OCRmyPDF.sh: computation of resolution

Added compuation of resolution of each PDF page
Added extract of image of pgm if colorspace is Gray (to speed up
computation and save space)

OCRmyPDF.sh

@@ -1,62 +1,81 @@
 #!/bin/sh
 echo "usage: ./scan-archive.sh filename.pdf"
 
+LAN="eng"
+KEEP_TMP="1"
+
 infile="$1"
-lan="deu"
-dpi=300
 
 tmp="./tmp"
+FILE_SIZEPAGES="$tmp/infile-page-sizes.txt"
 
 # delete tmp files
 rm -r -f "${tmp}"
 mkdir -p "${tmp}"
 
-# detect the number of page of the pdf file
-numpages=`pdftk $infile "dump_data" | grep "NumberOfPages" | cut -f2 -d" "`
+# get the size of each pdf page (width / height) in pt (inch*72)
+echo "Extracting size of each page (in pt)"
+identify -format "%w %h\n" "$infile" > "$FILE_SIZEPAGES"
+sed -I "" '/^$/d' "$FILE_SIZEPAGES"	# removing empty lines (last one should be)
+numpages=`cat "$FILE_SIZEPAGES" | wc -l`
 echo "PDF file has $numpages pages"
 
 # Itterate the pages of the pdf file
 page="1"
-while [ $page -le $numpages ]; do
+cat "$FILE_SIZEPAGES" | while read pageSize ; do
 
-	# extract image from current pdf page
-	pdftk "$infile" cat $page output "${tmp}/${page}.pdf" > /dev/null
-
-	# get the size of the pdf (width / height) page in pt (inch*72)
-	# identify -format "return %w, %h\n" "${tmp}/${page}.pdf"
-	
-	# extract image from pdf file (keeping the resolution as available in the pdf file)
-	# pdfimages -f 1 -l 1 "${tmp}/${page}.pdf" ${page} 1>&2
-
-	# itterate the extracted images (there can be more than 1 image on the page)
-	# and get there respective number of x/y pixel 
-	# identify -format "return %w, %h\n" img1-xxx.ppm
-	
+	echo "Page $page: Computing embedded image resolution"
+	# get width / height of PDF page
+	heightPDF=`echo $pageSize | cut -f1 -d" "`
+	widthPDF=`echo $pageSize | cut -f2 -d" "`
+	# extract raw image from pdf file to compute resolution
+	# unfortunatelly this image may not be rotated as in the pdf...
+	# so we will have to extract it again later
+	pdfimages -f $page -l $page -j "$infile" "$tmp/${page}_orig" 1>&2	
+	# count number of extracted images
+	nbImg=`ls -1 "$tmp/${page}_orig"* | wc -l`
+	[ $nbImg -ne "1" ] && echo "Not exactly 1 image on page $page. Exiting" && exit 1
+	# Get the characteristic of the extracted image
+	origImg=`ls -1 "$tmp/${page}_orig"*`
+	origImg_woext=`echo "$origImg" | sed 's/\.[^.]*$//'`
+	origImg_ext=`echo "$origImg" | sed 's/^.*[.]//'`
+	propImg=`identify -format "%w %h %[colorspace]" "$origImg"`
+	heightImg=`echo "$propImg" | cut -f1 -d" "`
+	widthImg=`echo "$propImg" | cut -f2 -d" "`
+	colorspaceImg=`echo "$propImg" | cut -f3 -d" "`
 	# compute the resolution of the whole page (taking into account all images)
-	
-	
-	# extract the image with the right resolution
-	echo "Page $page: Extracting image from PDF"	
-	pdftoppm -r $dpi "${tmp}/${page}.pdf" > "${tmp}/${page}.ppm"
+	dpi=$(($heightImg*72/$heightPDF))
+	echo "Page $page: Resolution: ${dpi} dpi"
 
-	# improve quality of the image to get better ocr results
+	# extract current page as image with right rotation
+	echo "Page $page: Extracting image as ppm/pgm"
+	if [ $colorspaceImg == "Gray" ]; then
+		ext="pgm"
+		opt="-gray"
+	else
+		ext="ppm"
+		opt=""		
+	fi
+	pdftoppm -f $page -l $page -r $dpi $opt $infile > "${tmp}/${page}.$ext"
+
+	# improve quality of the image with unpaper to get better OCR results
 	echo "Page $page: Preprocessing image with unpaper"
 	unpaper --dpi $dpi --mask-scan-size 100 \
 		--no-grayfilter --no-blackfilter --no-mask-center --no-border-align \
-		--overwrite "$tmp/$page.ppm" "$tmp/$page.forocr.ppm" > /dev/null 
+		"$tmp/$page.$ext" "$tmp/$page.forocr.$ext" 1> /dev/null
 
 	# perform OCR
 	echo "Page $page: Performing OCR"
-	tesseract -l ${lan} "${tmp}/${page}.forocr.ppm" "${tmp}/${page}.hocr" hocr 1> /dev/null 2> /dev/null 
-	cp "${tmp}/${page}.hocr.html" "${tmp}/${page}.hocr"
+	tesseract -l "$LAN" "$tmp/$page.forocr.$ext" "$tmp/$page.hocr" hocr 1> /dev/null 2> /dev/null 
+	mv "${tmp}/${page}.hocr.html" "$tmp/$page.hocr"
 
 	# compress image to be put inside the pdf file
-	echo "Page $page: Compress image for final PDF file"
-	convert "${tmp}/${page}.forocr.ppm" "${tmp}/${page}.forpdf.jpg"
+	echo "Page $page: Compressing image for final PDF file"
+	convert -colorspace "$colorspaceImg" "$tmp/$page.forocr.$ext" "$tmp/$page.forpdf.jpg"
 	
 	# embed text and image to new pdf file
 	echo "Page $page: Embedding text in PDF"
-	python hocrTransform.py -r $dpi -i "${tmp}/${page}.forpdf.jpg" "${tmp}/${page}.hocr" "${tmp}/${page}-ocred.pdf"
+	python hocrTransform.py -r $dpi -i "$tmp/$page.forpdf.jpg" "$tmp/$page.hocr" "$tmp/${page}-ocred.pdf"
 	
 	# go to next page of the pdf
 	page=$(($page+1))