Noise / dead pixels / low light, but....? (URSA MiniPro 4.6)

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Jim McQuaid

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Noise / dead pixels / low light, but....? (URSA MiniPro 4.6)

PostMon Jan 17, 2022 9:00 pm

I've owned the Ursa Mini Pro 4.6 for several years, using it primarily for work on short films and similar projects. In early January, I shot for two days and find that virtually every clip (100+) shows dead pixels.

I first noticed it in an "interrogation" scene - single bright light, rest of room in darkness. But then I realized these dead pixels (and the semi-subtle "striping" vertically through the image) appear in scenes with ordinary lighting (second attachment).

I've seen the "fixed pattern" noise occasionally before and generally avoid weak shadow areas and do the black level calibration semi-often when shooting.

So, has my sensor suffered a mortal wound (cosmic rays) or is there some elusive but significant aspect opf these scenes I am missing? I generally expose using the histogram, to the right if possible.
Attachments
detail - 928_C004.png
ordinary light...
detail - 928_C004.png (647.35 KiB) Viewed 882 times
detail - A929_C061.png
"interogation scene"
detail - A929_C061.png (676.55 KiB) Viewed 882 times
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John Brawley

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Re: Noise / dead pixels / low light, but....? (URSA MiniPro

PostMon Jan 17, 2022 11:27 pm

Over time, yes sensors DO COLLECT more dead pixels.

In theory when you boot the camera up, it's supposed to detect and turn off or hide those pixels.

BUT

sometimes if can loose that register of dead pixels, or maybe even be overflowing with the number. Things can co wrong and the dead pixels no longer are hidden and suddenly become visible.

You can try a power cycle in this circumstance, try to keep the camera very cool.

But once they are there, they are there forever. And another myth of digital sensors being better than film for longevity (of equipment) is killed :-)

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Jamie LeJeune

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Re: Noise / dead pixels / low light, but....? (URSA MiniPro

PostMon Jan 17, 2022 11:37 pm

Besides the dead pixels, there does seem to be an excessive amount of FPN in those shots.

Whether the FPN is an actual hardware issue depends on how the shots were taken and how the image was processed in post. It's impossible to diagnose simply from screenshots. What ISO was the camera set to when these were taken? And what transforms (if any) were applied in post? And how were the screenshots pulled?
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Uli Plank

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Re: Noise / dead pixels / low light, but....? (URSA MiniPro

PostTue Jan 18, 2022 1:38 am

He wrote: "rest of room in darkness". One of the typical mistakes in digital recording is starving the camera of light. Other than film, electronic cameras can't record black (or near black). You need to create enough contrast by proper lighting and pull-down the shadows in post.
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Howard Roll

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Re: Noise / dead pixels / low light, but....? (URSA MiniPro

PostTue Jan 18, 2022 3:38 am

Is the fan still working? The fpn is categorically horrendous.

Good Luck
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Jamie LeJeune

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Re: Noise / dead pixels / low light, but....? (URSA MiniPro

PostTue Jan 18, 2022 4:42 am

Howard Roll wrote:Is the fan still working? The fpn is categorically horrendous.
To me it looks more likely that the camera was simply underexposed while set to a high ISO and/or the image has been pushed in post before screenshot was taken.
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BennoZ

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Re: Noise / dead pixels / low light, but....? (URSA MiniPro

PostTue Jan 18, 2022 3:18 pm

There is a menu item in the 'Setup' tab named 'Calibrate sensor'. Hit that button and your 'dead pixels' are gone.
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Jim McQuaid

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Re: Noise / dead pixels / low light, but....? (URSA MiniPro

PostTue Jan 18, 2022 4:42 pm

Jamie LeJeune wrote:Besides the dead pixels, there does seem to be an excessive amount of FPN in those shots.

Whether the FPN is an actual hardware issue depends on how the shots were taken and how the image was processed in post. It's impossible to diagnose simply from screenshots. What ISO was the camera set to when these were taken? And what transforms (if any) were applied in post? And how were the screenshots pulled?


Definitely a lot of noise. The clips in question have not been processed at all. The screenshots were not done very scientifically but the degree of noise is a reasonable guide to how messed up the images are.
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Jim McQuaid

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Re: Noise / dead pixels / low light, but....? (URSA MiniPro

PostTue Jan 18, 2022 4:45 pm

Uli Plank wrote:He wrote: "rest of room in darkness". One of the typical mistakes in digital recording is starving the camera of light. Other than film, electronic cameras can't record black (or near black). You need to create enough contrast by proper lighting and pull-down the shadows in post.


But's here the question. In a situation where there is pool of very bright light and total darkness beyond, more than 12+ stops, shouldn't the darkness render as roughly 0 IRE? Otherwise a night shot of almost any kind is impossible.

Or put a different way, if the camera is presented with a "full scale" image (zones 1 thru 9) should the darkest tone render as "black" that is, textureless darkness?
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Jim McQuaid

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Re: Noise / dead pixels / low light, but....? (URSA MiniPro

PostTue Jan 18, 2022 4:46 pm

Howard Roll wrote:Is the fan still working? The fpn is categorically horrendous.

Good Luck


I would overheating to be the cause because I can fix that, but this distortion / noise is visible in the first shot of the day - in a huge unheated space!
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BennoZ

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Re: Noise / dead pixels / low light, but....? (URSA MiniPro

PostTue Jan 18, 2022 4:47 pm

This was definately shot with ISO higher than 800, otherwise your camera is broken.
The Ursa is very bad with low light situations in dark area's. You better expose higher and correct it in post. I shoot mostly ETTR which delivers very, very clean images.
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Jim McQuaid

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Re: Noise / dead pixels / low light, but....? (URSA MiniPro

PostTue Jan 18, 2022 4:51 pm

BennoZ wrote:There is a menu item in the 'Setup' tab named 'Calibrate sensor'. Hit that button and your 'dead pixels' are gone.


Unfortunately, I do that several times a day when I'm in an all-day shoot. However every clip has these artifacts, regardless. Alas.
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Jim McQuaid

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Re: Noise / dead pixels / low light, but....? (URSA MiniPro

PostTue Jan 18, 2022 4:55 pm

BennoZ wrote:This was definitely shot with ISO higher than 800, otherwise your camera is broken.
The Ursa is very bad with low light situations in dark area's. You better expose higher and correct it in post. I shoot mostly ETTR which delivers very, very clean images.


Both of the clips captured in the uploaded stills were exposed at ISO 800 according to MediaInfo. Both with a white balance around 3200. The "interrogation room" clip was shot with 360 degree shutter, the brown room at 180 degree shutter.
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Jim McQuaid

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Re: Noise / dead pixels / low light, but....? (URSA MiniPro

PostTue Jan 18, 2022 5:01 pm

Here's ONE of the issues. If the highlight detail in the frame is placed with the right exposure, say, histogram showing nothing brighter, and the surrounding area is below the end of the histogram, the darkness should render as darkness and there should not be any distortion in the highlight / middle tone areas.

If the important parts of the image were also underexposed (histogram empty on the right side), then FPN in the middle tones seems likely, especially at high ISOs.

What's really crazy is that it's proving hard to duplicate in order to test around this threshold.

My basic assumption is that ISO 3200 / 1600 are only usable in classic sunlight / bright / diffuse lighting (which is where you generally don't need it!)
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BennoZ

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Re: Noise / dead pixels / low light, but....? (URSA MiniPro

PostTue Jan 18, 2022 5:05 pm

Iso 1600 / 3200 is usable if you shoot f.i. for news items in the dark. Than you can deliver the recorded shots directly without any correction in post. I don't see any other usages for these high iso settings.
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Jim McQuaid

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Re: Noise / dead pixels / low light, but....? (URSA MiniPro

PostTue Jan 18, 2022 5:10 pm

Here's one more (partial) clip still from my misadventures with FPN. The actor is properly exposed and the darkness in the background renders as full black with no FPN. But the shadow side of the actor's face and parts of the shirt do show FPN in areas that are normally exposed, that is, histogram to the right, no highlights over-exposed.

Unfortunately making this small enough to upload hides some of the FPN artifacts. But they are still discernible.

The dead pixels DO appear in this clip however.
Attachments
929 - C005 on the gurney.png
Black renders as black - but FPN in properly exposed highlights / midtones
929 - C005 on the gurney.png (512.1 KiB) Viewed 524 times
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BennoZ

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Re: Noise / dead pixels / low light, but....? (URSA MiniPro

PostTue Jan 18, 2022 5:27 pm

Well this isn’t normal. Best option is to sent your Ursa for repair.
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Jim McQuaid

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Re: Noise / dead pixels / low light, but....? (URSA MiniPro

PostTue Jan 18, 2022 6:32 pm

BennoZ wrote:Well this isn’t normal. Best option is to sent your Ursa for repair.


I'm wondering about that option looming ahead. However, I'm first trying to figure out if it's a firmware corruption problem. The metadata field "com.blackmagic-design.camera.uuid" had a single (long / hex) value [918779f5-1d43-4537-b00c-9f1c5787949b] for the last several years worth of clips, then -- when I had this image problem - that field shows "unknown" and now it shows [cccccccc-cccc-ccc8-8888-888888888888].

Not certain I have the latest & greatest firmware (I'm running 6.0 in the camera) so investigating all of these things before sending the camera off.

It is definitely not normal!
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