Okay so I'm hoping to help someone I know who does photography mainly as a hobby, but to a professional level (he did work professionally, but on a much more expensive work-provided system). However, the main problem he's having is that storing all the RAW image files is taking up a lot of space on his older iMac with its 500gb internal drive. Now I know it's possible to upgrade the drive in an iMac, but it's not really something we'd want to do if we can avoid it, plus he isn't generating loads of images, we just want to squeeze more out of the current capacity really. Anyway, I don't want to have to sacrifice the quality of the RAW files, but it occurs to me that there must be some other way to save them without the huge overhead it's having on the limited drive capacity (he's down to about 20gb free space!). My first thought was simply taking RAW files and compressing them into a zip archive, but while this ought to give decent savings this isn't great for convenience as they'd no longer appear in searches, and it's extra effort to open them if they are needed. I'm not super knowledgeable about other alternatives though; I understand that JPEG-2000 has some kind of lossless compression defined, but is this good enough to preserve a RAW file, or will other data be lost? Is it well-supported? Same question applies to PNG files, though I've also heard that these can actually end up larger than the original when dealing with such detailed files. There's also Adobe's DNG, which seems like it would be a good thing to convert to regardless, purely for non-device specific nature of them. But do these support lossless compression? He's got some 400gb of files, the biggest portion of which is RAW images, so even modest compression savings should make a big difference in the short term at least.