A script I quickly come up for my needs to extract image from pdf, preprocess and extract text with tesseract

pdfimages2txt

#!/bin/bash
STARTPAGE=2 
ENDPAGE=75 
SOURCE=book.pdf 
OUTPUT=book.txt 
RESOLUTION=600 
LAYOUT="1"

[[ -e out.txt ]] && rm out.txt
for i in `seq $STARTPAGE $ENDPAGE`; do
    echo processing page $i
    [[ ! -e page_"$i".png ]] && convert -colorspace Gray -crop 6704x5408+1894+0 -density $RESOLUTION $SOURCE\[$(($i - 1 ))\] page_"$i".png
    if [[ ! -e 8/page8_$i.png ]]; then
        convert -depth 8 -brightness-contrast +30x+100 page_"$i".png 8/page8_$i.png # need to convert to 8 color bit in order to make unpaper work
    fi 
    if [[ ! -e pages/page_"$i"_1.png || ! -e pages/page_"$i"_2.png  ]]; then
        echo "**** unpaper $i"
        rm page_"$i".pnm page_"$i"_1.pnm page_"$i"_2.pnm page_"$i"_1u.pnm page_"$i"_2u.pnm 2>/dev/null
        if [[ LAYOUT == "1" ]]; then 
            convert -crop 3352x5408+1894+0 8/page8_"$i".png 8/page8_"$i"_1.png 
            convert -crop 3352x5408+5246+0 8/page8_"$i".png 8/page8_"$i"_2.png 
            pngtopnm 8/page8_"$i"_1.png >page_"$i"_1.pnm        
            pngtopnm 8/page8_"$i"_2.png >page_"$i"_2.pnm        
            unpaper --layout single -dn left  -ds 1500 -dd 0.6 -dv 1.1 page_"$i"_1.pnm page_"$i"_1u.pnm
            unpaper --layout single -dn right -ds 1500 -dd 0.6 -dv 1.1 page_"$i"_2.pnm page_"$i"_2u.pnm
        else:
            pngtopnm 8/page8_$i.png >page_"$i".pnm        
            unpaper --layout double --output-pages 2 -dn left -ds 1500 -dd 0.6 -dv 1.1 -mw 350 page_"$i".pnm page_"$i"_%d.pnm
        fi
        convert page_"$i"_1u.pnm pages/page_"$i"_1.png
        convert page_"$i"_2u.pnm pages/page_"$i"_2.png
    fi
    
    tesseract pages/page_"$i"_1.png out -l deu
    echo "--------------------------------- pdf $i A ---------------------------------">> $OUTPUT
    cat out.txt >> $OUTPUT
    tesseract pages/page_"$i"_2.png out -l deu
    echo "--------------------------------- pdf $i B ---------------------------------">> $OUTPUT
    cat out.txt >> $OUTPUT
done

The different value for LAYOUT control the mode unpaper works with double layout performs the deskew comparing left and right side. I've tried both ways with mixed results, seems that --deskew-scan-size plays a big role in fixing incorrectly rotated images, test out what works best for your scanned pages.