Straighten Chart corrects bowed, curved or wavy grid lines—for example, when a chart has been photographed from a book. It reshapes the chart image so its printed grid aligns with the Markup grid and can be stitched accurately.

This is an optional step after Confirm Size. Use it when the corners and grid size are correct but the printed lines still curve away from the overlay.

Before you begin: The grid corners and row and column counts must be correct. If even one row or column is missing, straightening cannot produce an accurate result. Align the thick overlay lines with the chart's thick printed lines before placing any points; changing the spacing or offsets later resets the points.

The Thick Grid Line Offsets reminder shown before point placement

This reminder appears before you begin. Make the offset adjustments at this point, before investing time in individual straightening points.

Straighten Chart at a Glance

The complete Straighten Chart screen, with the chart in the centre, tool chip on the left and navigation buttons along the bottom

The chart is shown with a red grid overlay and blue straightening points. The tool chip controls the grid spacing and offsets; Apply previews your correction, and Finish saves it.

The Basic Workflow

1. Check the input
Confirm that the outline follows the chart boundary and that the row and column counts are exact. Go back to Confirm Size if anything is wrong.
2. Align the thick grid lines
Use the x5/x10 setting and X/Y offset arrows until the thick overlay lines match the chart's thick printed lines. Do this before placing points.
3. Place and adjust points
Tap grid intersections and move each selected point onto the corresponding printed intersection. Use the magnifier and arrows for precise placement.
4. Apply and review
Choose Apply to straighten the image, then inspect the result. Use Undo and Redo to compare applied versions, or add more control points and apply again.
5. Finish
When the grid aligns throughout the page, choose Finish. Markup saves the adjusted grid and, after confirmation, updates that page in the project's source PDF.

The Tool Chip

Set Up and Review the Grid

The Straighten Chart tool chip, numbered from one to four

  1. Undo and Redo: Step backwards or forwards through corrections that you have applied.
  2. Point spacing: Switch between x10 and x5. Use x10 for broad corrections and x5 when a smaller area needs extra control.
  3. X offset: Move the pattern of thick vertical overlay lines sideways until it matches the chart.
  4. Y offset: Move the pattern of thick horizontal overlay lines up or down until it matches the chart.

Learn the Process

Detailed Guides

1. Prepare the Chart

Learn how to check the corners and counts, choose x5 or x10 spacing, and align the thick grid lines with the X/Y offsets.

Detailed setup guide and screenshots to be added.

2. Place Points in a Reliable Order

A useful starting sequence is: top edge, bottom edge, left edge, right edge, horizontal centre, vertical centre, then the corners and any remaining problem areas. This corrects broad distortion before you spend time on local detail.

See the reliable point-placement method.

3. Refine and Review the Result

Apply the correction and inspect the whole chart. For a sharp bend near a book fold or corner, switch to the x5 layout to gain more control in that area, then place additional points and apply again.

Detailed refinement and results guide with before-and-after screenshots to be added.

Important to Know

  • Correct setup matters more than the number of points. Wrong corners or counts cannot be fixed by adding more straightening points.
  • Start broad, then refine. Align the main edges and centre lines before working on individual corners or local bends.
  • Use x5 only where you need more control. The denser layout is useful around sharp bends, folds and difficult corners.
  • Apply can be repeated. Review each result, add or adjust points, and apply again until the overlay follows the printed grid.

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