Corrupted JPEGs on Mac

[pgk]

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I have been writing DVDs of images for a client and have run into an odd problem. The DVDs contain a mix of RAW and JPEG files in different folders. The RAW files write fine but all the JPEGs are corrupted - the lower halfish of the image is grey, which appears to be a write problem with the DVD writer. I am satisfied that this is the probably cause however two things baffle me. Firstly the RAWs write ok and are bigger files. Why? And secondly and more worryingly, the JPEG files on my computer are also corrupted in the same way. As I checked them prior to writing the DVDs I'm sure that they were ok and its the burning of the DVDs which has corrupted them. Does anyone have any ideas about this? (I had a memory error message from the  firewire DVD writer once during multiple DVD writing if that helps? Writing the DVDs again with a different usb DVD writer has solved the problem.

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[zeitz]

Paul, this sounds like incredibility bad fortune.  Can you provide us the technical details of your situation - Mac model, OS version, RAM, raw format, optical drive model, graphics card, etc?  Are jpegs that you did not try to copy still readable correctly?  Is the date/time of the affected files the original or is date/time updated from the time you burned the DVD?  Are you using a DVD writer other than what is in Finder?  When is the last time the DVD writer worked correctly?

[dau]

Bad luck, indeed.

I presume that there's a simple explanation for the raw files remaining intact while the jpegs were corrupted. It seems that no copression is being applied to the raw files while the jpegs are compressed, Dropping a few bits in an uncompressed raw files most likely produces a few faulty dots in the file, similar to hot pixels as produced by the sensor. Dropping a few bits in a compressed file may render everything unreadable that follows the error in the file.

Unless the program which writes to the DVD has some very unusual features indeed, there's no way it can corrupt the files on the disk it is supposed to copy to the DVD. I would presume that the fault lies within the Mac which all of a sudden failed reading the files off the disk. The files then were written to the DVD exactly as they were read from the disk, i.e. with some damaged areas, possibly very small ones.

The wording of the error message you mentioned above might be useful.

In any event, I think you can not trust your Mac anymore to properly keep or read your files. Thinking about backup copies of your images should be on the top of your to do list.

Edited December 9, 2018 by DAU

[pico]

49 minutes ago, DAU said:

In any event, I think you can not trust your Mac anymore to properly keep or read your files.

I must disagree. If the problem is only with JPEG files, something is wrong, certainly, but not with the Mac in general.

 

[dau]

vor 1 Stunde schrieb pico:

I must disagree. If the problem is only with JPEG files, something is wrong, certainly, but not with the Mac in general.

 

I don't quite believe the problem is with JPEG files only. Rather, I think spotting the problem in an uncompressed raw image file would be quite difficult as most likely it would affect a few pixels only. On the other hand, altering a few bits in the middle of a compressed stream would ruin the decompression for whatever follows the error in the file.

However, we won't be able to find out if that is really the case without actually seeing any affected files.

[pico]

1 hour ago, DAU said:

I don't quite believe the problem is with JPEG files only. Rather, I think spotting the problem in an uncompressed raw image file would be quite difficult as most likely it would affect a few pixels only. On the other hand, altering a few bits in the middle of a compressed stream would ruin the decompression for whatever follows the error in the file.

However, we won't be able to find out if that is really the case without actually seeing any affected files.

I think you are poorly informed, just plain wrong if you place the blame on the OS.

[dau]

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8 hours ago, pico said:

I think you are poorly informed, just plain wrong if you place the blame on the OS.

I don't think anything I've written so far implies the OS. As a matter of fact, no one here knows enough about the issue to identify the component or components which cause it.

[pico]

1 hour ago, DAU said:

I don't think anything I've written so far implies the OS.

Quote

I would presume that the fault lies within the Mac which all of a sudden failed reading the files off the disk.

I think you can not trust your Mac anymore to properly keep or read your files.

Nuff said regarding your impressionistic diagnosis.

Edited December 10, 2018 by pico

[dau]

vor 6 Stunden schrieb pico:

Nuff said regarding your impressionistic diagnosis.

Well, yes. The Mac is a box containing many hardware parts and many software components. Paul states that all of a sudden the box fails to produce exact copies of some files he has stored in the box. I certainly would worry about all files at least on the same drive and I would hurry checking the backup copies. 

[pgk]

Well, I've regenerated the JPEGs and rewritten the DVDs using a different DVD writer and all appears to be fine. So I'm assuming that the DVD writer was at fault. I'm still baffled about theJPEGs on my hard drive (SSD) though because I am pretty certain that the writing to the dodgy DVD writer was the cause of this as they were ok before I did so. So I'm still baffled by what happened but I do have a working solution as well as a junk DVD writer.

I am using a MacBookPro; the DVD writer at fault was a LaCie external unit - oldish but no problems with it up until now - but was firewire so was running through an adapter. I did get one failed DVD and an memory error message when this happened but of course I assumed a bad DVD and ignored it! 

[zeitz]

Paul, what macOS are you using?  Your version of LaCie may not be compatible with newer macOS versions.

[pico]

58 minutes ago, zeitz said:

Paul, what macOS are you using?  Your version of LaCie may not be compatible with newer macOS versions.

I would be amazed if that were true. DVD protocols are quite well settled.

 

[zeitz]

Optical drives use drivers, just like any device, that can be generic in the OS or specific for a particular optical drive.  Drivers routinely stop working when major changes are made to an OS.  Apple in particular has tried to eliminate optical drives from its Macs.  The fact that Paul tells us he uses a LaCie optical drive tells us he has a newer MacBook Pro because it does not built-in optical drive.  And the fact that the LaCie has a Firewire connector tells us that the LaCie is old because Apple abandoned Firewire years ago.  PCs never really embraced Firewire; I assume expansion cards are still available to add Firewire to PC desktop computers.

[pico]

17 minutes ago, zeitz said:

Optical drives use drivers, just like any device, that can be generic in the OS or specific for a particular optical drive.  Drivers routinely stop working when major changes are made to an OS.  Apple in particular has tried to eliminate optical drives from its Macs.  The fact that Paul tells us he uses a LaCie optical drive tells us he has a newer MacBook Pro because it does not built-in optical drive.  And the fact that the LaCie has a Firewire connector tells us that the LaCie is old because Apple abandoned Firewire years ago.  PCs never really embraced Firewire; I assume expansion cards are still available to add Firewire to PC desktop computers.

 

Drivers? You might be a WinDoze person. Your logic is some kind of popular impressionist silliness. Macs today accommodate all DVD and SD protocols. We disagree on too many points to continue. Give it up.

Edited December 10, 2018 by pico

[pgk]

Well, it is an old LaCie and its certainly the common denominator in that its the only thing I've changed and changing it has solved the problem. But I'm still baffled that the JPEGs on my MBP SSD were corrupted. This is what puzzles me most. I'm wondering if a virtual 'disk image' is formed in RAM when using the burn function and somehow this has written the corrupted files back to the SSD? But if so why/how?

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