https://github.com/POV-Ray/povray/releases/tag/v3.8.0-alpha.9861167


Primary feature of this update is the addition of blue noise dithering.

Blue noise dithering is a comparatively new ordered dithering algorithm,
using a tiling pattern to vary the quantization threshold. However,
unlike the extremely regular pattern used in the otherwise similar Bayer
dithering, the pattern used in blue noise dithering is constructed to be
extremely irregular at small scales, while at the same time being
extremely regular at large scales. In other words, it has a lot of
high-frequency noise, while at the same time having very little
low-frequency noise.

The pattern used by POV-Ray is a hard-coded 64x64 pattern, generated
using a so-called void-and-cluster approach (utilizing a public domain
Python script by - as it happens - fellow "Rheinlandian", 3D enthusiast
and namesake Christoph Peters).

Due to its high quality and ease of use, blue noise dithering is now the
default algorithm, and is also used in the preview window, replacing the
inferior Bayer dithering there.


The blue noise dithering comes in two variants: Aside from a
straightforward implementation (`+THbn`) where the threshold of all
channels is varied according to the same pattern, an experimental
implementation is available (`+THbnx`) in which the threshold for the
red and blue channels is varied according to the inverse of the pattern,
to reduce the noise in the brightness domain (at the cost of more noise
in the chromaticity domain).


In the wake of this, ...

- A couple more error diffusion dithering filters have been added
(primarily for giggles and because we can). See
povray.documentation.inbuilt, recent thread "Some stuff related to
output file formats" for details.

- The lower limit for the bit depth (previously 5) has been dropped;
anything between 1 and 16 is fair game now (affects PNG and PPM/PGM
only; again, mostly for giggles, to better demonstrate dithering, but
maybe some of you folks may want to experiment with it).

- Greyscale output no longer forces bit depth to 16 (also primarily for
dithering demonstration purposes).

- Greyscale file output now also switches the preview window to greyscale.

- The `+F` option can now be used to specify both greyscale (`g` suffix)
and non-default bit depth (numeric suffix) simultaneously. (The `g` must
come first.)

- Gamma handling in PGM (greyscale "PPM") files has been changed to be
consistent with colour PPM.

- Gamma handling in dithering has been improved.


I /think/ that's all.

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