> ## Documentation Index
> Fetch the complete documentation index at: https://sensible.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Preprocessors

Use the following preprocessors to clean up your documents before extracting structured data. Preprocessors execute in the order you define them in an array.

| Preprocessor                                                        | Image                                                                                                                              | Notes                                                                                                                                                                                               |
| ------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| **[Deskew](/senseml-reference/preprocessors/deskew)**               | ![Click to enlarge](https://mintlify.s3-us-west-1.amazonaws.com/sensible/assets/v0/images/screenshots/thumbnail_deskew.png)        | Corrects the alignment of documents that are skewed, for example as a result of being photographed at an angle instead of straight on.                                                              |
| **[Ligature](/senseml-reference/preprocessors/ligature)**           | ![Click to enlarge](https://mintlify.s3-us-west-1.amazonaws.com/sensible/assets/v0/images/screenshots/thumbnail_ligature.png)      | Intelligently replaces Unicode ligatures in a text extraction.                                                                                                                                      |
| **[Merge Lines](/senseml-reference/preprocessors/merge-lines)**     | ![Click to enlarge](https://mintlify.s3-us-west-1.amazonaws.com/sensible/assets/v0/images/screenshots/merge_lines_oversplit_1.png) | Corrects oversplit lines.                                                                                                                                                                           |
| **[NLP](/senseml-reference/preprocessors/nlp)**                     | Advanced prompt configuration for each large language model (LLM)-based method in a config.                                        |                                                                                                                                                                                                     |
| **[OCR](/senseml-reference/preprocessors/ocr-preprocessor)**        | ![Click to enlarge](https://mintlify.s3-us-west-1.amazonaws.com/sensible/assets/v0/images/screenshots/thumbnail_ocr.png)           | Selectively OCRs pages in documents containing a mix of digitally generated text and text images (such as scanned text). If the whole PDF is a scan, you don't need to configure this preprocessor. |
| **[Page Range](/senseml-reference/preprocessors/page-range)**       | Ignores pages outside the start page and end page.                                                                                 |                                                                                                                                                                                                     |
| **[Remove Header](/senseml-reference/preprocessors/remove-header)** | ![Click to enlarge](https://mintlify.s3-us-west-1.amazonaws.com/sensible/assets/v0/images/screenshots/remove_header_1.png)         | Removes repeating elements at the top of the page. Ignores header elements that overlap with the page's main body.                                                                                  |
| **[Remove Footer](/senseml-reference/preprocessors/remove-footer)** | ![Click to enlarge](https://mintlify.s3-us-west-1.amazonaws.com/sensible/assets/v0/images/screenshots/remove_footer_1.png)         | Removes repeating elements at the bottom of the page. Ignores footer elements that overlap with the page's main body.                                                                               |
| **[Rotate page](/senseml-reference/preprocessors/rotate-page)**     | ![Click to enlarge](https://mintlify.s3-us-west-1.amazonaws.com/sensible/assets/v0/images/screenshots/rotate_page_2.png)           | In most cases, Sensible corrects page rotation automatically. If it doesn't, configure this preprocessor.                                                                                           |
| **[Scale](/senseml-reference/preprocessors/scale)**                 | ![Click to enlarge](https://mintlify.s3-us-west-1.amazonaws.com/sensible/assets/v0/images/screenshots/thumbnail_scale.png)         | Corrects the size of text in documents whose size varies, for example as a result of being scanned or photographed at different scales.                                                             |
| **[Split Lines](/senseml-reference/preprocessors/split-lines)**     | ![Click to enlarge](https://mintlify.s3-us-west-1.amazonaws.com/sensible/assets/v0/images/screenshots/thumbnail_split_lines.png)   | Corrects undersplit lines.                                                                                                                                                                          |