My camera ( Pentax K-x ) creates DNG files which contain two preview jpeg images. One rather small ( 640x480 ) and a full-size ( 4288x2848 ) image. The second one increases the DNG size by 10%.

Should I remove the preview image to decrease the size of the file, or is it worth to keep the preview image? What is the advantage of the full-size jpeg preview image?


The preview image tends to be used as a thumbnail in the computer, it can be used to quickly glance at a bunch of files and figure out which is the one you want. It's up to you, but I recommend keeping the preview image. It doesn't need to be full sized, but the small image should be worth it.

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    As a sysadmin, I have to disagree. Cheap disk is cheap. Storage for data you want to preserve is expense. – Please Read My Profile Dec 31 '10 at 15:09
  • @mattdm - For the home user you can get several external terabyte+ sized drives for backup purposes for very little money. I have three and seriously doubt all 3 are going to fail at the same time and/or in the same sectors. That's sufficient I think and probably a heck of a lot more than the vast majority are doing. In any case, even in the interprise, disk is still cheap if you compare storage growth versus cost. – John Cavan Dec 31 '10 at 19:09
  • Do you have an automated process which transfers data between these three drives? What keeps an error from being propagated? Do you periodically validate the data? What if your house is struck by lightning and it overwhelms your surge protection? What if your home burns down? – Please Read My Profile Dec 31 '10 at 19:52
  • @mattdm - If my house burns down, I'll have bigger things to worry about. Seriously, what's with the bee in the bonnet? The average user here is not a major company and are not going to spend millions on massive redundancy and off-site storage facilities with fireproofing. Multiple backups to low cost external drives is more than reasonable and not expensive. Do you really think it's so expense that somebody needs to squeeze out a few megabytes from an image? Cost per megabyte of disk is peanuts even for more protective home solutions. – John Cavan Dec 31 '10 at 20:19
  • I dunno if it's a "bee in the bonnet" -- that's a weirdly antagonistic turn of phrase. Perhaps you have some insects in your own headgear, here? There's some weird conflicts in your comment here: on the one hand, you suggest that a made-up "spend millions", and then say that a cheap solution is "more than reasonable". The real answer for a serious and conscientious home user is somewhere in-between, and for many reasonable in-between solutions, a 10% decrease in long-term storage size of redundant data might in fact be easy savings. – Please Read My Profile Dec 31 '10 at 20:32

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