to expand...


Unknown to the common mane, but happens on Dragon every time

Thank you very much

Fury
 
Don't know about the 24 varispeed thing.

But let the camera record half a mag or so until it gets up to working temperature.
Then do the blackshade. Lens cap on and black sack over lens or remove lens and use the mount cap.
A perfect black shade would give you a uniform gray frame on the screen when set to 12800iso. A little bit of none uniform or even tinted slightly to the side does not matter much if you exposure is good. Basically the black shading is doing more difference to the far left of you histogram.

The black shade go by exposure time and temperature. So for example making a black shade for 50fps at 360 shutter will give exact same result as 25fps 180 shutter. A cold camera will need a different blackshade then a hot camera and so on.

But honestly I never had mutch fuss with it. If I shoot high speed green screen poorly lit and long exposures then yes a black shading for that fps and current temperature is needed. But except for that I pretty much just blackshade after upgrades.

Cameras can come from red new and after service not blackshaded.

The fps thing is possibly so that it always record the BS sample footage at 24fps but use the exposure time to adjust to get to current fps... A trick to test it would to do a blackshade for current framerate at 3fps or such but possibly then it still does it at 24fps but use frame summing to get the exposure to 3fps as it would possibly take quite a while if it did it at 3fps.

Thats me guessing around the subject, lol.
 
I've done the black shade exactly how it's supposed to be done. Though I'm still seeing a slight shift in brightness on the right side of the image at 12500. I used the cap on the lens, completely dark room with aperture closed and the lens area covered with a black cloth (not blocking the fans). It can't be more dark than that.

The only thing I'm really interested in is if the slight gradient av brightness on the right side of the image at 12500 is normal even after a correct black shade? I mean, should the image be totally uniform at 12500 or might there be some changes?

Thing is that I'm experimenting with shooting at 12500 and doing advanced noise reduction to see how good I could get the image. But the slight brightness change will still be there after noise reduction.
 
I would try it all again with a cap on the body.
When you record absolute black you still may be getting light leak from the lens or the mount. (Not sure what mount you are using)
do you lift off the black sheet when you record? At those ISO's it could be light leak. Double check that the mount is fixed tight (do not reef it) and double check with the cap instead of a lens which even at f22 capped could be leaking light in (not during the black shading but when you record if you lifted the cloth off)

12800 ISO experiments sound cool. Would be interested to see the results. Have seen anything shot at 12800iso on epic.

Battistella
 
Christoffer, although you've set 25fps timebase and exposure, the camera still shows 24fps varispeed on the display during calibrating the blacks. The camera gets still correctly calibrated for 25fps –or, at least, the name of the calibration file shows the camera has recognised the correct frame speed.
 
Christoffer Glans said:
I've done the black shade exactly how it's supposed to be done. Though I'm still seeing a slight shift in brightness on the right side of the image at 12500. I used the cap on the lens, completely dark room with aperture closed and the lens area covered with a black cloth (not blocking the fans). It can't be more dark than that.

The only thing I'm really interested in is if the slight gradient av brightness on the right side of the image at 12500 is normal even after a correct black shade? I mean, should the image be totally uniform at 12500 or might there be some changes?

Thing is that I'm experimenting with shooting at 12500 and doing advanced noise reduction to see how good I could get the image. But the slight brightness change will still be there after noise reduction.
Click to expand...

One way of doing advanced noise reduction is to shoot a black clip at the given high iso and make a compound over multiple frames then you get a so called "black frame" then you use the black frame negated to push out all all the gray or push up all the black, basically neutralize the difference over the sensor.

Better than that is to do the same with every channel separate and apply to footage as separate channels As the blue green and red are all very different.

A slight magenta shift on the screen at 12500iso is no big deal what you see there is not much of use any way if you want to create a good image I think it's safe to say that those values should be pushed down to 0,0,0.
 
Björn Benckert said:
One way of doing advanced noise reduction is to shoot a black clip at the given high iso and make a compound over multiple frames then you get a so called "black frame" then you use the black frame negated to push out all all the gray or push up all the black, basically neutralize the difference over the sensor.

Better than that is to do the same with every channel separate and apply to footage as separate channels As the blue green and red are all very different.

A slight magenta shift on the screen at 12500iso is no big deal what you see there is not much of use any way if you want to create a good image I think it's safe to say that those values should be pushed down to 0,0,0.
Click to expand...

Yeah, I've only tried the Neat video method which works impressively well and fast. But if the "black frame"-method is better, how do I do it? Is there any plug-ins for AE/Resolve that manage this or is the method custom made?
 
Christoffer Glans said:
Yeah, I've only tried the Neat video method which works impressively well and fast. But if the "black frame"-method is better, how do I do it? Is there any plug-ins for AE/Resolve that manage this or is the method custom made?
Click to expand...

You have to fiddle with it. Make a AE setup (i done it in flame before but could not find it now) The thing with using a black frame is that you actually got info of whats noise and whats uneven sensor patterns. Neat video is a advanced "noise remove" that treat RGB separately but smears the color channels so to get the most out you would do the black frame and then neat video or similar.
 
Björn, if I understand you well, you first suggest to take a black sample averaged over frames many enough. Then this so called black frame, which is a representative of average noise and non-homogeneity of the sensor, is subtracted from the actual clip.

Speaking about Neat image it is possible to employ noise samples in their still image software. Consequently, with your 'black frame' -approach one can first generate a calibration file, and then exploit this camera-specific calibration to remove noise frame-by-frame with the still image software. Works out automatically at least in Photoshop with the batch mode. My guess is, the result is even better than that of Neat video.
 
Lauri Kettunen said:
Björn, if I understand you well, you first suggest to take a black sample averaged over frames many enough. Then this so called black frame, which is a representative of average noise and non-homogeneity of the sensor, is subtracted from the actual clip.

Speaking about Neat image it is possible to employ noise samples in their still image software. Consequently, with your 'black frame' -approach one can first generate a calibration file, and then exploit this camera-specific calibration to remove noise frame-by-frame with the still image software. Works out automatically at least in Photoshop with the batch mode. My guess is, the result is even better than that of Neat video.
Click to expand...

Correct.
But neat video also use "denoise algoritms" and apply them to taste in rgb. So a combo of the two would do best.

My guess is that the ADD could work a lot better if RCXP got a sample of the used blackshade aswell. But maybe that is allready in practice.
 
Björn Benckert said:
You have to fiddle with it. Make a AE setup (i done it in flame before but could not find it now) The thing with using a black frame is that you actually got info of whats noise and whats uneven sensor patterns. Neat video is a advanced "noise remove" that treat RGB separately but smears the color channels so to get the most out you would do the black frame and then neat video or similar.
Click to expand...


How do I make that AE setup for this? If I have a black sequence of a few frames at the same ISO, fps and resolution, how do I apply it as a noise canceller?

Antony Newman said:
What David said.

+) Lens covers don't necessarily block IR
+) Lens allow some stray light through the cap.

AJ
Click to expand...

In a complete dark room with a black cloth over everything but the fans?
 
When I black shade I put the lens cap on, then I take an empty filter case and put that around the lens mount, then I put a sweatshirt around the whole front of the camera propped up by the rails and held to the front of the lens by the matte box. I know it sounds a bit ridiculous and it might even be overkill but I've never had a problem with my black shading!
 
Marcus Friedlander said:
When I black shade I put the lens cap on, then I take an empty filter case and put that around the lens mount, then I put a sweatshirt around the whole front of the camera propped up by the rails and held to the front of the lens by the matte box. I know it sounds a bit ridiculous and it might even be overkill but I've never had a problem with my black shading!
Click to expand...

Can't you find a dark room? I do my black shading in the bathroom :laugh:
 
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