Documentation of Bilateral-blur default intensity sigma

ImageMagick version

7.1.2-2

Operating system

Windows

Operating system, version and so on

Windows 11

Description

https://imagemagick.org/command-line-options/#update&gsc.tab=0 says:

The default value for the intensity and spatial sigmas are 0.75*diameter and 0.25*diameter respectively.

However, the code in MagickWand/mogrify.c and MagickWand/operation.c has the default for intensity at 1.0*diameter.

We can demonstrate that the factor used is 1.0. Note that width=10 and height=10 makes diameter=14.14, and 75% of that is 10.6.

D:\temp>%IMG7%magick toes.png -bilateral-blur 10x10 x0.png

D:\temp>%IMG7%magick toes.png -bilateral-blur 10x10+14.14 x14.png

D:\temp>%IMG7%magick toes.png -bilateral-blur 10x10+10.6 x10.png

D:\temp>%IMG7%magick compare -metric RMSE x0.png x14.png NULL:
0.286713 (4.37495e-06)
D:\temp>%IMG7%magick compare -metric RMSE x0.png x10.png NULL:
235.779 (0.00359775)

So the default is very close to the explicit intensity 14.14, which is diameter*1.0.

Looking at "blame" for the source code, the factor has always been 1.0. Thus I suggest the documentation is changed to match the code:

The default value for the intensity and spatial sigmas are 1.0*diameter and 0.25*diameter respectively.

Steps to Reproduce

See above.

Images

Start with the bilateral-blur documentation at the linked command-line-options page and compare its stated defaults with the behavior described using the magick and compare commands. The source locations mentioned are MagickWand/mogrify.c and MagickWand/operation.c; done means the documentation states 1.0diameter for intensity and 0.25diameter for spatial sigma.