Reading the results and planning a deskew

What the angles tell you

Each straightened page is listed with its correction. A positive number means the content was turned counter-clockwise to level it, so the page was leaning clockwise. A negative number means the opposite. Automatic angles are rounded to hundredths of a degree.

The pattern across a batch is worth a look, because it says something about how the pages were scanned:

• Roughly the same angle on every page usually means the feeder's paper guides are set slightly off, so every sheet enters at the same slant. Adjusting the guides helps the next batch.
• Similar angles with opposite signs on odd and even pages is typical of double-sided scanning. A sheet that leans one way seen from the front leans the other way seen from the back.
• Scattered angles on a handful of pages point at sheets that slipped in the feeder, or pages placed by hand on the glass.

Everything on the page turns together

Deskew rotates the page's whole content as one piece. That includes anything earlier tools wrote into the page. The page numbers, headers, footers, watermarks and Bates numbers that EddiesPDF adds are drawn into the page content, and so is text typed in the editor. If you number a crooked scan and straighten it afterwards, the scan comes out level and the numbers come out crooked.

So straighten first, and add those afterwards with Page numbers, Header & footer, Watermark or Bates numbering. Doing it in that order also helps the measurement itself. A line of perfectly level text added to a tilted scan competes with the scan's own lines and can make the tilt harder to detect.

Files that mix scans and digital pages

A merged document often has a few scanned pages among pages exported from Word or a web browser. You can run Automatic on the whole file. Digital pages are already level, so no angle measures better than leaving them alone, and they're reported as unchanged.

The cost is time, since every page in the range is rendered and measured in turn. If you know only pages 30 to 45 are scans in a 200-page file, a custom range of 30-45 finishes much sooner.

Landscape pages, and pages turned earlier with a rotate tool, are measured the way they appear on screen. The correction goes in the direction you see, whichever way the page is stored inside the file.

Pages that were cropped earlier

The rotation turns around the centre of the page's visible area. If the page was cropped before, the content hidden outside the crop turns with everything else, and near the corners a little of it can swing into view: a strip of scanner lid, or the edge of the facing page in a book scan. At one or two degrees that's only a thin wedge, but it's a good reason to run Crop PDF after deskewing rather than before. A crop set on a level page can also be tighter.

Manual angle works the same way on any page: it turns the content by the amount you type, on top of whatever rotation is already there. It never sets an absolute angle, so a page that was straightened once needs only the small remaining difference.