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Artifacts on Alexa

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Dinis Rodrigues
Artifacts on Alexa
on Feb 7, 2014 at 3:31:39 pm



Got this when viewing on a pc or mac, these random artifacts all over the image.
Shot on Alexa 2k 444. All the clips got this, 6 different cards, interior shot.
The clips were viewed from the hard drive the cards were copied to, a 2TB WD drive.

Haven't had a change to retest the camera, but does anyone have any idea what it might be?


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David Battistella
Re: Artifacts on Alexa
on Feb 7, 2014 at 4:45:00 pm

Ouch,

Is this across all of the copies? How were the cards copied? Did they do a visual verify on set?

I'd get your rental company on this right away.

I'm sorry this happened. This is why the copies are important but so is the visual verification to catch this stuff as it is happening.

Stuff like this can even be caused by a bad cable between the reader and the computer.

Battistella

______________________________

http://www.bottegabattistella.com/blog/


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Dinis Rodrigues
Re: Artifacts on Alexa
on Feb 8, 2014 at 4:44:43 am

Thanks for the reply.
I have no idea how it happened, but I see now that the audio got the same problem, so it's gotta be the hard drive. We previewed a couple seconds here and there, same with the audio, no problems then. Something must have happened after the shooting up to the beginning of the editing for all the files to have that kind of damage, just no idea what.


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gary adcock
Re: Artifacts on Alexa
on Feb 7, 2014 at 5:09:39 pm

[Dinis Rodrigues] "Shot on Alexa 2k 444. All the clips got this, 6 different cards, interior shot.
The clips were viewed from the hard drive the cards were copied to, a 2TB WD drive.
"


OK.
First off this is not any type of error that would happen in-camera, Alexa Sensor errors tend to have multi-colored pixilation due to the nature of the CMOS sensor. The camera would also be indicating is something this drastic had happened.

You also do not mention what format the content is which 2K frame size, and what frame rate.
Did you record to SxS ProRes 444 or ArriRaw 444 ?

SO.

What app's are you viewing the file in?
Are you viewing them all from the same media on both computers?
How are the drives formatted?

Have you checked a backup copy of the media? Having this on 6 different pieces of media makes me think that the error is on the harddrive holding the content and not in the camera originals.

gary adcock
Studio37

Post and Production Workflow Consultant
Production and Post Stereographer
Chicago, IL


Follow my blog at http://www.garyadcock.com

Or follow me on Twitter
@garyadcock




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Dinis Rodrigues
Re: Artifacts on Alexa
on Feb 8, 2014 at 4:53:54 am

Hi Gary.
It was on SXS.
The transfer was done with a thunderbolt cardreader to a usb docked drive.
Being low budget and short-staffed, there was no backup.
After checking the same kind of errors on recorded sound, it seems to be the hard drive.
There was a couple short checks here and there, and the size of the card was checked with the size on disk after every transfer.
The files were seen on a mac, both vlc and quicktime, then one of them was sprended to me, seen on pc (quicktime and premiere).

As the cards seem to playback fine on camera, I'm left believing there was damaging throughout the harddrive. It just doesn't make sense how, as mechanical-wise, the hard drive seems to function fine. It's like something was copied over the hard drive space, over the files, but how does that happen...?
The harddrive is formatted as exFAT by the way.


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gary adcock
Re: Artifacts on Alexa
on Feb 8, 2014 at 6:53:30 pm

[Dinis Rodrigues] "It just doesn't make sense how, as mechanical-wise, the hard drive seems to function fine."

Drop outs. those are small individual partitions on the drive.

Have you tried coping the data to some other media?

gary adcock
Studio37

Post and Production Workflow Consultant
Production and Post Stereographer
Chicago, IL


Follow my blog at http://www.garyadcock.com

Or follow me on Twitter
@garyadcock




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Dinis Rodrigues
Re: Artifacts on Alexa
on Feb 9, 2014 at 12:59:05 am

Yes. I mean, not me, the hard drive is on the post-house at the moment. I'm getting it and testing it on monday.
They were the ones finding out that across all the videoclips there is the same problem.
It's possible to copy the file to other media, which is strange. The image uploaded here was a picture from a file that was sent to me by sprend, so technicaly they were able to upload it on internet and I was able to download it.

All the problems I ever had with dying/damaged harddrives were either physical problems where you can ear it and can't even read/copy the whole file or corruption on the mbr part which can be recreated and the files recovered.
I'm not hard drive expert, of course, but this seems like something was written over on some sectors. I'm thinking about, on monday, copying a healthy large file to the hard drive and then copying it back and play it, to check if it's the hard drive fault or if something happened after I gave away the hard drive. Do you have any other suggestions, as I didn't know a thing like this could happen?
Could it be a virus or a sort of magnet that touched the drive?

I also found out today that when the alexa formats a card (not "erase card"), even though it takes just a couple seconds, it is a destructive format, unlike when you format a normal harddrive or card through the operative system. It seems that the Alexa also randomly writes all around the card to make it impossible to undelete/unformat it.


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gary adcock
Re: Artifacts on Alexa
on Feb 9, 2014 at 1:58:15 pm

[Dinis Rodrigues] "
I also found out today that when the alexa formats a card (not "erase card"), even though it takes just a couple seconds, it is a destructive format, unlike when you format a normal harddrive or card through the operative system"


First- I am regularly able to recover media from re-formatted Alexa SxS cards in a reliable fashion so that is not your issue. THIS IS NOT A CAMERA ISSUE

Again. I am more than sure the error you see is failure of the storage media chosen to store the Camera data on, not in the media or the transfer from SxS.

Those lines appear to be from the individual block sectors failing failing on the drive itself - and since EXFAT does not allow for error correction compensation on media, the drive mechanism does not know not to write on the bad segments of the media

There is no excuse for not making a backup copy when handling data, it's somewhat akin to handling film in the light-DONT DO IT.

gary adcock
Studio37

Post and Production Workflow Consultant
Production and Post Stereographer
Chicago, IL


Follow my blog at http://www.garyadcock.com

Or follow me on Twitter
@garyadcock




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Dinis Rodrigues
Re: Artifacts on Alexa
on Feb 9, 2014 at 2:51:56 pm

Hi Gary

Thanks for the great insight.
I wasn't aware of that flaw on exFAT hard drives. I also completely agree with you on the backup issue, and me and the DP tend to warn of those risks to the production, but sometimes they underestimate it.
Those individual block failures must also have happened post copying, as we would have detected them while copying during those couple seconds of playback.
I guess now we have a story to tell next time they insist on no backup.

Also, do you know how to recover footage from cards formatted on camera?
I tried like 5 different recovering pieces of software, they all came empty, even on the longer methods. The formatted card is named ARRI_UDF, which is normal with all formatted cards and was formatted with the "format card" quicker method.


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Dinis Rodrigues
Re: Artifacts on Alexa
on Feb 10, 2014 at 1:51:35 pm

Problem solved :)

A bit unexpected but makes sense.
It was the harddrive dock.
All the files were copied fine but, when they are read now, they are passing misinformation, giving origin to those artifacts. Changed dock and all the material was there and fine.

Thanx for your help and great insight.


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gary adcock
Re: Artifacts on Alexa
on Feb 10, 2014 at 2:33:18 pm

[Dinis Rodrigues] "Those individual block failures must also have happened post copying, as we would have detected them while copying during those couple seconds of playback."

Why? its not like you can see what is going on while the file is writing. You are writing Gigabytes there is no way you would see a bite error that small- thats why you write data with verification by MD5 or CRC32 checksum tests.


"Also, do you know how to recover footage from cards formatted on camera?"

Most Formatting only destroys the header/ directory on the media, the data is not damaged in most cases, and ARRI uses the same UDF formatting that Sony does for that media the process is not that difficult.

I will say that some of the tools are off the shelf and some are not.

gary adcock
Studio37

Post and Production Workflow Consultant
Production and Post Stereographer
Chicago, IL


Follow my blog at http://www.garyadcock.com

Or follow me on Twitter
@garyadcock




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Gaetan Charest
SXS Card formatted by accident
on May 19, 2014 at 7:18:39 pm

A SXS chip has been reformatted by accident in a sony PWM 200. As soon as the formatting was completed we pull the chip out of the camera.

WE need to recover the material (priceless) from the SXS card which is formatted UDF. is there any chance to recover?


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gary adcock
Re: SXS Card formatted by accident
on May 20, 2014 at 12:02:55 am

[Gaetan Charest] "WE need to recover the material (priceless) from the SXS card which is formatted UDF. is there any chance to recover?"

If there is only a single take on the card, it is lost, if there are multiple takes, there is a good chance the data can be recovered.

It is not simple nor is it inexpensive, did you talk to the people that rented you the camera? That would be the first place to start.

gary adcock
Studio37

Post and Production Workflow Consultant
Production and Post Stereographer
Chicago, IL


Follow my blog at http://www.garyadcock.com

Or follow me on Twitter
@garyadcock




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Gaetan Charest
Re: SXS Card formatted by accident
on May 20, 2014 at 2:21:59 am

We own our camera, So we don't have anywhere to go. Good news--if any--we have multiple shots on the chip maybe 20 or more.


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