Automatic oversampling
- If resolution is too low (<250dpi) perform automatic oversampling of the image - comments improved - log messages improved
This commit is contained in:
fritz-hh
+48
-26
@@ -8,7 +8,7 @@
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. "./src/config.sh"
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# Initialization of variables passed by args
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# Initialization of variables passed by arguments
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FILE_INPUT_PDF="$1" # PDF file containing the page to be OCRed
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PAGE_INFO="$2" # Various characteristics of the page to be OCRed
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NUM_PAGES="$3" # Total number of page of the PDF file (required for logging)
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@@ -19,34 +19,47 @@ KEEP_TMP="$7" # Keep the temporary files after processing (helpful for debugg
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PREPROCESS_DESKEW="$8" # Deskew the page to be OCRed
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PREPROCESS_CLEAN="$9" # Clean the page to be OCRed
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PREPROCESS_CLEANTOPDF="${10}" # Put the cleaned paged in the OCRed PDF
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PDF_NOIMG="${11}" # Request to generate also a pdf page containing only the OCRed text but no image (helpful for debugging)
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PDF_NOIMG="${11}" # Request to generate also a PDF page containing only the OCRed text but no image (helpful for debugging)
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TESS_CFG_FILES="${12}" # Specific configuration files to be used by Tesseract during OCRing
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##################################
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# Detect the characteristics of the embedded image
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# Detect the characteristics of the embedded image for
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# the page number provided as parameter
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#
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# Params:
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# return :
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# Param 1: page number
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# Param 2: PDF page width in pt
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# Param 3: PDF page height in pt
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# Param 4: temp file path (Path of the file in which the output should be written)
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# Output: A file (<pagenum>-img-characteristics.txt) containing the characteristics of the embedded image
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# Structure of the file:
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# <dpi> <colorspace>
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# Returns:
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# - 0: if no error occurs
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# - 1: in case the page contains more than one image
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# - 2: in case the x,y resolutions are not equal
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##################################
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imageCharacteristics() {
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local page widthPDF heightPDF nbImg curImg propCurImg widthCurImg heightCurImg colorspaceCurImg tmpval dpi_x dpi_y epsilon dpi
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local page widthPDF heightPDF curImgCharacteristics nbImg curImg propCurImg widthCurImg heightCurImg colorspaceCurImg tmpval dpi_x dpi_y epsilon dpi
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# width / height of PDF page (in pt)
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# page number
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page="$1"
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# width / height of PDF page (in pt)
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widthPDF="$2"
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heightPDF="$3"
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# path of the file in which the output should be written
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curImgCharacteristics="$4"
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[ $VERBOSITY -ge $LOG_DEBUG ] && echo "Page $page: size ${heightPDF}x${widthPDF} (h*w in pt)"
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[ $VERBOSITY -ge $LOG_DEBUG ] && echo "Page $page: Size ${heightPDF}x${widthPDF} (h*w in pt)"
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# extract raw image from pdf file to compute resolution
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# unfortunately this image can have another orientation than in the pdf...
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# so we will have to extract it again later using pdftoppm
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pdfimages -f $page -l $page -j "$FILE_INPUT_PDF" "$curOrigImg" 1>&2
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# count number of extracted images
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nbImg=`ls -1 "$curOrigImg"* | wc -l`
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[ $nbImg -ne "1" ] && echo "Page $page: Expecting exactly 1 image on page $page (found $nbImg). Exiting..." >&2 && exit $EXIT_BAD_INPUT_FILE
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[ $nbImg -ne "1" ] && echo "Page $page: Expecting exactly 1 image on page $page (found $nbImg). Exiting..." >&2 && return 1
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# Get characteristics of the extracted image
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curImg=`ls -1 "$curOrigImg"*`
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propCurImg=`identify -format "%w %h %[colorspace]" "$curImg"`
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@@ -62,30 +75,33 @@ imageCharacteristics() {
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heightCurImg=$widthCurImg
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widthCurImg=$tmpval
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fi
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[ $VERBOSITY -ge $LOG_DEBUG ] && echo "Page $page: size ${heightCurImg}x${widthCurImg} (h*w pixel)"
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[ $VERBOSITY -ge $LOG_DEBUG ] && echo "Page $page: Size ${heightCurImg}x${widthCurImg} (h*w pixel)"
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# compute the resolution of the image
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dpi_x=`echo "scale=5;$widthCurImg*72/$widthPDF" | bc`
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dpi_y=`echo "scale=5;$heightCurImg*72/$heightPDF" | bc`
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# round the dpi values to the nearest integer
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rounded_dpi_x=`echo "scale=5;$dpi_x+0.5" | bc` # adding 0.5 is required for rounding
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rounded_dpi_x=`echo "scale=0;$rounded_dpi_x/1" | bc` # round to the nearest integer
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rounded_dpi_y=`echo "scale=5;$dpi_y+0.5" | bc` # adding 0.5 is required for rounding
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rounded_dpi_y=`echo "scale=0;$rounded_dpi_y/1" | bc` # round to the nearest integer
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# take the biggest dpi value
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[ $rounded_dpi_x -ge $rounded_dpi_y ] && dpi=$rounded_dpi_x || dpi=$rounded_dpi_y
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[ $VERBOSITY -ge $LOG_INFO ] && echo "Page $page: Embedded image resolution is $dpi dpi"
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# save the image characteristics
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echo "$dpi $colorspaceCurImg" > $curImgCharacteristics
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# check the x,y resolution difference that can be cause by:
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# - the truncated PDF width/height in pt
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# - the precision of dpi values computed above
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epsilon=`echo "scale=5;($widthCurImg*72/$widthPDF^2)+($heightCurImg*72/$heightPDF^2)+0.00002" | bc` # max inaccuracy due to truncation of PDF size in pt
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[ $VERBOSITY -ge $LOG_WARN ] && [ `echo "($dpi_x - $dpi_y) < $epsilon " | bc` -eq 0 -o `echo "($dpi_y - $dpi_x) < $epsilon " | bc` -eq 0 ] \
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&& echo "Page $page: (x/y) resolution mismatch ($dpi_x/$dpi_y). Difference should be less than $epsilon. Taking biggest value"
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&& echo "Page $page: (x/y) resolution mismatch ($dpi_x/$dpi_y). Difference should be less than $epsilon. Taking biggest value" && return 2
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# round the dpi values to the nearest integer
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dpi_x=`echo "scale=5;$dpi_x+0.5" | bc` # adding 0.5 is required for rounding
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dpi_x=`echo "scale=0;$dpi_x/1" | bc` # round to the nearest integer
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dpi_y=`echo "scale=5;$dpi_y+0.5" | bc` # adding 0.5 is required for rounding
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dpi_y=`echo "scale=0;$dpi_y/1" | bc` # round to the nearest integer
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# take the biggest x,y dpi value
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[ $dpi_x -ge $dpi_y ] && dpi=$dpi_x || dpi=$dpi_y
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# save the image characteristics
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echo "$dpi $colorspaceCurImg" > $curImgCharacteristics
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# everything went well!
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return 0
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}
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@@ -107,14 +123,20 @@ curImgCharacteristics="$TMP_FLD/${page}-img-characteristics.txt" # Detected char
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# auto-detect the characteristics of the embedded image
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if ! imageCharacteristics "$page" "$widthPDF" "$heightPDF"; then
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echo "problem detected. Exiting...."
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fi
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imageCharacteristics "$page" "$widthPDF" "$heightPDF" "$curImgCharacteristics"
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case "$?" in
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1) exit $EXIT_BAD_INPUT_FILE ;;
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esac
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# read the image characteristics
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dpi=`cat "$curImgCharacteristics" | cut -f1 -d" "`
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colorspaceCurImg=`cat "$curImgCharacteristics" | cut -f2 -d" "`
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# perform oversampling if the resolution is not big enough
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# to get good OCR results
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[ $dpi -lt 250 ] && dpi=250 && [ $VERBOSITY -ge $LOG_WARN ] \
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&& echo "Page $page: Low image resolution detected. Performing oversampling (at $dpi dpi) to try to get better OCR results. This will probably increase output file size."
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# Identify if page image should be saved as ppm (color) or pgm (gray)
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ext="ppm"
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opt=""
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