ocr/README.md

# OCR

## Build image

1. Clone this repository and navigate into it:
```
git clone https://gitlab.ub.uni-bielefeld.de/sfb1288inf/ocr.git && cd ocr
```

2. Build image:
```
docker build -t sfb1288inf/ocr:latest .
```

Alternatively build from the GitLab repository without cloning:

1. Build image:
```
docker build -t sfb1288inf/ocr:latest https://gitlab.ub.uni-bielefeld.de/sfb1288inf/ocr.git
```

## Download prebuilt image

The GitLab registry provides a prebuilt image. It is automatically created, utilizing the conquaire build servers.

1. Download image:
```
docker pull gitlab.ub.uni-bielefeld.de:4567/sfb1288inf/ocr:latest
```

## Run

1. Create input and output directories for the OCR software:
```
mkdir -p /<mydatalocation>/files_for_ocr /<mydatalocation>/files_from_ocr
```

2. Place your files inside the `/<mydatalocation>/files_for_ocr` directory. Files can either be PDF (.pdf) or multipage TIFF (.tiff, .tif) files. Files should all contain text of the same language.

3. Start the OCR process.
```
docker run \
    --rm \
    -it \
    -u $(id -u $USER):$(id -g $USER) \
    -v /<mydatalocation>/files_for_ocr:/input \
    -v /<mydatalocation>/files_from_ocr:/output \
    sfb1288inf/ocr:latest \
        -i /input \
        -l <languagecode> \
        -o /output
```
The arguments below `sfb1288inf/ocr:latest` are described in the [OCR arguments](#ocr-arguments) part.

If you want to use the prebuilt image, replace `sfb1288inf/ocr:latest` with `gitlab.ub.uni-bielefeld.de:4567/sfb1288inf/ocr:latest`.

4. Check your results in the `/<mydatalocation>/files_from_ocr` directory.

### OCR arguments

`-l languagecode`
* Tells tesseract which language will be used.
* options = deu (German), deu_frak (German Fraktur), eng (English), enm (Middle englisch), fra (French), frm (Middle french), ita (Italian), por (Portuguese), spa (Spanish)
* required = True

`--keep-intermediates`
* If set, all intermediate files created during the OCR process will be
kept.
* default = False
* required = False

`--nCores corenumber`
* Sets the number of CPU cores being used during the OCR process.
* default = min(4, multiprocessing.cpu_count())
* required = False

`--skip-binarisation`
* Used to skip binarization with ocropus. If skipped, only the tesseract binarization is used.
* default = False

Example with all arguments used:
```
docker run \
    --rm \
    -it \
    -u $(id -u $USER):$(id -g $USER) \
    -v "$HOME"/ocr/files_for_ocr:/input \
    -v "$HOME"/ocr/files_from_ocr:/output \
    sfb1288inf/ocr:latest \
        -i /input \
        -l eng \
        -o /output \
        --keep_intermediates \
        --nCores 8 \
        --skip-binarisation
```

# Additional language models for OCR
Additional language models can be easily installed. Just add them analogical to the existing models to the `Dockerfile`.

The standard language models for various languages can be found under https://github.com/tesseract-ocr/tessdata. Click on one of the languages and copy the link from the download button. The URL for Afrikaans (afr) would be for example https://github.com/tesseract-ocr/tessdata/raw/4.00/afr.traineddata.

The more accurate but slower language models can be found under https://github.com/tesseract-ocr/tessdata_best. Click on one of the languages and copy the link from the download button. The URL for Afrikaans (afr) would be for example https://github.com/tesseract-ocr/tessdata_best/raw/master/afr.traineddata.

Language models for fraktur fonts can also be found in the standard tessdata repository https://github.com/tesseract-ocr/tessdata.

The `Dockerfile` section for the language models with added language support for Afrikaans would look like this:

```
RUN echo "deb https://notesalexp.org/tesseract-ocr/stretch/ stretch main" >> /etc/apt/sources.list && \
    wget -O - https://notesalexp.org/debian/alexp_key.asc | apt-key add - && \
    apt-get update && \
    apt-get install -y --no-install-recommends tesseract-ocr && \
    wget -nv https://github.com/tesseract-ocr/tessdata_best/raw/master/afr.traineddata -P /usr/share/tesseract-ocr/4.00/tessdata \
    wget -nv https://github.com/tesseract-ocr/tessdata_best/raw/master/deu.traineddata -P /usr/share/tesseract-ocr/4.00/tessdata && \
    wget -nv https://github.com/tesseract-ocr/tessdata/raw/master/deu_frak.traineddata -P /usr/share/tesseract-ocr/4.00/tessdata && \
    wget -nv https://github.com/tesseract-ocr/tessdata_best/raw/master/eng.traineddata -P /usr/share/tesseract-ocr/4.00/tessdata && \
    wget -nv https://github.com/tesseract-ocr/tessdata_best/raw/master/enm.traineddata -P /usr/share/tesseract-ocr/4.00/tessdata && \
    wget -nv https://github.com/tesseract-ocr/tessdata_best/raw/master/fra.traineddata -P /usr/share/tesseract-ocr/4.00/tessdata && \
    wget -nv https://github.com/tesseract-ocr/tessdata_best/raw/master/frm.traineddata -P /usr/share/tesseract-ocr/4.00/tessdata && \
    wget -nv https://github.com/tesseract-ocr/tessdata_best/raw/master/ita.traineddata -P /usr/share/tesseract-ocr/4.00/tessdata && \
    wget -nv https://github.com/tesseract-ocr/tessdata_best/raw/master/por.traineddata -P /usr/share/tesseract-ocr/4.00/tessdata && \
    wget -nv https://github.com/tesseract-ocr/tessdata_best/raw/master/spa.traineddata -P /usr/share/tesseract-ocr/4.00/tessdata
```