NX1 exposure drift problem FIX

[Steve M.]

Huh? You're kidding me, the 45mm drifts out of focus? Is that the lens or the body itself causing that? Also, I'm curious to ask the Drifters, sorry my sick humor, people experiencing the drift, if you actually are seeing that bloom in the LCD and or viewfinder?

[DigitalEd]

Ok here is some of the 69 gigs i shot today i converted a few clips to make this. It has color grading i added might be a little to bright on a few clips. As the clouds moved the exposure changed every few seconds at times..

 

[Brian Luce]

No pan no tilt no crane no steadycam ect...??? tell that to clients and try to stay competitive. 

 

​I can overcome the camera's limitations with my artistic talent and the fact I can now swap AEL and AF On buttons with firmware 1.2.. Not to mention all the cool new apps I can download. 

[DigitalEd]

Dont count on it... I i am seeing my 16/50 drift out of focus very easy so much so i may not use a Samsung lens when shooting video in any Manual focus setting. Seems to be that fly by wire focus system they use for the lens it drifts very easy. The 45mm is useless for manual focus it drifts out so fast. Get some adapters and cheep prime lens and one good 2.8 zoom from Nikon to use on it. The 16x50 is still a great lens for photography. Unless if this new feature will hold the focus in place for you forcing the lens to lock that focus in and not let it drift then that would be a good plus - i need to test that.  

[agolex]

 

​He is being sarcastic noa.

 

​I don't think he was.

[agolex]

Ok here is some of the 69 gigs i shot today i converted a few clips to make this. It has color grading i added might be a little to bright on a few clips. As the clouds moved the exposure changed every few seconds at times..

Looks fine to me! 

[agolex]

For all our bloom buddies. Get your daily dosage of "bloom" from this sweet footage by Alan Dang (at around 34 seconds). Download the 3GB file and you feel like being in a techno club. :D

 

[noa]

At 30 sec where that surfer walks across the screen there is a obvious flicker, I"m baffled that the guy who shot the film doesn't even notice. It looks like it only happens on quite extreme contrasts.

[agolex]

Yeah, I've been lead to believe that it's also an issue of perception. What some people see as normal is outrageous to me.

Did some more tests with the Auto modes. Obviously with a manual lens, shutter priority is pretty manual (just the ISO is auto). But still, the drifts happen once stuff gets just a liiiittle bit to bright to the NX1's liking. So, if you keep everything dark, there is no shifting. Then, with DigitalEd's latest footage, in the beginning there's obviously blown out highlights in the tent, but I can't see any drifting.

This camera is pure software mayhem for me right now, dunno. Camera says the update is available, but can't download it anywhere. Still waiting so I can try it out, don't feel like using the 'unofficial' version Ed posted before. I do want to return the camera, if the update doesn't fix the issue for me.

[GXAlan]

You know, I didn't even put flicker and exposure drift together -- I just thought it was a flicker and had imagined the exposure drift as being something different in my mind.  There's definitely exposure drift.

I ran some numbers on the still frames from ProRes clips exported as 16-bit TIFFs.

Two bright frames (L / R / G / B average + SD).  The total range is 0-65535

A. 48059 + 17964 / 44718+17233 / 46517+17824 / 47545+18283
B. 48059 + 17967 / 44718+17235 / 46517+17824 / 47545+18285

So it's pretty close.  Then you get to the flicker.  First, the brightness drops by 1.18%

C. 47288 + 17952 / 43497+17231 / 45746+17810 / 47031+18252  (total range is 0-65535)

Then the red frame gets messed up with the range from 257-65535 instead of 0-65535

D. 47288 + 17951 / 43974+17233 / 45746+17810 / 47031+18252

The error in the lower limit of the red channel suggests that there may be an encoding error.   I'm going to see if I can transcode directly to TIFFs instead of ProRes and will follow-up.

[GXAlan]

Ok, exporting the HEVC to TIFF directly, skipping the ProRes. 

1) All channels DO show 0-65535 range.  So ProRes is making it worse.

2) The flicker is visible on source HEVC as well.  Here are the median values L/R/G/B (i'm skipping the standard deviation)

 

TIFF   A 48059 / 44461 / 46260 / 47545

ProRz A 48059 / 44718 / 46517 / 47545  

TIFF   B 48059 / 44461 / 46260 / 47545

ProRz B 48059 / 44718 / 46517 / 47545

(overall brightness is the same, but it is slightly higher on ProRes.  Would be one tick in 8-bit 0-255 scale)

 

TIFF   C 47288 / 43690 / 45489 / 46774 

ProRz C 47288 / 43497 / 45746 / 47031

TIFF   D 47288 / 43690 / 45489 / 46744

ProRz D 47288 / 43974 / 45746 / 47031

So compared to ProRes, the overall brightness drops the same 1.18%.  However compared the ProRes is a bit brighter in green/blue and darker in red.

I compared the frames and then did an stretched the histogram.

 

So there you go.

[agolex]

Impeccable, Alan, now we have something mathematical, too. I prefer to rely on my perception, but this should undermine matters. I doubt it has to do with encoding, though, it's just the camera doing what it likes to do when things get bright. Samsung were probably trying to protect the highlights, but didn't set things up properly.

[GXAlan]

** Since I cannot edit the earlier post.  The first set of 3 images are EXAGGERATED with a stretched histogram to highlight the differences visually. The second set of 3 images are the true linear difference from the subtraction) ***

 

But TBH, with exposure drift I was imagining more of the auto-exposure effect -- we should probably call it "flicker" instead of exposure drift so people understand that it's a tiny difference.  I sometimes think of flicker as shutter issue.

What's interesting is that you're looking at only 3 points of brightness a 0-255 scale which is TINY.  The Samsung is probably running 12-bit ADC in video mode.  0-4096,  So it's probably 48 point difference in 12-bit.

Given the average scene brightness in frames A/B, the image C/D are only darker by 0.02 eV.  I don't remember what the electronic shutter is like but it's possible that the 1.2% variation in the e-shutter is enough to cause this problem?

The other possibility is that most CMOS sensors have black pixels which are used to automatically calibrate the black level.  As the sensor heats up (i.e. light on a black surface") it potentially may convince the sensor that it's too hot and then it recalibrates itself on the fly.  If the sensor and CPU are fast enough that it's recalibrating in real-time for every frame, maybe when shooting into the sun, it heats up the sensor just a little bit.

If Samsung does a true exposure lock, it probably won't flicker but over a 30 minute recording, you may end up with more noise or the opposite where it slowly gets brighter as the sensor heats up. We see this with the 5D Mark II and extended shooting -- it gets noisier.  If this is the problem, I'd probably tell Samsung to give owners the power to make the customization. You could do a moving average where it waits for a number of frames to show increased heat before adjusting the black level or Samsung could do a more gradual ramp up/down such that if it detected increased heat, it would +1 the compensation each frame.

Read noise and Thermal noise on the Samsung is pretty good though.  

ISO 1600 NX1
Two 1/8000 bias frames: StdDev 11.4
Two 30 second dark frames: StdDev of 22.3

ISO1600 A7R
Two 1/8000 bias frames: Median difference of 0 on a 16-bit scale, StdDev 5.7
Two 30 second dark frames: Median difference of 0, StdDev 13.029

Sony's noise increases 2.29x. Samsung's increases 1.96x only (even though there's more inherent noise at baseline -- it's APS-C and more densely packed?)

From a read-noise perspective, NX1 is pretty good too.

NX1
ISO100 3.14 e-/pixel (SD 7.9 e-)
ISO1600 1.68 e-/pixel (SD 4.0 e-)

A7R
ISO100 2.73 e-/pixel (SD 81.4 e-)
ISO1600 2.19e-/pixel (SD 4.7 e-)
 

My gut says that when the inherent noise is so low, thermal noise (from light) may be higher than we're used to dealing with...  I sent an email to Samsung.

[agolex]

Good luck with getting a suitable reaction or even attention with that high specificity.

[DigitalEd]

Would that into the sun shot not have something to do with the fact that it is way over exposed for that much light coming into the camera. That must of been around F32 or beyond that if shooting video at around 50 shutter speed with no ND filter on the camera.

Would this not be user error expecting a shot like the to be handled well with no ND filter pushing any camera past its F stop range for the bright sun area ?. It dose say in the Manual not to point the camera into the sun. I think any camera you buy says that in the manual for good reason.

So if you do what they tell you not to do what can you expect. The only way to get that shot right is with a ND filter on the lens to knock the F Stop down to a manageable range. 

 

[agolex]

IMHO it would not, no. Every half-decent camera should be able to handle this. At least everything else I've used before can.

[Brian Luce]

IMHO it would not, no. Every half-decent camera should be able to handle this. At least everything else I've used before can.

​Agree

[DigitalEd]

Shooting photography if you shot that shot into the sun you would have your shutter speed super high you can not do that with video so you need to use a ND filter

Here are some videos on why you need a ND filters out in the sun.

 

 

 

[neosushi]

Shot a lot with a GENUS ND Filter. Very nice filter. The only thing I disliked was the X pattern at very high ND value. 

Other than that it was great to use (Samsung 16-50 f2-2.8)

 

[DigitalEd]

IMHO it would not, no. Every half-decent camera should be able to handle this. At least everything else I've used before can.

​So why would you even be shooting things that are so over exposed when you could shoot then right using the right tools to get the better shot. That shot into the sun needs a ND filter for any camera you would use no matter what camera it is to get the exposure right for Video..

(Every half-decent camera should be able to handle this) this is not true how can any camera handle F32 or better at 50 shutter speed its way over exposed. Can you look right into the sun with you eyes wide open and handle it at F32 or higher it would damage your eyes in a shot amount of time.

You can not expect a camera or anything to handle things beyond its limitations.

If its F32 in the bright sun then the camera needs to be set to F32 to get a image that is right anything short of that is over exposing the camera and image. Or use a ND filter and knock it down to F4 or so to get a better image.

You have to understand how F Stops work or this will make not sense to you. The camera uses a mix of F stop, Shutter speed and ISO to expose the image right any of the 3 being set wrong will result in a image not exposed right you dont want to even shoot when the camera is not exposed right or with in a range of the exposure. Or you get the over exposed into the sun image. Not sure what the image flicker is but the image is way over exposed amazing the camera did what it did being that far over exposed.

You can expose part of a image like you are shooting a person talking and they are back lit you can expose the camera video to make the person talking be brighter and over expose the background on purpose to make the person talking pop out better so they are not so dark looking - photographers do that all the time to get shots it works the same way for video.

I shot on the beach every day shooting photography for many years all summer i had to deal with the super bright sun on every session. But with photography we can raise our shutter speed very high to knock down the sun to a manageable level when not using flash.

With video you can not do that or you run into shutter speed problems making the video look strobe effect so you need to use a ND filter to get that kind of bright sunlight shot.