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Photo Forum / Digital Photography / DSLR Cameras / December 2005Is compact flash airport-safe?
Sorry if this question has already been addressed here but I did not find anything on a search of this NG. Is CF resistant to xrays used in airport screening machines or can the images be degraded or erased going through airport terminals? I figure they must be safe or I would have heard about it but we are going on a vacation in the next few months and I need to be sure. Thanks, Tien ttda...@hotmail.com wrote: > Sorry if this question has already been addressed here but I did not > find anything on a search of this NG. Either you are lying or you are incompetent. Try this search: http://groups.google.com: compact flash airport xray Oodles and oodles of hits, going back years and years. > Sorry if this question has already been addressed here but I did not > find anything on a search of this NG. [quoted text clipped - 7 lines] > > Tien I've had no problems with CF or SD cards as hand luggage. Never had them as checked-in baggage. David In theory yes - and in practice yes too - (I would think the vast majority of the time). My only hesitation was when I took a digital diary overseas with me once - until that time it had literally never missed a beat - and as soon as I went to use it overseas it had a corrupted database. Obviously something had flipped a few ones and zeros somewhere along the way. Is it an option to keep it/them in your shirt pocket and get a visual inspection? As I say, probably not necessary, but considering how small they are, it's probably a non-issue to get them manually inspected also. > Is CF resistant to xrays used in airport screening machines or can the > images be degraded or erased going through airport terminals? I figure > they must be safe or I would have heard about it but we are going on a > vacation in the next few months and I need to be sure. I was on a 10 day cruise where everything was x-rayed, scanned etc every time we returned to the ship. We also experienced this at our airport destinations. My CF cards experienced this for the whole trip. All 600+ images were intact. In my experience, I had no problems at all. > > Is CF resistant to xrays used in airport screening machines or can the > > images be degraded or erased going through airport terminals? I figure [quoted text clipped - 5 lines] > destinations. My CF cards experienced this for the whole trip. All 600+ > images were intact. In my experience, I had no problems at all. Same here. 729 images on 7 CF cards. Every picture is fine. Even if there was damage, it would typically be limited to a single bit, and therefore a single pixel. One pixel on one image - can hardly call that damage worth worrying about. Austin > Even if there was damage, it would typically be limited to a single > bit, and therefore a single pixel. [quoted text clipped - 3 lines] > > Austin Although a single bit wrong in a JPEG file could stop you reading the whole file, and possibly a single bit wrong in the file system could stop you reading the whole card. David > > Even if there was damage, it would typically be limited to a single > > bit, and therefore a single pixel. [quoted text clipped - 7 lines] > whole file, and possibly a single bit wrong in the file system could stop > you reading the whole card. I don't know about jpg's, you may be right. But as a programmer, I would be stunned if a single bit could bring down a file system. Even MS-DOS's file system (FAT16 ? - don't remember), a truly primitive one using over 20 year old technology, required more than 11 bad bits before a sector could not be corrected. If the 11+ bad bits were in a FAT sector, it could still be recovered (though not by DOS - DOS could create the second FAT, but then proceeded to ignore it, requiring a 3rd party utility to fix it with no difficulty). Believing a file system that today typically stores 100 to 500 times as much as my first hard drive without built-in error correction is simply beyond me. Austin > I don't know about jpg's, you may be right. The business about one bit sh.tting an entire file is a very low probability event -- there isn't much metadata in a JPEG or even RAW file, and not much of that is super-critical to the point that one bit prevents decoding. An SEU mid-stream can cause the decoder to lose sync, resulting in crud thereafter. You can hexedit a few JPEG's to see what happens. (For a color JPEG, there are three encoded chunks, and an SEU in one chunk only effects that chunk, though the visible result is from that point in the image on to the end.) > But as a programmer, I would be stunned if a single bit could bring > down a file system. Even MS-DOS's file system (FAT16 ? - don't [quoted text clipped - 4 lines] > proceeded to ignore it, requiring a 3rd party utility to fix it with no > difficulty). Modern filesystems are indeed more robust than people around here think: a single bit error just won't be able to render an FS unusable or unfixable. The main problem is the physical destruction of the information substrate. And no carry-on xray machine will come close to doing this to a flash memory device. > Believing a file system that today typically stores 100 to 500 times as > much as my first hard drive without built-in error correction is simply > beyond me. Maybe Mythbusters accepts submissions? Wouldn't make for an exciting episode though, rolling CF or SD cards through an xray machine or twiddling bits in filesystems. Mind you, though, they did do one about mag-stripes being erased by "eel skin wallets" (the sh.t people believe!). Long segment with Adam sitting there trying his best to destroy a mag-stripe on some cards. In the end they gad to build, in effect, a powerful degausser. What would they make for a CF destroyer? [] > The business about one bit sh.tting an entire file is a very low > probability event -- there isn't much metadata in a JPEG or even RAW [quoted text clipped - 6 lines] > chunk only effects that chunk, though the visible result is from that > point in the image on to the end.) Yes, I've seen exactly that effect, although on a JPEG which had been sent over a radio link. > Modern filesystems are indeed more robust than people around here > think: a single bit error just won't be able to render an FS unusable > or unfixable. The main problem is the physical destruction of the > information substrate. And no carry-on xray machine will come close > to doing this to a flash memory device. .. and FAT-16 is a modern file system? Having said that, I haven't seen any problems with taking CF or SD cards through hand-baggage inspections, and would have no hesitation in so doing. David > a powerful degausser. What would they make for a CF destroyer? My guess would be your "powerful degausser". There's a big difference between X-ray and a magnetic field. I suspect a powerful magnet would nuke a CF card. :) JR >>> Even if there was damage, it would typically be limited to a single >>> bit, and therefore a single pixel. [quoted text clipped - 24 lines] > > Austin The error correction is there, built into the hard disk itself. Yes, modern file systems try harder to prevent data loss in critical regions from damaging the file system, but we all know it can and does happen. As the memory card is typically used as a data-only card, some single-bit errors might not stop it being read by a third-party utility, as you say. Some errors in the boot block code, for example, would not matter. What about any master partition table? And recall that I said "possibly". David > Even if there was damage, it would typically be limited to a single > bit, and therefore a single pixel. > One pixel on one image - can hardly call that damage worth worrying > about. Sorry, due to compression (lossy with jpeg, lossless with RAW) this is not the case. You can easily loose the whole image. Or the file system, as has been mentioned. -Wolfgang >> Even if there was damage, it would typically be limited to a single >> bit, and therefore a single pixel. [quoted text clipped - 9 lines] > > -Wolfgang CompactFlash cards have built in error Correction (ECC). A one bit error would be corrected so that the file system or a file read from the card would have no errors. Bill Frank CompactFlash Association >>> Even if there was damage, it would typically be limited to a single >>> bit, and therefore a single pixel. [quoted text clipped - 16 lines] > Bill Frank > CompactFlash Association Is that mandatory for all cards, or might some of the cheaper ones omit ECC? The link below appears to include CF cards both with and without ECC: http://www.globalsources.com/manufacturers/Compact-Flash-Card.html David >>>> Even if there was damage, it would typically be limited to a single >>>> bit, and therefore a single pixel. [quoted text clipped - 24 lines] > > David I don't see any listed that say they are without ECC. A couple say they have ECC. That's kind of like saying that a specific CF card operates at 3.3V and 5V vs. not mentioning it. They all can operate at either voltage. I am not aware of any CF card that does not have ECC since it is included in all brands of controllers. Bill Frank CompactFlash Association > "David J Taylor" > <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk.invalid> [quoted text clipped - 38 lines] > Bill Frank > CompactFlash Association Point taken, but it is misleading if some say they have ECC and others don't! Glad to hear it's in the controllers - very reassuring. I've been pleased with the reliability of both CF and SD storage for my digital cameras, although I now prefer SD as it seems to have a better contact mechanism. (Oh, I hope that's not out of order! <G>). Cheers, David > "Wolfgang Weisselberg" <ozcvgtt02@sneakemail.com> wrote in message >>> Even if there was damage, it would typically be limited to a single >>> bit, and therefore a single pixel. >> Sorry, due to compression (lossy with jpeg, lossless with >> RAW) this is not the case. You can easily loose the whole >> image. > CompactFlash cards have built in error Correction (ECC). Thanks for pointing that out! > A one bit error would be corrected so that the file system or a file > read from the card would have no errors. Even more than a single bad bit should be corrected without the user noticing, I guess. But, if there _was_ a user visible error (i.e. too many errors than the ECC can handle) it'd not be just a few pixels in a JPEG. -Wolfgang Just went thru this (with a microdrive) and no problems. I took a couple of junk pics before going and checked them after going thru the xray to decide if I'd allow it with my vacation pics on the return...no problems either way (I couldn't really think of a reason for a problem either). George > Sorry if this question has already been addressed here but I did not > find anything on a search of this NG. [quoted text clipped - 7 lines] > > Tien > Sorry if this question has already been addressed here but I did not > find anything on a search of this NG. [quoted text clipped - 7 lines] > > Tien Yes, it's completely safe. 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