Exporting from raw to jpeg with darktable: a few things I’ve observed

I’ve been playing around with exporting to jpeg lately, because after our recent Easter holiday I had a few hundred pics to process – some of which might get shared with family. In parallel with this I’ve been building Darktable from git master and was racking my brains trying to work out why the export process (from what is effectively a nightly build) was giving me useless output files. By “useless” I mean “had no content except for EXIF info”. Very, very annoying.

After firing up badopen.d and while testing the various intent and profile settings for exporting to file-based storage, I realised that stacks such as this:

0 100408                    openat:return open for '/opt/darktable/share/darktable/color/out/image' failed
             libc.so.1`syscall+0x5
             libc.so.1`__open+0x29
             libc.so.1`open+0xd4
             libc.so.1`_endopen+0xa1
             libc.so.1`fopen+0x29
             liblcms2.so.2.0.3`cmsOpenIOhandlerFromFile+0x73
             liblcms2.so.2.0.3`cmsOpenProfileFromFileTHR+0x4c
             liblcms2.so.2.0.3`cmsOpenProfileFromFile+0x2c
             libdarktable.so`dt_colorspaces_create_output_profile+0x3e4
             libjpeg.so`write_image+0x173
             libdarktable.so`dt_imageio_export_with_flags+0x55e
             libdarktable.so`dt_imageio_export+0xfb
             libdisk.so`store+0x38f
             libdarktable.so`dt_control_export_job_run._omp_fn.0+0x40b
             libdarktable.so`dt_control_export_job_run+0x345
             libdarktable.so`dt_control_run_job+0x21c
             libdarktable.so`dt_control_work+0x41
             libc.so.1`_thrp_setup+0x9d
             libc.so.1`_lwp_start

were probably indicative of something strange in LCMS-land. Sure enough, the ‘always use littlecms2 when exporting’ box was ticked in the core options dialog. Turning that off made a world of difference – no more empty images! I assume that if I can locate an LCMS2 output profile then I’d have more success using it

For giggles (and because I’m still annoyed by this ticket, I decided to go through all the export options and compare the output: