- comments to splitting part in watermark.sh

watermark.sh

@@ -20,8 +20,8 @@ Options:
   -o, --out       output folder. Default: ./pdfs_watermarked
   -c, --cores     number of cores for parallel processing. Default: 1
   -d, --dpi       dpi parameter for conversion from pdf to images. Default: 250
-  -s, --split     flag to split A3 pages to A4 and resorts them
-  -q, --quality   quality parameter for jpeg. Default: 25"
+  -q, --quality   quality parameter for jpeg. Default: 25
+      --splita3   flag to split A3 landscape pages to A4 portrait pages and resorts them"
 
 # -allow a command to fail with !’s side effect on errexit
 # -use return value from ${PIPESTATUS[0]}, because ! hosed $?
@@ -31,8 +31,8 @@ if [[ ${PIPESTATUS[0]} -ne 4 ]]; then
     exit 1
 fi
 
-OPTIONS=hiocdsqv
-LONGOPTS=help,in:,out:,cores:,dpi:,split,quality:,verbose
+OPTIONS=hiocdqv
+LONGOPTS=help,in:,out:,cores:,dpi:,splita3,quality:,verbose
 
 # -regarding ! and PIPESTATUS see above
 # -temporarily store output to be able to check for errors
@@ -75,7 +75,7 @@ while true; do
       quality="$2"
       shift 2
       ;;
-    -s|--split)
+    --splita3)
       split=y
       shift 1
       ;;
@@ -184,31 +184,48 @@ doit () {
     exit
   fi
 
-  # convert pdf into images
+  # Convert PDF into images
+  # This may take a while depending on ${dpi} 
+  # (which should not be set to a higher value than the DPI of the scanning device!)
   echo
   echo "Convert PDF into images"
   pdftoppm -r ${dpi} -png $longinpdf "${tmpfolder}"/page
 
-  # Split
+  # Split A3 pages
+  # scanning exams with the feeder of the copy machine results in double paged A3
+  # here, we split these A3 pages into two A4 ones and resort them accordingly
+  # which is the inverse of "brochure print"
   if [[ "$split" = "y" ]]; then
     echo
-    echo "Split PDF A3 pages into A4"
+    echo "Split landscape A3 pages into each two portrait A4 pages"
     
-    # rename a3 pages
+    # rename A3 pages
     for longpage in "${tmpfolder}"/page*.png; do
       page=$(basename "${longpage}")
       mv "$longpage" "${tmpfolder}/tmppage_a3${page}"
     done
 
-    
     pcnt=1
     for longa3page in "${tmpfolder}"/tmppage_a3*.png; do
       echo "${longa3page}"
 
-      # Split landscape A3 into two portrait A4
+      # Split landscape A3 page into two portrait A4 pages
       convert "${longa3page}" -crop 50%x100% +repage "${tmpfolder}"/tmppage_a4_%02d.png
 
       # Reorder
+      # Example: 4 A3 pages, printed on both sides
+      # yields a brochure with 16 A4 pages
+      #
+      # 1st A3 page     2nd A3 page     3rd A3 page   ...  8th A3 page
+      # |-----,-----|   |-----,-----|   |-----,-----|     |-----,-----|
+      # |--16-,---1-|   |---2-,--15-|   |--14-,---3-|     |---8-,---9-|
+      # |-----,-----|   |-----,-----|   |-----,-----|     |-----,-----|
+      # 
+      # results in
+      # 1st A4     2nd A4  ... 16th A4 page
+      # |-----|    |-----|     |-----| 
+      # |---1-|    |---2-|     |--16-|  
+      # |-----|    |-----|     |-----|    
       numdoublepage=$(find "${tmpfolder}"/ -type f -name "tmppage_a3*.png" | wc -l)
       numsinglepage=$(( numdoublepage*2 ))
       
@@ -220,7 +237,7 @@ doit () {
         numdest2=$(( pcnt ))
       fi
 
-      # Convert to %02d format # TODO: this must be simpler!
+      # Convert to %02d format # TODO: this should be obtained simpler!
       if [[ ${#numdest1} -lt 2 ]] ; then
         numdest1="00${numdest1}"
         numdest1="${numdest1: -2}"
@@ -242,6 +259,7 @@ doit () {
     rm "$tmpfolder"/tmppage_*.png
   fi ## split
 
+
   # Watermarking
   echo
   echo "Watermarking"