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hocr: simplify some math expressions and add comments

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This commit is contained in:
James R. Barlow 2018-03-14 17:05:40 -07:00
parent 0089a84c94
commit a614fa3400
1 changed files with 19 additions and 7 deletions
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26
ocrmypdf/hocrtransform.py
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@ -227,29 +227,38 @@ class HocrTransform():
line_box = self.pt_from_pixel(pxl_line_coords)
line_height = line_box.y2 - line_box.y1
slope, intercept = self.baseline(line)
slope, pxl_intercept = self.baseline(line)
if abs(slope) < 0.005:
slope = 0.0
angle = atan(slope)
cos_a, sin_a = cos(angle), sin(angle)
text = pdf.beginText()
fontsize = line_height - abs(intercept / self.dpi * inch)
intercept = pxl_intercept / self.dpi * inch
# Don't allow the font to break out of the bounding box. Division by
# cos_a accounts for extra clearance between the glyph's vertical axis
# on a sloped baseline and the edge of the bounding box.
fontsize = (line_height - abs(intercept)) / cos_a
text.setFont(fontname, fontsize)
if invisibleText:
text.setTextRenderMode(3) # Invisible (indicates OCR text)
baseline_y1 = self.height - (line_box.y2 + intercept / self.dpi * inch)
# Intercept is normally negative, so this places it above the bottom
# of the line box
baseline_y2 = self.height - (line_box.y2 + intercept)
if showBoundingboxes:
# draw the baseline in magenta, dashed
pdf.setDash()
pdf.setStrokeColorRGB(0.95, 0.65, 0.95)
pdf.setLineWidth(0.5)
# negate slope because it is defined as a rise/run in pixel
# coordinates and page coordinates have the y axis flipped
pdf.line(line_box.x1,
baseline_y1,
baseline_y2,
line_box.x2,
self.polyval((-slope, baseline_y1),
self.polyval((-slope, baseline_y2),
line_box.x2 - line_box.x1))
# light green for bounding box of word/line
pdf.setDash(6, 3)
@ -257,7 +266,7 @@ class HocrTransform():
text.setTextTransform(
cos_a, -sin_a, sin_a, cos_a,
line_box.x1, self.height - line_box.y2
line_box.x1, baseline_y2
)
pdf.setFillColorRGB(0, 0, 0) # text in black
@ -305,9 +314,12 @@ class HocrTransform():
# "text line" means whatever reportlab defines it as. Do not use
# use .getCursor(), since moveCursor() rather unintuitively plans
# its moves relative to .getStartOfLine().
# For skewed lines, in the text transform we set up a rotated
# coordinate system, so we don't have to account for the
# incremental offset. Surprisingly most PDF viewers can handle this.
cursor = text.getStartOfLine()
dx = box.x1 - cursor[0]
dy = (self.height - line_box.y2 + intercept / self.dpi * inch) - cursor[1]
dy = baseline_y2 - cursor[1]
text.moveCursor(dx, dy)
text.setHorizScale(100 * box_width / font_width)