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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 :)

Hot pixels

Miltos Pilalitos

Miltos Pilalitos

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I shot some night exteriors last night of traffic in the city. I set the varispeed to 1fps and took some very nice shots which unfortunately have very obvious hot pixels. They are even visible after i exported the shots from REDCINE to 720p DPXs

Are those hot pixels something to be expected at those framerates? Is it something that can be fixed in later builds?

Miltos
 
I assume by 1fps you were running the camera at an expanded exposure time - therefore nuked car headlights/street lights are to be expected at these exposures on any format - not just digital systems. Film would have the same issues although one or two stops more latitude isn't going to make an enormous difference at these exposures and general contrast ratios. HDRI gathering systems will make a difference but that tech is away down the pike a bit.

Short answer : once it blows, it goes.
 
I think Miltos is talking about individual pixels, not over-exposure or blown light sources. I've seen it here and there on a few timelapse shots I've done.

It's like the sensor needs a different black shading calibration for the longer exposure times. I'm wondering if setting the project and frame rate to the desired and then doing a black shading calibration would have any effect? Haven't tried it....
 
jtm said:
Its a pretty basic photography question -I assume by 1fps you were running the camera at an expanded exposure time - therefore nuked car headlights/street lights are to be expected at these exposures on any format - not just digital systems.
Click to expand...

I don't care about the nuked headlights/street lights. As you said those are to be expected and in my case also welcome.

What i am talking about is hot pixels. You see them where the background is dark, like the sky or a dark wall or black subjects. Hot pixels might be blue, pink white or other crazy colors.. You know... Hot Pixels.
 
Jeff Kilgroe said:
I think Miltos is talking about individual pixels, not over-exposure or blown light sources.
Click to expand...

Yeap... that's right.

Jeff Kilgroe said:
It's like the sensor needs a different black shading calibration for the longer exposure times. I'm wondering if setting the project and frame rate to the desired and then doing a black shading calibration would have any effect? Haven't tried it....
Click to expand...

I haven't tried that either. If i remember well it makes a difference only if you change the ASA setting but yesterday i had ASA at 320 so i am not sure if it would make a difference.

Thinking about it... Would it be ok if we set ASA at something extreme like 2000 and then do the black shading? Would that affect footage shot at normal ASA settings afterwards?
 
Strange that 1fps would bring out hot pixels, but regular 24/30/120p shooting does not.

Maybe try bringing them into AE? I regularly shoot 45-second exposure RAW timelapse sequences on my DSLR (i have about 5 notorious hot pixels) and AE always seems to remove the hot pixels in the Camera Raw stage, without me doing anything. I'm not sure if it would do it for TIFFs or DNGs or whatever.
 
I'm pretty sure I remember someone from RED mentioning that when you go to timelapse or very slow varispeed stuff you need to do another black shading, I think that should help.

Let us know.
 
jtm said:
Have you got a frame grab of these Hot pixels?
Click to expand...

When i exported a frame out from REDCINE they seem to be somehow less obvious. (?)

Anyway... Here is an example:

Z000006-A003_C003_0927NQ_0285.jpg


jtm said:
Is that every single time you switch to those speeds?
Click to expand...

Yeap... Same position too! :-)

No doubt they are hotpixels.
 
It is stated from red that standard practice is to set your varispeed (for time-laps) and then do a black shading. Have you tried that? i haven't heard of anybody doing that and having the hot pixel issue.
 
After setting the varispeed to 1fps i didn't do a black shading. I knew about doing it after high ASA settings but never heard about low FPS settings.

Do you remember where it was discussed? i might need to do some reading.

Miltos
 
Do another black shading for such long exposure times.
And don't forget to repeat the process when going back to regular speed.
 
Yes, at extremely long exposures, ( I believe 1/2 sec or longer) you need to re-black shade once in said mode.
Don't forget to do it again when you come back out.

cheers
 
Hy Miltos,

I'm wondering if your problem can be compared to dead pixel on CCD sensors, very common en Canon XLH1 for exemple.

Every CCD has dead pixel but once you fill your camera memory with a whole bunch of dead pixels, the system is unable to hide them anymore. I had to change 2 camera XLH1 bodies for that exact reason.

To see the dead pixels on the CCD camera I push the gain to the maximum (+12, +18) and look at a black picture on a big screen. They just pop on your face. This could also happen (?) with Red on higher ASA or slower shutter speed as you demonstrated...

I don't know the implications of dead pixels on a CMO as there will be a debayer applied on the dead pixel and the sum of 1 pixel value is created by surronding pixels.

I find it concerning that the sensor could have dead pixels problems and therefore I kindly ask you to make some more tests (black shading...) and give your results on this thread. :-)

Thanks a lot.

Patrick
 
If it were a dead pixel issue, it would show up under all circumstances. Do the recommended Black-cal and you should be fine. As mentioned, remember to do it again when you come out of that mode.

Jim
 
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