Applies to: Straightening scanned images; this can resample pixels and change the crop.
Align the paper guides or flatbed edge, scan one difficult page, then enable automatic deskew in the scanner or PDF application. Compare the corrected page with the original at high zoom and confirm that headers, footers, stamps, and handwritten notes remain intact.
Fix the capture problem first
Skew often begins with loose feeder guides, curled pages, mixed paper sizes, folded corners, or a document placed away from the flatbed reference edge. Software can rotate the image, but it cannot restore detail that was never captured.
Square the stack, remove clips and folds, adjust guides so they touch the paper without binding it, and separate sheets that cling together. On a flatbed, align the page with the marked corner.
Apply deskew to a test page
Deskew estimates the angle of text lines or page edges and rotates the scanned image by a small amount. It works best when the page has clear text or a strong rectangular boundary.
- Keep an untouched source scan.
- Choose the most crooked representative page.
- Enable Deskew or Straighten in the scan or enhancement settings.
- Preview the crop after correction.
- Inspect all four corners and small edge notes.
- Apply the setting to the batch only after the test passes.
Watch for crop and interpolation
Rotating a rectangular image creates empty triangles near the edges, so software may crop inward or add a background color. A tight original crop can lose page numbers, punched-edge notes, signatures, or seals.
The rotation also resamples pixels. For ordinary text the difference may be minor, but preservation masters should follow the responsible archive’s rules rather than applying undocumented cleanup.
Verify OCR after straightening
Straighter lines often help OCR, but recognition should still be checked. Search for words near the top, center, and bottom of the page and verify names, dates, decimal points, and page numbers visually.
If automatic deskew produces inconsistent angles, turn it off and rescan with better physical alignment. Strong graphics, decorative borders, or mostly blank pages can confuse the angle detector.
Compare all four corners before accepting automatic cleanup
Choose a page with a visible page number and an annotation near an edge. Save a copy before applying deskew. Check that the corrected output keeps both marks, then inspect the other two corners and any stamps. A straighter text block is not an improvement if it removes evidence at the edge.
If repeated pages rotate in inconsistent directions, disable automatic correction and improve the capture alignment. Sparse text, a strong decorative border or a photograph can give the angle detector a misleading reference.
Sources and further reading
Vendor instructions and background references are linked below. Worked examples are our explanatory calculations, not vendor performance claims. Check the instructions for your current software and device.
Report a correction with this page’s title and the step or result that needs attention.