XCF: bah, humbug! 9 59 2006-06-18T10:10:23-04:00 $Date: 2006-07-21 13:27:50 -0400 (Fri, 21 Jul 2006) $ NormanWalsh 2006Norman Walsh I know the calendar is almost exactly out of phase with Christmas, but “bah, humbug” anyway. Gimp's XCF file format is deliberately undocumented. Bah freaking humbug! [Update: a spec is under development!] I've been starting recently to take my photography a little more seriously. Partly, that means setting time aside sometimes just to try to improve my technique and to take a lot of (mostly mediocre, at best) pictures. (Taking lots is the only way I know to learn how to take better ones.) Partly, it means I've been trying to better understand and appreciate the digital image work flow process. And that means I've been spending more time in GIMP trying to understand how to process raw images from the camera and learn about things like layer masks and sharpening. And now I learn that GIMP's native file format, XCF, is not merely undocumented, it is intentionally undocumented.
Danger, Will Robinson! Undocumented binary black hole! Danger!
I don't claim any particular expertise in designing graphic file formats, though I've reverse engineered a few simple ones in my day, but the right answer here seems pretty clear. As near as I can tell, an XCF file consists, logically, of several bitmaps of varying sizes and depths, some metadata relating them, and a bunch of ancillary data (palettes, brushes, selections, etc.). Pick some straightforward encoding for the bitmaps (RLE, LZW, or anything lossless, really), design an XML format for the rest of the data, and package them all together somehow (maybe ZIP, maybe something else). I don't see any particular merit in base64 or otherwise encoding the binary data directly into the XML, but I don't see why that should prevent the rest of the data from being in XML. I really don't know, right now, what the right answer is, but pouring more of my heart and soul into someone's proprietary black hole isn't it. Bah #@$&!?% humbug! [Update, 20 June 2006: Based on Sven's comments below and other postings, it seems that perhaps the situation isn't as dire as it first appears. I hope this turns out to be the case, because I really care about this data.] [Update, 21 July 2006: Dave Neary reports that Henning Makhomlm has stepped up to write a specification for the XCF format. Good on ya, Henning!