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"""
This is an advanced PyMuPDF utility for detecting multi-column pages.
It can be used in a shell script, or its main function can be imported and
invoked as descript below.
Features
---------
- Identify text belonging to (a variable number of) columns on the page.
- Text with different background color is handled separately, allowing for
easier treatment of side remarks, comment boxes, etc.
- Uses text block detection capability to identify text blocks and
uses the block bboxes as primary structuring principle.
- Supports ignoring footers via a footer margin parameter.
- Returns re-created text boundary boxes (integer coordinates), sorted ascending
by the top, then by the left coordinates.
Restrictions
-------------
- Only supporting horizontal, left-to-right text
- Returns a list of text boundary boxes - not the text itself. The caller is
expected to extract text from within the returned boxes.
- Text written above images is ignored altogether (option).
- This utility works as expected in most cases. The following situation cannot
be handled correctly:
* overlapping (non-disjoint) text blocks
* image captions are not recognized and are handled like normal text
Usage
------
- As a CLI shell command use
python multi_column.py input.pdf footer_margin
Where footer margin is the height of the bottom stripe to ignore on each page.
This code is intended to be modified according to your need.
- Use in a Python script as follows:
----------------------------------------------------------------------------------
from multi_column import column_boxes
# for each page execute
bboxes = column_boxes(page, footer_margin=50, no_image_text=True)
# bboxes is a list of fitz.IRect objects, that are sort ascending by their y0,
# then x0 coordinates. Their text content can be extracted by all PyMuPDF
# get_text() variants, like for instance the following:
for rect in bboxes:
print(page.get_text(clip=rect, sort=True))
----------------------------------------------------------------------------------
"""
import sys
from magic_pdf.libs.commons import fitz
def column_boxes(page, footer_margin=50, header_margin=50, no_image_text=True):
"""Determine bboxes which wrap a column."""
paths = page.get_drawings()
bboxes = []
# path rectangles
path_rects = []
# image bboxes
img_bboxes = []
# bboxes of non-horizontal text
# avoid when expanding horizontal text boxes
vert_bboxes = []
# compute relevant page area
clip = +page.rect
clip.y1 -= footer_margin # Remove footer area
clip.y0 += header_margin # Remove header area
def can_extend(temp, bb, bboxlist):
"""Determines whether rectangle 'temp' can be extended by 'bb'
without intersecting any of the rectangles contained in 'bboxlist'.
Items of bboxlist may be None if they have been removed.
Returns:
True if 'temp' has no intersections with items of 'bboxlist'.
"""
for b in bboxlist:
if not intersects_bboxes(temp, vert_bboxes) and (
b == None or b == bb or (temp & b).is_empty
):
continue
return False
return True
def in_bbox(bb, bboxes):
"""Return 1-based number if a bbox contains bb, else return 0."""
for i, bbox in enumerate(bboxes):
if bb in bbox:
return i + 1
return 0
def intersects_bboxes(bb, bboxes):
"""Return True if a bbox intersects bb, else return False."""
for bbox in bboxes:
if not (bb & bbox).is_empty:
return True
return False
def extend_right(bboxes, width, path_bboxes, vert_bboxes, img_bboxes):
"""Extend a bbox to the right page border.
Whenever there is no text to the right of a bbox, enlarge it up
to the right page border.
Args:
bboxes: (list[IRect]) bboxes to check
width: (int) page width
path_bboxes: (list[IRect]) bboxes with a background color
vert_bboxes: (list[IRect]) bboxes with vertical text
img_bboxes: (list[IRect]) bboxes of images
Returns:
Potentially modified bboxes.
"""
for i, bb in enumerate(bboxes):
# do not extend text with background color
if in_bbox(bb, path_bboxes):
continue
# do not extend text in images
if in_bbox(bb, img_bboxes):
continue
# temp extends bb to the right page border
temp = +bb
temp.x1 = width
# do not cut through colored background or images
if intersects_bboxes(temp, path_bboxes + vert_bboxes + img_bboxes):
continue
# also, do not intersect other text bboxes
check = can_extend(temp, bb, bboxes)
if check:
bboxes[i] = temp # replace with enlarged bbox
return [b for b in bboxes if b != None]
def clean_nblocks(nblocks):
"""Do some elementary cleaning."""
# 1. remove any duplicate blocks.
blen = len(nblocks)
if blen < 2:
return nblocks
start = blen - 1
for i in range(start, -1, -1):
bb1 = nblocks[i]
bb0 = nblocks[i - 1]
if bb0 == bb1:
del nblocks[i]
# 2. repair sequence in special cases:
# consecutive bboxes with almost same bottom value are sorted ascending
# by x-coordinate.
y1 = nblocks[0].y1 # first bottom coordinate
i0 = 0 # its index
i1 = -1 # index of last bbox with same bottom
# Iterate over bboxes, identifying segments with approx. same bottom value.
# Replace every segment by its sorted version.
for i in range(1, len(nblocks)):
b1 = nblocks[i]
if abs(b1.y1 - y1) > 10: # different bottom
if i1 > i0: # segment length > 1? Sort it!
nblocks[i0 : i1 + 1] = sorted(
nblocks[i0 : i1 + 1], key=lambda b: b.x0
)
y1 = b1.y1 # store new bottom value
i0 = i # store its start index
i1 = i # store current index
if i1 > i0: # segment waiting to be sorted
nblocks[i0 : i1 + 1] = sorted(nblocks[i0 : i1 + 1], key=lambda b: b.x0)
return nblocks
# extract vector graphics
for p in paths:
path_rects.append(p["rect"].irect)
path_bboxes = path_rects
# sort path bboxes by ascending top, then left coordinates
path_bboxes.sort(key=lambda b: (b.y0, b.x0))
# bboxes of images on page, no need to sort them
for item in page.get_images():
img_bboxes.extend(page.get_image_rects(item[0]))
# blocks of text on page
blocks = page.get_text(
"dict",
flags=fitz.TEXTFLAGS_TEXT,
clip=clip,
)["blocks"]
# Make block rectangles, ignoring non-horizontal text
for b in blocks:
bbox = fitz.IRect(b["bbox"]) # bbox of the block
# ignore text written upon images
if no_image_text and in_bbox(bbox, img_bboxes):
continue
# confirm first line to be horizontal
line0 = b["lines"][0] # get first line
if line0["dir"] != (1, 0): # only accept horizontal text
vert_bboxes.append(bbox)
continue
srect = fitz.EMPTY_IRECT()
for line in b["lines"]:
lbbox = fitz.IRect(line["bbox"])
text = "".join([s["text"].strip() for s in line["spans"]])
if len(text) > 1:
srect |= lbbox
bbox = +srect
if not bbox.is_empty:
bboxes.append(bbox)
# Sort text bboxes by ascending background, top, then left coordinates
bboxes.sort(key=lambda k: (in_bbox(k, path_bboxes), k.y0, k.x0))
# Extend bboxes to the right where possible
bboxes = extend_right(
bboxes, int(page.rect.width), path_bboxes, vert_bboxes, img_bboxes
)
# immediately return of no text found
if bboxes == []:
return []
# --------------------------------------------------------------------
# Join bboxes to establish some column structure
# --------------------------------------------------------------------
# the final block bboxes on page
nblocks = [bboxes[0]] # pre-fill with first bbox
bboxes = bboxes[1:] # remaining old bboxes
for i, bb in enumerate(bboxes): # iterate old bboxes
check = False # indicates unwanted joins
# check if bb can extend one of the new blocks
for j in range(len(nblocks)):
nbb = nblocks[j] # a new block
# never join across columns
if bb == None or nbb.x1 < bb.x0 or bb.x1 < nbb.x0:
continue
# never join across different background colors
if in_bbox(nbb, path_bboxes) != in_bbox(bb, path_bboxes):
continue
temp = bb | nbb # temporary extension of new block
check = can_extend(temp, nbb, nblocks)
if check == True:
break
if not check: # bb cannot be used to extend any of the new bboxes
nblocks.append(bb) # so add it to the list
j = len(nblocks) - 1 # index of it
temp = nblocks[j] # new bbox added
# check if some remaining bbox is contained in temp
check = can_extend(temp, bb, bboxes)
if check == False:
nblocks.append(bb)
else:
nblocks[j] = temp
bboxes[i] = None
# do some elementary cleaning
nblocks = clean_nblocks(nblocks)
# return identified text bboxes
return nblocks
if __name__ == "__main__":
"""Only for debugging purposes, currently.
Draw red borders around the returned text bboxes and insert
the bbox number.
Then save the file under the name "input-blocks.pdf".
"""
# get the file name
filename = sys.argv[1]
# check if footer margin is given
if len(sys.argv) > 2:
footer_margin = int(sys.argv[2])
else: # use default vaue
footer_margin = 50
# check if header margin is given
if len(sys.argv) > 3:
header_margin = int(sys.argv[3])
else: # use default vaue
header_margin = 50
# open document
doc = fitz.open(filename)
# iterate over the pages
for page in doc:
# remove any geometry issues
page.wrap_contents()
# get the text bboxes
bboxes = column_boxes(page, footer_margin=footer_margin, header_margin=header_margin)
# prepare a canvas to draw rectangles and text
shape = page.new_shape()
# iterate over the bboxes
for i, rect in enumerate(bboxes):
shape.draw_rect(rect) # draw a border
# write sequence number
shape.insert_text(rect.tl + (5, 15), str(i), color=fitz.pdfcolor["red"])
# finish drawing / text with color red
shape.finish(color=fitz.pdfcolor["red"])
shape.commit() # store to the page
# save document with text bboxes
doc.ez_save(filename.replace(".pdf", "-blocks.pdf")) |