ocrd-tool.json
Tools MUST be described in a file ocrd-tool.json
in the root of the repository.
It must contain a JSON object adhering to the ocrd-tool JSON Schema.
In particular, every tool provided must be described in an array item under the
tools
key. These definitions drive the CLI and the web
services.
To validate a ocrd-tool.json
file, use ocrd ocrd-tool /path/to/ocrd-tool.json validate
.
File parameters
To mark a parameter as expecting the address of a file, it MUST declare the
content-type
property as a valid media
type.
Optionally, workflow processors can be notified that this file is potentially
large and static (e.g. a fixed dataset or a precomputed model) and should be cached
indefinitely after download by setting the cacheable
property to true
.
The filename itself, i.e. the concrete value <fpath>
of a file parameter,
should be resolved in the following way (with <cwd>
representing the current
working directory, and <mod>
representing the distribution directory of the module):
- If
<fpath>
is anhttp
/https
URL: Download to a temporary directory (ifcacheable==False
) or a semi-temporary cache directory (ifcacheable==True
) - If
<fpath>
is an absolute path: Use as-is. - If
<fpath>
is a relative path (with or without directory components): Try resolving via the following directories, and return the first one found if any, otherwise abort with an error message stating so:<cwd>/<fpath>
(Note that the file is expected to be directly under<cwd>
, not in a subdirectory)- If an environment variable is defined that has the name of the processor in
upper-case and with
-
replaced with-
and followed by_PATH
(e.g. for a processorocrd-dummy
, the variable would need to be calledOCRD_DUMMY_PATH
):- Split the variable value at
:
and try to resolve by appending<fpath>
to each token and return the first found file if any
- Split the variable value at
$XDG_DATA_HOME/ocrd-resources/<name-of-processor>/<fpath>
(with$HOME/.local/share
instead of$XDG_DATA_HOME
if unset)/usr/local/share/ocrd-resources/<name-of-processor>/<fpath>
<mod>/<fpath>
(Note that the file is expected to be directly under<mod>
, not in a subdirectory)
The path of the <mod>
directory is implementation specific and allows modules
to distribute small resources along with the code, i.e. pre-installed files like
presets.
Input / Output file groups
Tools should define the names of both expected input and produced output file
groups as a list of USE
attributes of mets:fileGrp
elements. If more than
one file group is expected or produced, this should be explained in the
description of the tool.
NOTE: Both input and output file groups can be overridden at
runtime. Tools must therefore ensure not to
hardcode file group names. When multiple groups are expected, the order of the
override reflects the order in which they are defined in the ocrd-tool.json
.
Definition
type: object
description: Schema for tools by OCR-D MP
required:
- version
- git_url
- tools
additionalProperties: false
properties:
version:
description: "Version of the tool, expressed as MAJOR.MINOR.PATCH."
type: string
pattern: '^[0-9]+\.[0-9]+\.[0-9]+$'
git_url:
description: Github/Gitlab URL
type: string
format: url
dockerhub:
description: DockerHub image
type: string
tools:
type: object
additionalProperties: false
patternProperties:
'ocrd-.*':
type: object
additionalProperties: false
required:
- description
- steps
- executable
- categories
- input_file_grp
# Not required because not all processors produce output files
# - output_file_grp
properties:
executable:
description: The name of the CLI executable in $PATH
type: string
input_file_grp:
description: Input fileGrp@USE this tool expects by default
type: array
items:
type: string
# pattern: '^OCR-D-[A-Z0-9-]+$'
output_file_grp:
description: Output fileGrp@USE this tool produces by default
type: array
items:
type: string
# pattern: '^OCR-D-[A-Z0-9-]+$'
parameters:
description: Object describing the parameters of a tool. Keys are parameter names, values sub-schemas.
type: object
patternProperties:
".*":
type: object
additionalProperties: false
required:
- description
- type
# also either 'default' or 'required'
properties:
type:
type: string
description: Data type of this parameter
enum:
- string
- number
- boolean
- object
- array
format:
description: Subtype, such as `float` for type `number` or `uri` for type `string`.
description:
description: Concise description of syntax and semantics of this parameter
items:
type: object
description: describe the items of an array further
minimum:
type: number
description: Minimum value for number parameters, including the minimum
maximum:
type: number
description: Maximum value for number parameters, including the maximum
exclusiveMinimum:
type: number
description: Minimum value for number parameters, excluding the minimum
exclusiveMaximum:
type: number
description: Maximum value for number parameters, excluding the maximum
multipleOf:
type: number
description: For number values, those values must be multiple of this number
properties:
type: object
description: Describe the properties of an object value
additionalProperties:
type: boolean
description: Whether an object value may contain properties not explicitly defined
required:
type: boolean
description: Whether this parameter is required
default:
description: Default value when not provided by the user
enum:
type: array
description: List the allowed values if a fixed list.
content-type:
type: string
default: 'application/octet-stream'
description: >
The media type of resources this processor expects for
this parameter. Most processors use files for resources
(e.g. `*.traineddata` for `ocrd-tesserocr-recognize`)
while others use directories of files (e.g. `default` for
`ocrd-eynollah-segment`). If a parameter requires
directories, it must set `content-type` to
`text/directory`.
cacheable:
type: boolean
description: "If parameter is reference to file: Whether the file should be cached, e.g. because it is large and won't change."
default: false
description:
description: Concise description what the tool does
categories:
description: Tools belong to this categories, representing modules within the OCR-D project structure
type: array
items:
type: string
enum:
- Image preprocessing
- Layout analysis
- Text recognition and optimization
- Model training
- Long-term preservation
- Quality assurance
steps:
description: This tool can be used at these steps in the OCR-D functional model
type: array
items:
type: string
enum:
- preprocessing/characterization
- preprocessing/optimization
- preprocessing/optimization/cropping
- preprocessing/optimization/deskewing
- preprocessing/optimization/despeckling
- preprocessing/optimization/dewarping
- preprocessing/optimization/binarization
- preprocessing/optimization/grayscale_normalization
- recognition/text-recognition
- recognition/font-identification
- recognition/post-correction
- layout/segmentation
- layout/segmentation/text-nontext
- layout/segmentation/region
- layout/segmentation/line
- layout/segmentation/word
- layout/segmentation/classification
- layout/analysis
resource_locations:
type: array
description: The locations in the filesystem this processor supports for resource lookup
default: ['data', 'cwd', 'system', 'module']
items:
type: string
enum: ['data', 'cwd', 'system', 'module']
resources:
type: array
description: Resources for this processor
items:
type: object
additionalProperties: false
required:
- url
- description
- name
- size
properties:
url:
type: string
description: URLs of all components of this resource
description:
type: string
description: A description of the resource
name:
type: string
description: Name to store the resource as
type:
type: string
enum: ['file', 'directory', 'archive']
default: file
description: Type of the URL
parameter_usage:
type: string
description: Defines how the parameter is to be used
enum: ['as-is', 'without-extension']
default: 'as-is'
path_in_archive:
type: string
description: if type is archive, the resource is at this location in the archive
default: '.'
version_range:
type: string
description: Range of supported versions, syntax like in PEP 440
default: '>= 0.0.1'
size:
type: number
description: Size of the resource in bytes
Example
This is from the ocrd_tesserocr project:
{
"version": "0.10.0",
"git_url": "https://github.com/OCR-D/ocrd_tesserocr",
"dockerhub": "ocrd/tesserocr",
"tools": {
"ocrd-tesserocr-deskew": {
"executable": "ocrd-tesserocr-deskew",
"categories": ["Image preprocessing"],
"description": "Detect script, orientation and skew angle for pages or regions",
"input_file_grp": [
"OCR-D-IMG",
"OCR-D-SEG-BLOCK"
],
"output_file_grp": [
"OCR-D-DESKEW-BLOCK"
],
"steps": ["preprocessing/optimization/deskewing"],
"parameters": {
"dpi": {
"type": "number",
"format": "float",
"description": "pixel density in dots per inch (overrides any meta-data in the images); disabled when negative",
"default": 0
},
"operation_level": {
"type": "string",
"enum": ["page","region"],
"default": "region",
"description": "PAGE XML hierarchy level to operate on"
},
"min_orientation_confidence": {
"type": "number",
"format": "float",
"default": 1.5,
"description": "Minimum confidence score to apply orientation as detected by OSD"
}
}
},
"ocrd-tesserocr-fontshape": {
"executable": "ocrd-tesserocr-fontshape",
"categories": ["Text recognition and optimization"],
"description": "Recognize font shapes (family/monospace/bold/italic) and size in segmented words with Tesseract (using annotated derived images, or masking and cropping images from coordinate polygons), annotating TextStyle",
"input_file_grp": [
"OCR-D-SEG-WORD",
"OCR-D-OCR"
],
"output_file_grp": [
"OCR-D-OCR-STYLE"
],
"steps": ["recognition/font-identification"],
"parameters": {
"dpi": {
"type": "number",
"format": "float",
"description": "pixel density in dots per inch (overrides any meta-data in the images); disabled when negative",
"default": 0
},
"padding": {
"type": "number",
"format": "integer",
"default": 0,
"description": "Number of background-filled pixels to add around the word image (i.e. the annotated AlternativeImage if it exists or the higher-level image cropped to the bounding box and masked by the polygon otherwise) on each side before recognition."
},
"model": {
"type": "string",
"default": "osd",
"description": "tessdata model to apply (an ISO 639-3 language specification or some other basename, e.g. deu-frak or osd); must be an old (pre-LSTM) model"
}
}
},
"ocrd-tesserocr-recognize": {
"executable": "ocrd-tesserocr-recognize",
"categories": ["Text recognition and optimization"],
"description": "Segment and/or recognize text with Tesseract (using annotated derived images, or masking and cropping images from coordinate polygons) on any level of the PAGE hierarchy.",
"input_file_grp": [
"OCR-D-SEG-PAGE",
"OCR-D-SEG-REGION",
"OCR-D-SEG-TABLE",
"OCR-D-SEG-LINE",
"OCR-D-SEG-WORD"
],
"output_file_grp": [
"OCR-D-SEG-REGION",
"OCR-D-SEG-TABLE",
"OCR-D-SEG-LINE",
"OCR-D-SEG-WORD",
"OCR-D-SEG-GLYPH",
"OCR-D-OCR-TESS"
],
"steps": [
"layout/segmentation/region",
"layout/segmentation/line",
"recognition/text-recognition"
],
"parameters": {
"dpi": {
"type": "number",
"format": "float",
"description": "pixel density in dots per inch (overrides any meta-data in the images); disabled when negative",
"default": 0
},
"padding": {
"type": "number",
"format": "integer",
"default": 0,
"description": "Extend detected region/cell/line/word rectangles by this many (true) pixels, or extend existing region/line/word images (i.e. the annotated AlternativeImage if it exists or the higher-level image cropped to the bounding box and masked by the polygon otherwise) by this many (background/white) pixels on each side before recognition."
},
"segmentation_level": {
"type": "string",
"enum": ["region", "cell", "line", "word", "glyph", "none"],
"default": "word",
"description": "Highest PAGE XML hierarchy level to remove existing annotation from and detect segments for (before iterating downwards); if ``none``, does not attempt any new segmentation; if ``cell``, starts at table regions, detecting text regions (cells). Ineffective when lower than ``textequiv_level``."
},
"textequiv_level": {
"type": "string",
"enum": ["region", "cell", "line", "word", "glyph", "none"],
"default": "word",
"description": "Lowest PAGE XML hierarchy level to re-use or detect segments for and add the TextEquiv results to (before projecting upwards); if ``none``, adds segmentation down to the glyph level, but does not attempt recognition at all; if ``cell``, stops short before text lines, adding text of text regions inside tables (cells) or on page level only."
},
"overwrite_segments": {
"type": "boolean",
"default": false,
"description": "If ``segmentation_level`` is not none, but an element already contains segments, remove them and segment again. Otherwise use the existing segments of that element."
},
"overwrite_text": {
"type": "boolean",
"default": true,
"description": "If ``textequiv_level`` is not none, but a segment already contains TextEquivs, remove them and replace with recognised text. Otherwise add new text as alternative. (Only the first entry is projected upwards.)"
},
"block_polygons": {
"type": "boolean",
"default": false,
"description": "When detecting regions, annotate polygon coordinates instead of bounding box rectangles."
},
"find_tables": {
"type": "boolean",
"default": true,
"description": "When detecting regions, recognise tables as table regions (Tesseract's ``textord_tabfind_find_tables=1``)."
},
"sparse_text": {
"type": "boolean",
"default": false,
"description": "When detecting regions, use 'sparse text' page segmentation mode (finding as much text as possible in no particular order): only text regions, single lines without vertical or horizontal space."
},
"raw_lines": {
"type": "boolean",
"default": false,
"description": "When detecting lines, do not attempt additional segmentation (baseline+xheight+ascenders/descenders prediction) on line images. Can increase accuracy for certain workflows. Disable when line segments/images may contain components of more than 1 line, or larger gaps/white-spaces."
},
"char_whitelist": {
"type": "string",
"default": "",
"description": "When recognizing text, enumeration of character hypotheses (from the model) to allow exclusively; overruled by blacklist if set."
},
"char_blacklist": {
"type": "string",
"default": "",
"description": "When recognizing text, enumeration of character hypotheses (from the model) to suppress; overruled by unblacklist if set."
},
"char_unblacklist": {
"type": "string",
"default": "",
"description": "When recognizing text, enumeration of character hypotheses (from the model) to allow inclusively."
},
"model": {
"type": "string",
"description": "The tessdata text recognition model to apply (an ISO 639-3 language specification or some other basename, e.g. deu-frak or Fraktur)."
}
}
},
"ocrd-tesserocr-segment": {
"executable": "ocrd-tesserocr-segment",
"categories": ["Layout analysis"],
"description": "Segment page into regions and lines with Tesseract",
"input_file_grp": [
"OCR-D-IMG",
"OCR-D-SEG-PAGE",
"OCR-D-GT-SEG-PAGE"
],
"output_file_grp": [
"OCR-D-SEG-LINE"
],
"steps": ["layout/segmentation/region", "layout/segmentation/line"],
"parameters": {
"dpi": {
"type": "number",
"format": "float",
"description": "pixel density in dots per inch (overrides any meta-data in the images); disabled when negative",
"default": 0
},
"padding": {
"type": "number",
"format": "integer",
"description": "extend detected region rectangles by this many (true) pixels",
"default": 4
},
"block_polygons": {
"type": "boolean",
"default": false,
"description": "annotate polygon coordinates instead of bounding box rectangles"
},
"find_tables": {
"type": "boolean",
"default": true,
"description": "recognise tables as table regions (textord_tabfind_find_tables)"
},
"sparse_text": {
"type": "boolean",
"default": false,
"description": "use 'sparse text' page segmentation mode (find as much text as possible in no particular order): only text regions, single lines without vertical or horizontal space"
}
}
},
"ocrd-tesserocr-segment-region": {
"executable": "ocrd-tesserocr-segment-region",
"categories": ["Layout analysis"],
"description": "Segment page into regions with Tesseract",
"input_file_grp": [
"OCR-D-IMG",
"OCR-D-SEG-PAGE",
"OCR-D-GT-SEG-PAGE"
],
"output_file_grp": [
"OCR-D-SEG-BLOCK"
],
"steps": ["layout/segmentation/region"],
"parameters": {
"dpi": {
"type": "number",
"format": "float",
"description": "pixel density in dots per inch (overrides any meta-data in the images); disabled when negative",
"default": 0
},
"overwrite_regions": {
"type": "boolean",
"default": true,
"description": "Remove existing layout and text annotation below the Page level (otherwise skip page; no incremental annotation yet)."
},
"padding": {
"type": "number",
"format": "integer",
"description": "extend detected region rectangles by this many (true) pixels",
"default": 0
},
"crop_polygons": {
"type": "boolean",
"default": false,
"description": "annotate polygon coordinates instead of bounding box rectangles"
},
"find_tables": {
"type": "boolean",
"default": true,
"description": "recognise tables as table regions (textord_tabfind_find_tables)"
},
"sparse_text": {
"type": "boolean",
"default": false,
"description": "use 'sparse text' page segmentation mode (find as much text as possible in no particular order): only text regions, single lines without vertical or horizontal space"
}
}
},
"ocrd-tesserocr-segment-table": {
"executable": "ocrd-tesserocr-segment-table",
"categories": ["Layout analysis"],
"description": "Segment table regions into cell text regions with Tesseract",
"input_file_grp": [
"OCR-D-SEG-BLOCK",
"OCR-D-GT-SEG-BLOCK"
],
"output_file_grp": [
"OCR-D-SEG-BLOCK"
],
"steps": ["layout/segmentation/region"],
"parameters": {
"dpi": {
"type": "number",
"format": "float",
"description": "pixel density in dots per inch (overrides any meta-data in the images); disabled when negative",
"default": 0
},
"overwrite_cells": {
"type": "boolean",
"default": true,
"description": "Remove existing layout and text annotation below the TableRegion level (otherwise skip table; no incremental annotation yet)."
}
}
},
"ocrd-tesserocr-segment-line": {
"executable": "ocrd-tesserocr-segment-line",
"categories": ["Layout analysis"],
"description": "Segment regions into lines with Tesseract",
"input_file_grp": [
"OCR-D-SEG-BLOCK",
"OCR-D-GT-SEG-BLOCK"
],
"output_file_grp": [
"OCR-D-SEG-LINE"
],
"steps": ["layout/segmentation/line"],
"parameters": {
"dpi": {
"type": "number",
"format": "float",
"description": "pixel density in dots per inch (overrides any meta-data in the images); disabled when negative",
"default": 0
},
"overwrite_lines": {
"type": "boolean",
"default": true,
"description": "Remove existing layout and text annotation below the TextRegion level (otherwise skip region; no incremental annotation yet)."
}
}
},
"ocrd-tesserocr-segment-word": {
"executable": "ocrd-tesserocr-segment-word",
"categories": ["Layout analysis"],
"description": "Segment lines into words with Tesseract",
"input_file_grp": [
"OCR-D-SEG-LINE",
"OCR-D-GT-SEG-LINE"
],
"output_file_grp": [
"OCR-D-SEG-WORD"
],
"steps": ["layout/segmentation/word"],
"parameters": {
"dpi": {
"type": "number",
"format": "float",
"description": "pixel density in dots per inch (overrides any meta-data in the images); disabled when negative",
"default": 0
},
"overwrite_words": {
"type": "boolean",
"default": true,
"description": "Remove existing layout and text annotation below the TextLine level (otherwise skip line; no incremental annotation yet)."
}
}
},
"ocrd-tesserocr-crop": {
"executable": "ocrd-tesserocr-crop",
"categories": ["Image preprocessing"],
"description": "Poor man's cropping via region segmentation",
"input_file_grp": [
"OCR-D-IMG"
],
"output_file_grp": [
"OCR-D-SEG-PAGE"
],
"steps": ["preprocessing/optimization/cropping"],
"parameters" : {
"dpi": {
"type": "number",
"format": "float",
"description": "pixel density in dots per inch (overrides any meta-data in the images); disabled when negative",
"default": 0
},
"padding": {
"type": "number",
"format": "integer",
"description": "extend detected border by this many (true) pixels on every side",
"default": 4
}
}
},
"ocrd-tesserocr-binarize": {
"executable": "ocrd-tesserocr-binarize",
"categories": ["Image preprocessing"],
"description": "Binarize regions or lines with Tesseract's global Otsu",
"input_file_grp": [
"OCR-D-IMG",
"OCR-D-SEG-BLOCK",
"OCR-D-SEG-LINE"
],
"output_file_grp": [
"OCR-D-BIN-BLOCK",
"OCR-D-BIN-LINE"
],
"steps": ["preprocessing/optimization/binarization"],
"parameters": {
"operation_level": {
"type": "string",
"enum": ["region", "line"],
"default": "region",
"description": "PAGE XML hierarchy level to operate on"
}
}
}
}
}