I am pretty sure that sigmoidization is now a dead prototype: http://www.imagemagick.org/discourse-server/viewtopic.php?f=1&t=25736&p=113272#p113272
Thanks for the progress update.
I'm also wondering if another approach could be easily implemented in ImageMagick. What most of the efforts sofar attempt to do is upsample and minimize artifacts (halo, ringing, blocking, some aliasing). The results look pretty useful. Most filters also attempt to improve the contrast compared to a simple bilinear interpolation (Triangle filter).
However, what about a version of upsampling that is not trying to increase sharpness when upsampling (maybe 'Gaussian'), and add
some deconvolution to compensate for the upsampling losses. I understand that it is difficult to dynamically adjust the required (probably Gaussian) PSF radius with variable upsampling percentages, but that would not be too much of an issue if one uses fixed percentages in a batch/script file instead of from the command line console.
Here is an example for a 300% upsample (Windows batch file formatting, allows drag and drop):
convert %1 -filter Gaussian -distort Resize 300%% -define convolve:scale=^100%%,100 -morphology Convolve DoG:0,0,1.7 "%~dpn1_Gauss+HighPass.png"
The 100% part in the "-define convolve:scale=^100%
%,100" parameter, allows to modify the 'amount' of High-pass sharpening. The 1.7 part of the "-morphology Convolve DoG:0,0,1.7
" parameter allows to adjust the 'sigma' of the Gaussian High-pass.
This would have the benefit of allowing to control the upsampling artifacts through choice of resampling filter (e.g. Gaussian), and restore some sharpness by using a targeted approach (e.g. High-pass) which should not produce halos (or at least relatively controllable ones) if well dimensioned, or can be used to add a bit of halo to pre-compensate for later losses in our output medium (e.g. ink diffusion).
Of course a real iterative deconvolution method would be able to do an even better job than a simple single High-pass convolution sharpening.
Just some food for thought ...