Image Magick

convert image stdin -> stdout into greyscales

convert -colorspace Gray - -

white background to transparent/alpha with imagemagick/mogrify

mogrify -fuzz 10% -transparent white myimage.png

fuzz helps converting white-ish colors, increase if not enough

imagemagick convert from a.png to b.png with size 128x128 centered and background white

magick ? -resize 128x128 -background white -gravity center -extent 128x128 icon.png

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