#!/bin/sh

for f in *.[jJ][pP][gG]; do
    convert "$f" -respect-parenthesis \( -clone 0 -set colorspace RGB -colorspace gray -negate -lat 15x15+5% -contrast-stretch 0 \) \
        -compose copy_opacity -composite -fill "white" -opaque none -alpha off "_$f"

done

convert -quality 85 _*.[jJ][pP][gG] -adjoin merged.pdf