Wow, this article has got a lot of trtciaon, and (unfortunately) a little misinformation (not a lot, but )First, on backup: a hard drive (in time machine or anything else) is NOT a backup. It is a copy, an offline copy (probably), and that is A Good Thing, but if one is concerned about optical media as a backup format, one should run screaming from any hard disk. The reason for this is that for backup you have be concerned about all sorts of failure modes, including the often overlooked how will you read the thing in 10 years? one (suppose you’d used SCSI disks as a backup media a decade ago now what?). For an HDD (hard disk drive), you need to worry not only about media faults (not being able to read a particular chunk of media) but also motor/bearing/interface failures, which render the whole thing about as much use as a brick. But even worse, because HDDs have critical moving parts, they also need lubrication in order to work . and that lubrication will evaporate over time. So eventually a disk sitting on a shelf will become a brick, and the only way you’ll get your data back is by spending a lot of money with a disk recovery business, and crossing your fingers.Optical media is preferable as long as the dyes in the media is archival grade and they are store properly but the main reason to prefer it is that the media is cheaper (although the time to burn it isn’t, so that must be considered). Because the media is cheaper, the thinking goes, you’re more likely to have multiple copies, and because it is light and relatively robust, you’re more likely to have remote copies, too.The best media for backup is tape (still). Unfortunately, a sound backup strategy needs *2* tape drives (one to write, the other to verify), otherwise you risk creating backups that only one drive in the world can read and that drive will be the one that just went up in smoke. The good news is that cloud backup services usually include tape-based backup of the storage, so this is (yet another) reason to go that route.By the way, if you do have a RAID drive fail, the best thing to do is to keep the whole thing running and use it as little as possible; don’t power it, or the attached computer, off until the new drive is installed (or ready to be installed if you don’t have hot plug), because a huge area of complexity for RAID controllers is figuring out which drives to use if, for instance, the formerly dead disk gets better . They should get it right, but it’s your data, not theirs, that will be corrupted if they don’t Even more by the way: RAID1 is always a better choice than RAID5, except for the pesky issue of cost and connectivity. So six disks arranged as 3 RAID1 pairs is better than four disks as one RAID5 set, given that we’re all made of money! (Oh, wait ).Second, others have pointed out the fallacy of worrying about lossless compression. Certainly, if you save anything to a cloud, your data is going to be (losslessly) compressed anyway, so this is a non-issue.Third, the comments about vector formats being supported by TIFF are (at least partially) valid, but entirely irrelevant to a discussion about scanning. Sure, if you want a single file format for multiple types of image, then this is a very reasonable concern, but for scanning, you’re not going to be getting vector formats.Fourth, Adobe’s DNG is equally irrelevant to scanning, because DNG is a format designed to be a superset of camera sensor raw formats, and a lot of value of raw sensor data is that things like white balance and exposure can be tweaked. A good scanner will control those (the lamp produces the same color light, for example), so DNG doesn’t really have a role to play here.Fifth, as has been suggested above, the Achilles Heal of TIFF is that it is not fully standardized (the spec is actually copyrighted by Adobe), and (to make it worse) it is a Container type format (like AVI or MOV for video). So a TIFF file can have the image data in one of many formats, including lossy compression (JPEG, no less)! Of course, at first this is only a problem if you make it one (for yourself), but as a data interchange format, TIFF is a long way from being ideal. PNG is also a container-type format, but the structure of mandatory-vs-optional elements is much more rigorously defined.Sixth: PNG’s big strength is in the P : portable. the same file can be displayed on a phone, an iPad, any notebook or desktop machine regardless of whether it is a Mac, PC, or Linux (generally), because the rendering logic is built into all modern browsers (in fact, there are three little PNGs just below the text box in which I’m writing this).Seventh: the fact that any particular scanner does or does not support a given format is not intrinsically evidence of that format’s suitability for the task. Few scanner vendors care much about their software, and with higher-end applications like Silverfast, other considerations may apply (e.g. PNG requires compression, which requires CPU time, so saving files as uncompressed TIFFs is generally faster during the scan phase, although you may lose that time copying around larger files, and so on). Oddly enough, no-one’s mentioned JPEG2000, which is probably A Good Thing as it would just confuse the issue more (it’s another lossless format, but less well supported than PNG, so why bother .). Anyway, the bottom line is that whatever the source (camera, scanner, software) produces may well not be the best format for your personal workflow, and that format may not be the best for archival.Conclusion: (sorry it’s gone on this long ) there are plenty of subjective reasons to pick a file format, but when it comes to scanning there are no _objective_ reasons to pick TIFF over PNG or vice versa. Personally, I like to use PNG for scans, mainly because it’s also my final output (what gets sent to the printers), with all intermediate files (including the final master ) are in PSD. If someone batch scans stuff for me, it all gets converted to PNGs on arrival it only takes CPU time, and I’ve got plenty of that (as long as I’m not rendering video). This works for me, but probably wouldn’t for Curtis, but for my money the portability of PNG wins the day!(Why, yes, I have been bitten by unreadable file formats and incompatible TIFFs! How _did_ you guess?)