These options control some of the internals of darktable.
In order to speed-up display of film rolls, darktable stores thumbnails in a cache file on disk (primary cache) and loads it into memory at startup. This value controls the cache size in megabytes. It needs a restart if changed (default 256MB).
If activated darktable stores all thumbnails on disk as a secondary cache, and thereby keeping thumbnails accessible in case they get dropped from the primary cache. This needs more disk space but speeds up lighttable view as it avoids reprocessing of thumbnails (default on).
If activated darktable generates thumbnails in a general color space (AdobeRGB) in order to render them independently of the individual monitor. Conversion to the monitor color space is done at display time. If this option is not activated thumbnails are directly stored in the specific monitor color space valid at generation time and are subsequently displayed without further corrections (default on).
This controls how many parallel threads are used to create thumbnails during import. On 32bit systems it is strongly recommended to set this to 1. Needs a restart if changed (default 2).
In order to manage large images on systems with limited memory darktable does tile-wise processing. This variable controls the maximum amount of memory (in MB) a module may use during image processing. Lower values will force memory hungry modules to process an image with increasing number of tiles. Setting this to 0 will omit any limits. Values below 500 will be treated as 500. On a 32bit system you should set this to 500. Needs a restart if changed (default 1500).
If set to a positive, non-zero value, this variable defines the minimum amount of memory (in MB) that darktable should take for a single tile. On a 32bit system you should set this to 8. 64bit systems can live with higher values. Needs a restart if changed (default 16).
These redundant XMP files can later be re-imported into a different database, preserving your changes to the image. It's strongly recommended to have this option activated so you don't lose data in case of a database corruption. Backing up your raw file plus the accompanying XMP file will allow you to fully restore your work (default on).
Entries in XMP tags can get rather large and may exceed the available space to store the history stack in output files on export. This option allows binary XMP tags to be compressed in order to save space. Available options are “never”, “always”, and “only large entries” (default).
darktable can use your GPU to speed up processing significantly. Interface OpenCL requires suitable hardware and matching OpenCL drivers on your system. If one of those is not found the option is greyed out. Can be switched on and off at any time and takes immediate effect (default on).
If this option is activated, darktable will use system library LittleCMS 2 instead of its own routines. This is significantly slower than the default but might give more accurate results in some cases (default off).
Note that if the given ICC is LUT-based or contains both, a LUT and a matrix, darktable will use LittleCMS 2 to render the colors regardless of this configuration parameter's value.
The image will first be processed in full resolution, and downscaled at the very end. This can result in better quality sometimes, but will always be slower (default off).
Interpolation when not viewing 1:1 in darkroom mode: “always bilinear (fast)” is fastest, but not as sharp. “at most ppg (reasonable)” is using ppg + interpolation modes specified below, “full (possibly slow)” will use exactly the settings for full-size export (default “at most ppg (reasonable)”).
Pixel interpolator used in rotation, lens correction, up-and-down scaling; options are “bilinear”, “bicubic”, “lanczos2”, “lanczos3” (default).
The storage backend for password storage. Options: “auto” (default), “none”, “libsecret”, “kwallet”.
Check file modification times of all XMP files on startup to find out if any got updated in the meantime by some other software. If updated XMP files are found a menu opens for the user to decide which of the XMP files to be reloaded – replacing darktable's database entries by the XMP file contents – and which of the XMP files to be overwritten by darktable's database. Activating this option also causes darktable to check for text sidecar files that have been added after import time – see option “overlay txt sidecar over zoomed images” in Section 8.1, “GUI options” (default off).
Defines an external program which is used in the lighttable view to play audio files that some cameras record to keep notes for images (default “aplay”).
Use the per-camera basecurve by default instead of the generic manufacturer one if there is one available. For more details see Section 188.8.131.52, “Base curve” (default off).