Here’s a script I use to create 2560xx1440 high quality backgrounds from images:
mkdir -p output
mogrify -fuzz 25% -trim -resize 2560x1440 -background white -gravity center -extent 2560x1440 -format jpg -quality 100 -path output *.jpg
It first creates the output directory than converts all jpgs in the directory to be 2560 by 1440 images trimmed of their borders then padded with white.