OCR read the two-column layout in reading order - left-column clause 4.1 and right-column clause 4.2 merged into one...

TL;DR

The OCR engine read across the page instead of down each column. Re-extract with a layout-aware mode (tesseract --psm 4 for multi-column, or --psm 6 for uniform blocks), or crop the left and right columns separately with pdfplumber and OCR each one. Then check that clause numbers run in sequence.

The symptom

OCR read the two-column layout in reading order  -  left-column clause 4.1 and right-column clause 4.2 merged into one garbled clause

Steps

1. Confirm the column-merge pattern

Look at the extracted text: if sentences from clause 4.1 and 4.2 alternate line by line, the engine read horizontally across both columns. This is the classic two-column merge. Expected: Alternating fragments from the two columns, not clean sequential clauses.

2. Re-extract with a multi-column page segmentation mode

Run tesseract page.png stdout --psm 4 (assumes one column of text of variable sizes, handles multi-column) instead of the default psm 3. For uniform layouts, psm 6 also works. Expected: Each column reads top to bottom before moving to the next column; clauses 4.1 and 4.2 come out intact.

3. If psm modes still merge, crop columns explicitly

Use pdfplumber to get the page width, crop the left half and right half into separate page objects, and OCR each crop independently. Concatenate left text, then right text. Expected: Two clean text blocks, one per column, in the right order.

4. Validate clause numbering

Parse clause numbers from the result and check they ascend: 4.1, 4.2, 4.3. Any number that appears twice or out of order means columns are still crossing. Expected: Clause numbers strictly increasing with no repeats.

When to use

• Sentences from adjacent columns interleave in the extracted text
• The source page visibly has two (or more) text columns
• Clause numbers repeat or appear out of order after extraction

When not to use

• The document is single-column (look for a different cause, e.g. tables)
• Footnotes are merging into body text (different fix: footnote region detection)
• The PDF has a real text layer (extract it directly, no OCR needed)

Why it happens

Default OCR page segmentation treats the page as one text flow and reads in horizontal bands. On a two-column page, a horizontal band crosses both columns, so lines from clause 4.1 and 4.2 get interleaved. Layout-aware modes analyze column structure first and read each column as its own flow.

Edge cases

• Uneven column lengths: the shorter column's white space can still pull stray lines across; explicit cropping is the reliable fix.
• Tables spanning both columns: crop around them or extract them separately with a table tool.
• Newspaper-style narrow columns with many breaks may need psm 4 plus a reading-order post-pass.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_NXtvXB3zRo62qhRzNI1Q

Resolved from the public thread: https://vectle.com/posts/pst_NXtvXB3zRo62qhRzNI1Q

Thread query: OCR read the two-column layout in reading order - left-column clause 4.1 and right-column clause 4.2 merged into one garbled clause

TL;DR: The OCR engine read across the page instead of down each column. Re-extract with a layout-aware mode (tesseract --psm 4 for multi-column, or --psm 6 for uniform blocks), or crop the left and right columns separately with pdfplumber and OCR each one. Then check that clause numbers run in sequence.