#  `deskew`

Automatically detect and correct document skew
## Usage
> pdftl `<input>` `deskew` `[<page_specs>...]` `[max_skew=<val>]` `[dpi=<val>]` `output` `<file>`

## Details
The `deskew` operation automatically detects rotational misalignment (skew)
commonly found in scanned documents and aligns the text horizontally.

### How it works
This operation runs a page-level hybrid vector/raster deskew:
  1. The page is rendered at a low resolution to analyze its layout.
  2. A projection profile variance analysis (Radon-style line search)
     detects the dominant text angle within the specified `max_skew` range.
  3. If the active text region or page size is too small for a high-fidelity line search,
     the page is dynamically re-rendered at a higher resolution (up to 600 DPI) to prevent
     coarse-grain estimation and boundary errors.
  4. The entire page coordinate space is rotated around its visual center
     to correct the alignment.
  5. Vector content, high-resolution image assets, and text rendering remains
     lossless because the coordinate grid itself is rotated.
  6. Clickable hyperlinks, highlights, and annotations are transformed
     automatically to match their new visual locations.

### Parameters
* `max_skew=<val>` (default: 10.0) — The maximum search limit for skew detection,
  in degrees. Restricting this window speeds up analysis and avoids false-positive
  rotations on non-standard layouts.
* `dpi=<val>` (default: 75) — Resolution of the rasterized page used for
  skew analysis. 75 DPI is generally optimal for fast, robust line detection.
* `max_render_dpi=<val>` (default: 600) — Ceiling on the resolution used when
  a small text region is re-rendered for closer analysis. This controls how
  much detail is *captured*; it is independent of `coarse_res`/`fine_res`
  below, which control how much of that captured detail is *analyzed*.
* `coarse_res=<val>` (default: 300) — Target pixel footprint (long edge) used
  for the initial coarse angle search. Lower values are faster but risk
  missing the correct angle's neighborhood on very fine or sparse text.
* `fine_res=<val>` (default: 600) — Target pixel footprint (long edge) used
  for the fine, sub-degree angle search. Higher values improve precision
  (reducing residual jitter of a few tenths of a degree) at the cost of
  slower analysis; lower values trade some precision for speed.
## Examples

> Automatically detect and correct skew on all pages.
```
pdftl in.pdf deskew output out.pdf
```

> Automatically deskew only the even pages, limiting search to 5 degrees.
```
pdftl in.pdf deskew even max_skew=5 output out.pdf
```

> Deskew pages 1 to 3 with a higher analysis resolution of 150 DPI.
```
pdftl in.pdf deskew 1-3 dpi=150 output out.pdf
```

> Prioritize speed over precision by using smaller search footprints.
```
pdftl in.pdf deskew coarse_res=150 fine_res=300 output out.pdf
```


**Tags**: content_modification, geometry

*Source: pdftl.operations.deskew*

*Read online: [https://pdftl.readthedocs.io/en/latest/operations/deskew.html](https://pdftl.readthedocs.io/en/latest/operations/deskew.html)*

*Type: Operation*