eynollah/docs/usage.md

# Usage documentation
The command-line interface can be called like this:

```sh
eynollah \
  [GENERIC_OPTIONS] \
  layout \
  -i <single image file> | -di <directory containing image files> \
  -o <output directory> \
  [LAYOUT_OPTIONS]
```

## Generic options
Pass any of the following options:

| **option**                                        | **description**                                                 |
|---------------------------------------------------|:----------------------------------------------------------------|
| -m <directory containing model files>             | override default directory `$PWD/models_eynollah`               |
| -mv <model category> <model variant> <model path> | override specific models, e.g. `region_1_2 '' /path/to/my.onnx` |
| -D <device specifier>                             | allocate models to GPUs, e.g. `col*:CPU,page:GPU1,*:GPU0`       |
| -l <log level>                                    | override default `INFO` log level e.g. `DEBUG`                  |

## Processing options
The following options can be used to further control layout analysis:

| **option**        | **description**                                                                |
|-------------------|:-------------------------------------------------------------------------------|
| `-fl`             | full layout analysis including all steps and segmentation classes (recommended)|
| `-tab`            | apply table detection                                                          |
| `-ae`             | apply enhancement (the resulting image is saved to the output directory)       |
| `-as`             | apply scaling                                                                  |
| `-cl`             | apply contour detection for curved text lines, deskewing regions independently |
| `-ib`             | apply binarization (the resulting image is saved to the output directory)      |
| `-ep`             | enable plotting (MUST always be used with `-sl`, `-sd`, `-sa`, `-si` or `-ae`) |
| `-ho`             | ignore headers for reading order dectection                                    |
| `-si <directory>` | save image regions detected to this directory                                  |
| `-sd <directory>` | save deskewed image to this directory                                          |
| `-sl <directory>` | save layout prediction as plot to this directory                               |
| `-sp <directory>` | save cropped page image to this directory                                      |
| `-sa <directory>` | save all (plot, enhanced/binary image, layout) to this directory               |
| `-thart`          | confidence threshold of artifical boundary class during textline detection     |
| `-tharl`          | confidence threshold of artifical boundary class during region detection       |
| `-ncu`            | upper limit of columns in document image                                       |
| `-ncl`            | lower limit of columns in document image                                       |
| `-slro`           | skip layout detection and reading order                                        |
| `-romb`           | apply machine based reading order detection                                    |
| `-ipe`            | ignore page extraction                                                         |
| `-j`              | number of CPU jobs to run parallel (useful with -di)                           |
| `-H`              | when to halt if some jobs fail, e.g. `0.1` for 10% or `3` for 3 pages          |

If no option is set, the tool performs detection of main regions (background, text, images, separators and marginals).

### `--full-layout` vs shallow

Here are the differences in segment types detected:

|                          | `-fl` | without |
|--------------------------|-------|---------|
| reading order            | x     | x       |
| header regions           | x     | -       |
| text regions             | x     | x       |
| text regions / textlines | x     | x       |
| drop-capitals            | x     | -       |
| marginals                | x     | x       |
| marginals / textlines    | x     | x       |
| image regions            | x     | x       |

(Note: No marginals are detected for pages with 3 columns or more.)

## Use as OCR-D processor
Eynollah ships with a CLI interface to be used as [OCR-D](https://ocr-d.de) processor that is described in 
[`ocrd-tool.json`](https://github.com/qurator-spk/eynollah/tree/main/src/eynollah/ocrd-tool.json). 

The source image file group with (preferably) RGB images should be used as input for Eynollah like this:

```
ocrd-eynollah-segment -I OCR-D-IMG -O SEG-LINE -P full_layout true
```
    
Any image referenced by `@imageFilename` in PAGE-XML is passed on directly to Eynollah as a processor, so that e.g.

```
ocrd-eynollah-segment -I OCR-D-IMG-BIN -O SEG-LINE -P full_layout true
```
    
uses the original (RGB) image despite any binarization that may have occured in previous OCR-D processing steps.

## Use with Docker
TODO

## Hints
* The best output quality is produced when RGB images are used as input rather than greyscale or binarized images.
* If none of the parameters is set to `true`, the tool will perform a layout detection of main regions (background, 
text, images, separators and marginals). An advantage of this tool is that it tries to extract main text regions 
separately as much as possible.
* If you set `-ae` (**a**llow image **e**nhancement) parameter to `true`, the tool will first check the ppi 
(pixel-per-inch) of the image and when it is less than 300, the tool will resize it and only then image enhancement will 
occur. Image enhancement can also take place without this option, but by setting this option to `true`, the layout xml 
data (e.g. coordinates) will be based on the resized and enhanced image instead of the original image.
* For some documents, while the quality is good, their scale is very large, and the performance of tool decreases. In 
such cases you can set `-as` (**a**llow **s**caling) to `true`. With this option enabled, the tool will try to rescale 
the image and only then the layout detection process will begin.
* If you care about drop capitals (initials) and headings, you can set `-fl` (**f**ull **l**ayout) to `true`. With this 
setting, the tool can currently distinguish 7 document layout classes/elements.
* In cases where the document includes curved headers or curved lines, rectangular bounding boxes for textlines will not 
be a great option. In such cases it is strongly recommended setting the flag `-cl` (**c**urved **l**ines) to `true` to 
find contours of curved lines instead of rectangular bounding boxes. Be advised that enabling this option increases the 
processing time of the tool.
* To crop and save image regions inside the document, set the parameter `-si` (**s**ave **i**mages) to true and provide 
a directory path to store the extracted images.
* To extract only images from a document, set the parameter `-eoi` (**e**xtract **o**nly **i**mages). Choosing this 
option disables any other processing. To save the cropped images add `-ep` and `-si`.