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#11
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On Mon, 16 Aug 2004 22:52:30 +0200, Gary Whitehead
wrote: Hi Gary, As I mentioned in a previous post I've gone through many a thousand images so far. They ranged from Kodachrome (many versions with some as old as 50 years) Ektachrome, and a wide variety of 35mm negatives. It might help if you sort your slides by age, but you will find some pretty wide variations. Hi All, I wish to scan ~3-4000 slides, for two reasons, one to have the images available electronically but mainly to have a safe archive/backup of the images (most of these slides cover the period when I used to work for the British Antarctic Survey, are c20 years old and I would be gutted if I lost them...). I think the backup is a good idea, but if the slides were properly processed they will probably be around in good shape longer than the original digital media to which you save them. I've had a Nikon Coolscan 5000 ED for a couple of months, and have spent the time becoming familiar with it.... and colour management. On the colour I've been using the same since some where around Feb., or March. management issues I am now just starting to get a good overall idea of how things work (and I must admit it was not simple, and I am speaking as a lapsed physicist!). I would like to scan these slides ONCE - i.e. I would like to get it right the first time. I intend to scan at 48bits and 4000dpi (i.e. the max resolution of the scanner). At that resolution and depth the basic slide with no cropping will run about 126 to 130 megs. That comes out to about 520 Gigs of storage. or about 113 DVDs. I scan at 8 bits and haven't found any reason to go beyond that. The files are still roughly 60 megs as TIFFs. Can anyone comment on the scenario below: --------------------- * 16bits/channel / 4000dpi * Raw scanner RGB at - gamma 1.0 - (Nikon colour management turned off). * Only processing performed by the scanner being digital ICE My experience, using the SF210 automated slide feeder using digital ice only will be roughly 30 to 40 seconds per image. * Scanner calibrated using it8 targets and resultant icc profiles used to perform conversion to the working colour space (presently Wide Gamut RGB) on import of the raw gamma 1.0 files to Photoshop ---------------------- I am aware that there is a somewhat heated discussion on the subject of gamma 1.0 editing, which is not what I am proposing here. My concern is complete retention of the data delivered by the scanner. My reasoning is: * The scanner sensor has a 16bit resolution. * I acknowledge the sense in outputing a higher gamma file when using 8 bits/channel in order to space the resultant resolution perceptually. However when performing such a transform on the full bit data all I see is an increase in spacing of the scanner resolution at the shadow end at the cost of lost information in the highlights. I.e. I see no gain. * The scans are archival - I might wish to use the data in a couple of decades, with display technologies that may be completely different from Here lies a problem. To maintain data integrity you are going to have to refresh it at least once every ten years, or more frequently, as there is no real data to support storage life beyond that. Beyond a few years data lifetime is based on accelerated lifetime testing and projections. When archiving, the general approach is to make two copies and store them in separate locations that are friendly to the medium. (Dark, with temperature and humidity control) As you are not going to be using a rolling backup that rules out magnetic storage. Tapes and hard drives may have lifetimes of many years, but the lifetime to maintain data integrity is very short. Even with today's advances in hard drives which last 100s of thousands of hours you can not depend on that kind of life for the data. Typically HDs are refreshed on a monthly basis. I'd not want to trust one even in storage beyond a year. Optical on the other hand is potentially very long lived, but not proven. How long a particular medium remains viable (will the hard ware remain available to read and write said medium) and what media is practical for the amount of storage you need? Beyond 10 years there is the very real possibility of the need to change to a different media. Currently about the only thing I see that would meet the goal are DVDs and they come with no guarantee, only a projected lifetime. Unfortunately DVDs tend to vary in quality and can be susceptible to damage from handeling, which pretty much describes most optical disks. Store them on edge in Jewel cases and keep away from sun light. They should also be kept in a relatively low humidity and cool, but not cold temperatures. Check the manufacturers specs on storage. Above all, do not flex DVDs as most do when taking them out of the case. Press down in the center of the case and the DVD will pop out. Do not pull up on the edges. That will cause flexing and the DVD is a two layer device which can separate, or fracture. You are really on your own as far as quality control and how often you check them for data integrity. If you ever find a corrupt file you know you have waited too long. Hopefully the ones on the second backup will still be good, or at least the same files will not have failed. Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair) www.rogerhalstead.com today (i.e. why gamma encode the data with a value that derives from today's display technology). I would be particularly interested to hear from people in the high gamma camp(!), since I would guess from the gamma 1.0 camp I am going to hear "Go for it". The only potential problem that I can see here is whether the application of a gamma 2.2 curve through Photoshop/icc profile is any less accurate than in the scanner itself. I acknowledge that there may be others I have missed.... Cheers, Gary Whitehead. N.B. I too fought with the colour management on the scanner, and gave up in near disgust. Wolf Faust's targets, and resultant ICC profiles gave the best results I had seen within minutes of generating them! |
#12
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Roger Halstead wrote:
Here lies a problem. To maintain data integrity you are going to have to refresh it at least once every ten years, or more frequently, as there is no real data to support storage life beyond that. Beyond a few years data lifetime is based on accelerated lifetime testing and projections. When archiving, the general approach is to make two copies and store them in separate locations that are friendly to the medium. (Dark, with temperature and humidity control) As you are not going to be using a rolling backup that rules out magnetic storage. Tapes and hard drives may have lifetimes of many years, but the lifetime to maintain data integrity is very short. Even with today's advances in hard drives which last 100s of thousands of hours you can not depend on that kind of life for the data. Typically HDs are refreshed on a monthly basis. I'd not want to trust one even in storage beyond a year. Optical on the other hand is potentially very long lived, but not proven. How long a particular medium remains viable (will the hard ware remain available to read and write said medium) and what media is practical for the amount of storage you need? Beyond 10 years there is the very real possibility of the need to change to a different media. Currently about the only thing I see that would meet the goal are DVDs and they come with no guarantee, only a projected lifetime. Unfortunately DVDs tend to vary in quality and can be susceptible to damage from handeling, which pretty much describes most optical disks. Store them on edge in Jewel cases and keep away from sun light. They should also be kept in a relatively low humidity and cool, but not cold temperatures. Check the manufacturers specs on storage. Above all, do not flex DVDs as most do when taking them out of the case. Press down in the center of the case and the DVD will pop out. Do not pull up on the edges. That will cause flexing and the DVD is a two layer device which can separate, or fracture. You are really on your own as far as quality control and how often you check them for data integrity. If you ever find a corrupt file you know you have waited too long. Hopefully the ones on the second backup will still be good, or at least the same files will not have failed. Long term, I do not see too much of a problem in that relatively cheap devices that can hold the entire collection without raising a sweat are only around the corner - 300GB consumer drives are now available. Then I can easily manage redundant online storage. Short term I will have the set online on my server (for myself and my girlfriend I run a house (Linux) server, files, printing email etc), and rely on DAT tape for the offline backup. Basically, I can manage it now (with some hassle) and have redundancy, and wait in hope for the whatever cheap terabyte devices that are available in a couple of years. DAT tapes are advertised to have an archival lifetime in the range of at least a decade (and tape is a mature technolgy) which is much longer than I intend to rely on them for. They are also relatively cheap in cost/GB. |
#13
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CSM1 wrote:
Tape has the disadvantage of having to play the tape until you find the selection you are looking for. Also Tape is slow in transfer rate. Aye, but I plan to have them online as well (a couple of discs nowadays), the tape is for redundancy. However, I must admit that restoring the collection in the case of a disc failure would not be fun (c3hrs per tape). |
#14
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Greg wrote:
The *only* reason I don't use a gamma of 1 is that the profiler I use (the Little CMS scanner profiler) will only use 8-bit scans. If I feed the profiler higher bit depth target scans, the profiler definitely does not make use of the extra resolution. So, I use a gamma of 2.2 to get around this problem. I have been thinking about this and looking at my scans of the IT8 targets. I don't think that it actually matters much that we profile the scanners using 8 bit scans. Reasoning: 1. The scanned targets are actually quite noisy (film grain/target surface), giving in the midtones (using Photoshop's histogram tool) a standard deviation ~4-5bit (out of 256) on each channel, and maybe 1.5bits in the highlights, and 0.5bits in the shadows (for a single target square). Before anyone shouts at Wolf Faust, as I will explain below this is "Good Thing". 2. At 4000dpi we are averaging around 10000 samples for a colour square and maybe 40000 for a greyscale square. The resolution of the average can be approximated to the standard error which will be SD/SquareRoot(NoOfSamples). This gives me in the case of the midtones a standard error of around 1/25th of a bit for a colour square, which is almost an extra 5 bits of precision, i.e. around 13bits. No useful improvement would be seen by using a 16 bit scan. The other way of looking at it is that the quantisation noise of 8bit sampling (0.5bit) is insignificant compared to the target noise. (Errors should be added as a sum of squares). This is actually a standard technique in digital measurement, where it is recognised that the mixture of some noise (greater than the bit resolution) and averaging multiple samples allows sub bit resolution. The only area that I have some doubt on this argument is in the deep highlights (1-3 bits) and shadows. It is possible that there may be some clipping of the noise component which would tend to shift the average towards the midtones. I will take a look at a 16bit image later which I will range expand (i.e. expand levels 0-2 - 0-256). The test here is whether I see a normal distribution of points. If I do, then this should also be safe at the extremes. Of course this does all depend on the profiler perfoming its calculation in a sufficiently accurate data type and exporting the profiles in 16bits. Little CMS does appear to use the LUT16Type in its output, but I have not checked the code to see how it is calculated. |
#15
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Gary,
I have not digested your notes in detail yet, but, I do know that the version of the Little CMS profiler I am using definitely will *not* use anything greater than 8-bits per channel in the IT8 scans - I have even had this confirmed by the author himself. It will load the scan and process it, but it will not use the extra precision - it will discard it. Because of this, the author himself has said that it is very important *not* to use a gamma 1 scan - it is important to use a perceptually uniform gamma, such as 2.2. As you say, this issue is specific to the profiling software - other profilers which really can use the full precision would be entirelly suitable for use with gamma 1 IT8 target scans. Now, after saying all this, I am not sure whether there is a more recent version of the profiler available now - it's possible that this limitation has been removed. Greg. "Gary Whitehead" wrote in message ... Greg wrote: The *only* reason I don't use a gamma of 1 is that the profiler I use (the Little CMS scanner profiler) will only use 8-bit scans. If I feed the profiler higher bit depth target scans, the profiler definitely does not make use of the extra resolution. So, I use a gamma of 2.2 to get around this problem. I have been thinking about this and looking at my scans of the IT8 targets. I don't think that it actually matters much that we profile the scanners using 8 bit scans. Reasoning: 1. The scanned targets are actually quite noisy (film grain/target surface), giving in the midtones (using Photoshop's histogram tool) a standard deviation ~4-5bit (out of 256) on each channel, and maybe 1.5bits in the highlights, and 0.5bits in the shadows (for a single target square). Before anyone shouts at Wolf Faust, as I will explain below this is "Good Thing". 2. At 4000dpi we are averaging around 10000 samples for a colour square and maybe 40000 for a greyscale square. The resolution of the average can be approximated to the standard error which will be SD/SquareRoot(NoOfSamples). This gives me in the case of the midtones a standard error of around 1/25th of a bit for a colour square, which is almost an extra 5 bits of precision, i.e. around 13bits. No useful improvement would be seen by using a 16 bit scan. The other way of looking at it is that the quantisation noise of 8bit sampling (0.5bit) is insignificant compared to the target noise. (Errors should be added as a sum of squares). This is actually a standard technique in digital measurement, where it is recognised that the mixture of some noise (greater than the bit resolution) and averaging multiple samples allows sub bit resolution. The only area that I have some doubt on this argument is in the deep highlights (1-3 bits) and shadows. It is possible that there may be some clipping of the noise component which would tend to shift the average towards the midtones. I will take a look at a 16bit image later which I will range expand (i.e. expand levels 0-2 - 0-256). The test here is whether I see a normal distribution of points. If I do, then this should also be safe at the extremes. Of course this does all depend on the profiler perfoming its calculation in a sufficiently accurate data type and exporting the profiles in 16bits. Little CMS does appear to use the LUT16Type in its output, but I have not checked the code to see how it is calculated. |
#16
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On Wed, 18 Aug 2004 19:49:06 +0200, Gary Whitehead
wrote: Roger Halstead wrote: Here lies a problem. To maintain data integrity you are going to have to refresh it at least once every ten years, or more frequently, as there is no real data to support storage life beyond that. Beyond a few years data lifetime is based on accelerated lifetime testing and projections. snip Long term, I do not see too much of a problem in that relatively cheap devices that can hold the entire collection without raising a sweat are only around the corner - 300GB consumer drives are now available. Then I I hope to end up with a pair of 320s on each of three machines with a serial RAID on the 4th. That 4th machine is remote in another building. can easily manage redundant online storage. Currently I run redundant on line (mine) storage as do you. I have the work machine, one for backup and archive on DVD. I figure Hard drive data should be refreshed at least once a year if not more often. So far I've had good luck and it's quite fast across the 100 Mbps network. Short term I will have the set online on my server (for myself and my girlfriend I run a house (Linux) server, files, printing email etc), and rely on DAT tape for the offline backup. Basically, I can manage it now (with some hassle) and have redundancy, and wait in hope for the whatever cheap terabyte devices that are available in a couple of years. DAT tapes I have close to that now across my network at a relatively reasonable cost. Going to the 6 300 Gig plus drives and the serial RAID will not be trivial. They will make the 3 to 4 gig dual processor machine coming up look pretty reasonable. I run too much *stuff* and can bog down a single 2.8 gig processor. are advertised to have an archival lifetime in the range of at least a decade (and tape is a mature technolgy) which is much longer than I intend True, but with he advertised life of a decade I'd want to refresh at 5 years, which is only three refreshes over 20 years. to rely on them for. They are also relatively cheap in cost/GB. Good luck, It sounds like you have thought out your system well. Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair) www.rogerhalstead.com |
#17
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Gary,
I have checked with the author (Marti Maria), and there is in fact a new version of the scanner program, available he http://www.littlecms.com/profiler_qs.htm and this really does work with high resolution scans, and so in theory, gamma 1 should be safe. Marti cautions us that a) there is no support, and b) we should test it thoroughly with gamma 1 before relying on it too much, as gamma 1 still needs great care. If this is the version you're already using, then ignore my earlier warning. Greg. p.s I post this information with permission from Marti. |
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