This module eliminates some of the banding artifacts that can result when darktable’s internal 32-bit floating point data is transferred into discrete 8-bit or 16-bit integer output format for display or export.
Although not an inherent problem in any of darktable’s modules, some operations may provoke banding if they produce a lightness gradient in the image. To mitigate possible artifacts you should consider activating dithering when using the vignetting or graduated density modules. This is especially relevant for images with extended homogeneous areas such as cloudless sky. Also watch out for banding artifacts when using a gradient drawn mask.
Viewing an image dithered into a very low bit depth from some distance (e.g. “floyd-steinberg 1-bit b&w”) will give the impression of a homogeneous grayscale image. darktable attempts to mimic this impression when rendering zoomed-out images in the center view, the navigation window and thumbnails. This is accomplished by dithering those images into a higher number of grayscale levels. Note that, as a consequence, the histogram – which is derived from the navigation window – will show this increased number of levels and is therefore not a full match to the output image.
- Choose the dithering method to use.
floyd-steinberg: Systematically distribute quantization errors over neighboring pixels. This method can be selected with some typical output bit depths. Alternatively, you can select floyd-steinberg auto, which automatically adapts to the desired output format.
random dithering: This method just adds some level of randomness to break sharp tonal value bands.
- damping (“random” method only)
- Controls the level of added random noise expressed as a damping factor in a 10*log 2 basis. A value of -80 is a good fit for 8-bit output formats; -160 for 16-bit output.