On Sat, Dec 5, 2015 at 1:03 AM, Anton Aylward <li...@antonaylward.com> wrote: > On 12/04/2015 05:14 PM, Pedro Côrte-Real wrote: >>> > Joe-Random edits can be destructive, but specific edits can be purposeful. >> This isn't a matter of "wouldn't it be good if we could edit raw >> files", it possibly would be. It's a matter of these formats being so >> poorly defined it's simply not safe to do it. If you want your files >> to survive and be readable in the future just don't do it. > > So? > As I say, its not as if I'm doing random edits or working with undefined > fields. I'm not editing the RAW data, just the extant exif fields.
There's no such thing. TIFF files (which most raws are) are absolute addressed. So if you change a well known field like "Copyright" the length of the EXIF block changes. So what exiftool does is go through the whole file and change offsets of all sorts of fields to make this work. This is a very dangerous thing to do and there's no way to guarantee it will work properly for these formats. You may think you're editing "just the extant exif fields" but you're actually doing a very deep rewrite of the whole file. >While I agree with you in the global sense that exif is poorly defined, >the changes I'm talking about are with well defined - as in previously >defined but absent fields. Its not as if I'm screwing around with the >DPI or lens settings! Yes there are a lot of ill-defined and/or >critical exif values. I'm not talking about those, leave them along. >leave the DATA alone as well. Ignore my warning at your peril but this is simply not true. EXIF is actually very well defined it's the raw format encapsulating it that isn't and changing things in the EXIF has a very good chance of breaking things in other places in the file. I know these formats better than most (I've written the rawspeed support for quite a few of them) and I don't trust any tool to get these rewrites correct. You shouldn't either. >But under *some* circumstances someone who knows his camera well enough, >can address *very* *specific* use cases to alter *some* and *only *some* >exif fields. Knowing your camera buys you nothing only the illusion that you know what you are doing. It's exiftool (or whatever you are using) that would have to understand the *format* completely. Since exiftool tries really hard to do the whole file rewrite that's needed properly you may not notice anything breaking immediately but there's a good chance it did and there's no point in taking that chance. Never edit raws, never convert to DNG, just edit XMPs when you need to make changes to the metadata. Exiftool can be used to make the XMP changes too. Cheers, Pedro ------------------------------------------------------------------------------ Go from Idea to Many App Stores Faster with Intel(R) XDK Give your users amazing mobile app experiences with Intel(R) XDK. Use one codebase in this all-in-one HTML5 development environment. Design, debug & build mobile apps & 2D/3D high-impact games for multiple OSs. http://pubads.g.doubleclick.net/gampad/clk?id=254741911&iu=/4140 _______________________________________________ Darktable-users mailing list Darktable-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/darktable-users
