manga upscaling

Upscaling stuff with 4x digimanga v2 and other stuff

Downscaling use imagemagick, although I feel like using VapourSynth would be better since I can do a lot more post-processing.

Halftones:
 - magick mogrify -format png -alpha off -colorspace Gray -level 0.2%,100% -filter Catrom -resize xXXXX -monitor -path ./output/ ./input/*.png
Gray/Color:
 - magick mogrify -format png -alpha off -filter RobidouxSharp -resize xXXXX -monitor -path ./output/ ./input/*.png
 
Alpha off and colorspace Gray to force grayscale, level to 0.2% black since black level are not really #000000 sometimes.

Reasoning for kernel filter:
- Catrom, works nice on half-tones to give that sharper look, this has minimal halo-ing and a bit more jagged lines
- RobidouxSharp, a sharper version for Robidoux. You can also try Robidoux to see if you prefer it more.
   This give a nice sharp image with less halo and smoother lines. Works better on gray/color image.