From 96497d7327547e6464e53902cf58aec378c974c4 Mon Sep 17 00:00:00 2001 From: Eric Ihli Date: Tue, 14 Apr 2020 08:05:42 -0700 Subject: [PATCH] Add doc for shell script to parse text from table Add notes for improving accuracy. --- pdf_table_extraction_and_ocr.org | 59 +++++++++++++++++++++++---- table_ocr/extract_cells_from_table.py | 2 +- 2 files changed, 51 insertions(+), 10 deletions(-) diff --git a/pdf_table_extraction_and_ocr.org b/pdf_table_extraction_and_ocr.org index 00a02a0..b77687b 100644 --- a/pdf_table_extraction_and_ocr.org +++ b/pdf_table_extraction_and_ocr.org @@ -20,7 +20,19 @@ some unnecessary output is printed in the ~*Python*~ buffer. Adding ~:results output~ to a code block will minimize that noise. #+END_COMMENT -* Preparing our data +* Overview + +** To get CSV data from a table in a scanned pdf document: + +* +#+BEGIN_SRC shell +python -m table_ocr.prepare_pdfs /tmp/example-1/example-1.pdf /tmp/example-2/example-2.pdf > /tmp/pdf-images.txt +cat /tmp/pdf-images.txt | grep .png | xargs -I{} python -m table_ocr.extract_tables {} +find /tmp -iregex ".*example.*table.*\.png" 2>/dev/null | xargs -I{} python -m table_ocr.extract_cells_from_table {} +find /tmp -iregex ".*example.*cells.*\.png" 2>/dev/null | xargs -I{} python -m table_ocr.ocr_image {} + +#+END_SRC +* Preparing data ** Converting PDFs to images Not all pdfs need to be sent through OCR to extract the text content. If you can @@ -168,6 +180,20 @@ cv2.imwrite("resources/examples/example-table.png", image) #+ATTR_HTML: :width 500px :height 100% [[file:resources/examples/example-table.png]] +** Improving accuracy + +It's likely that some images will contain tables that aren't accurately +recognized by the code above. The code will then need to be made more robust. +But how will we know that changes to the code don't break the detection of +tables that were previously detected? + +It might be good to add some type of test suite in the future that contains a +spec that matches a pdf with the pages and pixel coordinates of the detected +tables. The coordinates would need to have a range. Something like +"example-1.pdf, page-2.png, [450:470, 200:210, 800:820, 1270:1290]" where the +elements of the list are valid x, y, w, h ranges. So the test will pass if if +the x, y, width and height are anywhere in that range. + * OCR tables Find the bounding box of each cell in the table. Run tesseract on each cell. @@ -175,7 +201,7 @@ Print a comma seperated output. We'll start with an image shown at the end of the previous section. -*** Blur +** Blur Blurring helps to make noise less noisy so that the overall structure of an image is more detectable. @@ -205,7 +231,7 @@ cv2.imwrite("resources/examples/example-table-blurred.png", blurred) #+ATTR_HTML: :width 500px :height 100% [[file:resources/examples/example-table-blurred.png]] -*** Threshold +** Threshold We've got a bunch of pixels that are gray. Thresholding will turn them all either black or white. Having all black or white pixels lets us do morphological @@ -237,7 +263,7 @@ cv2.imwrite("resources/examples/example-table-thresholded.png", img_bin) #+ATTR_HTML: :width 500px :height 100% [[file:resources/examples/example-table-thresholded.png]] -*** Finding the vertical and horizontal lines of the table +** Finding the vertical and horizontal lines of the table Note: There's a wierd issue with the results of the example below when it's evaluated as part of an export or a full-buffer evaluation. If you evaluate the @@ -270,7 +296,7 @@ cv2.imwrite("resources/examples/example-table-lines.png", mask) #+ATTR_HTML: :width 500px :height 100% [[file:resources/examples/example-table-lines.png]] -*** Finding the contours +** Finding the contours Blurring and thresholding allow us to find the lines. Opening the lines allows us to find the contours. @@ -334,7 +360,7 @@ bounding_rects = [b for b in bounding_rects if b is not largest_rect] cells = [c for c in bounding_rects] #+END_SRC -*** Sorting the bounding rectangles +** Sorting the bounding rectangles We want to process these from left-to-right, top-to-bottom. @@ -445,7 +471,7 @@ cv2.imwrite("resources/examples/example-table-cell-1-1.png", cell_images_rows[1] #+ATTR_HTML: :width 200px :height 100% [[file:resources/examples/example-table-cell-1-1.png]] -*** Cropping each cell to the text +** Cropping each cell to the text OCR with Tesseract works best when there is about 10 pixels of white border around the text. @@ -487,7 +513,22 @@ cv2.imwrite("resources/examples/example-table-cell-1-1-cropped.png", image) #+ATTR_HTML: :width 200px :height 100% [[file:resources/examples/example-table-cell-1-1-cropped.png]] -*** OCR each cell +#+HEADER: :post html-image-size(text=*this*, width="200px") +#+BEGIN_SRC python :noweb no-export :results raw :exports both +import cv2 +<> +image = cv2.imread("/tmp/example-1/cells/001-002.png", cv2.IMREAD_GRAYSCALE) +image = crop_to_text(image) +cv2.imwrite("/tmp/example-1/cells/001-002-cropped.png", image) +"/tmp/example-1/cells/001-002-cropped.png" +#+END_SRC + +#+RESULTS: +#+ATTR_HTML: :width 200px :height 100% +[[file:/tmp/example-1/cells/001-002-cropped.png]] + + +** OCR each cell If we cleaned up the images well enough, we might get some accurate OCR! @@ -723,7 +764,7 @@ def main(f): cell_filename = "{:03d}-{:03d}.png".format(i, j) path = os.path.join(cell_img_dir, cell_filename) cv2.imwrite(path, cell) - print(cell_filename) + print(path) <> diff --git a/table_ocr/extract_cells_from_table.py b/table_ocr/extract_cells_from_table.py index 2dcbbd4..6d2cc4a 100644 --- a/table_ocr/extract_cells_from_table.py +++ b/table_ocr/extract_cells_from_table.py @@ -16,7 +16,7 @@ def main(f): cell_filename = "{:03d}-{:03d}.png".format(i, j) path = os.path.join(cell_img_dir, cell_filename) cv2.imwrite(path, cell) - print(cell_filename) + print(path) def extract_cell_images_from_table(image):