Choosing the right model#

The full Optical Character Recognition task can be seen as two consecutive tasks: text detection and text recognition. Either performed at once or separately, to each task corresponds a type of deep learning architecture.

For a given task, docTR provides a Predictor, which is composed of 2 components:

PreProcessor: a module in charge of making inputs directly usable by the deep learning model.
Model: a deep learning model, implemented with all supported deep learning backends (TensorFlow & PyTorch) along with its specific post-processor to make outputs structured and reusable.

Text Detection#

The task consists of localizing textual elements in a given image. While those text elements can represent many things, in docTR, we will consider uninterrupted character sequences (words). Additionally, the localization can take several forms: from straight bounding boxes (delimited by the 2D coordinates of the top-left and bottom-right corner), to polygons, or binary segmentation (flagging which pixels belong to this element, and which don’t). Our latest detection models works with rotated and skewed documents!

Available architectures#

The following architectures are currently supported:

We also provide 2 models working with any kind of rotated documents:

linknet_resnet18_rotation (TensorFlow)
db_resnet50_rotation (PyTorch)

For a comprehensive comparison, we have compiled a detailed benchmark on publicly available datasets:

				FUNSD		CORD
Backend	Architecture	Input shape	# params	Recall	Precision	Recall	Precision	sec/it (B: 1)
TensorFlow	db_resnet50	(1024, 1024, 3)	25.2 M	81.22	86.66	92.46	89.62	1.2
Tensorflow	db_mobilenet_v3_large	(1024, 1024, 3)	4.2 M	78.27	82.77	80.99	66.57	0.5
TensorFlow	linknet_resnet18	(1024, 1024, 3)	11.5 M	78.23	83.77	82.88	82.42	0.7
Tensorflow	linknet_resnet18_rotation	(1024, 1024, 3)	11.5 M	81.12	82.13	83.55	80.14	0.6
TensorFlow	linknet_resnet34	(1024, 1024, 3)	21.6 M	82.14	87.64	85.55	86.02	0.8
Tensorflow	linknet_resnet50	(1024, 1024, 3)	28.8 M	79.00	84.79	85.89	65.75	1.1
PyTorch	db_resnet34	(1024, 1024, 3)	22.4 M
PyTorch	db_resnet50	(1024, 1024, 3)	25.4 M	79.17	86.31	92.96	91.23	1.1
PyTorch	db_resnet50_rotation	(1024, 1024, 3)	25.4 M	83.30	91.07	91.63	90.53	1.6
PyTorch	db_mobilenet_v3_large	(1024, 1024, 3)	4.2 M	80.06	84.12	80.51	66.51	0.5
PyTorch	linknet_resnet18	(1024, 1024, 3)	11.5 M
PyTorch	linknet_resnet34	(1024, 1024, 3)	21.6 M
PyTorch	linknet_resnet50	(1024, 1024, 3)	28.8 M

All text detection models above have been evaluated using both the training and evaluation sets of FUNSD and CORD (cf. doctr.datasets). Explanations about the metrics being used are available in Task evaluation.

Disclaimer: both FUNSD subsets combined have 199 pages which might not be representative enough of the model capabilities

Seconds per iteration (with a batch size of 1) is computed after a warmup phase of 100 tensors, by measuring the average number of processed tensors per second over 1000 samples. Those results were obtained on a 11th Gen Intel(R) Core(TM) i7-11800H @ 2.30GHz.

Detection predictors#

detection_predictor wraps your detection model to make it easily useable with your favorite deep learning framework seamlessly.

import numpy as np
from doctr.models import detection_predictor
predictor = detection_predictor('db_resnet50')
dummy_img = (255 * np.random.rand(800, 600, 3)).astype(np.uint8)
out = model([dummy_img])

You can pass specific boolean arguments to the predictor:

assume_straight_pages: if you work with straight documents only, it will fit straight bounding boxes to the text areas.
preserve_aspect_ratio: if you want to preserve the aspect ratio of your documents while resizing before sending them to the model.
symmetric_pad: if you choose to preserve the aspect ratio, it will pad the image symmetrically and not from the bottom-right.

For instance, this snippet will instantiates a detection predictor able to detect text on rotated documents while preserving the aspect ratio:

from doctr.models import detection_predictor
predictor = detection_predictor('db_resnet50_rotation', pretrained=True, assume_straight_pages=False, preserve_aspect_ratio=True)

NB: for the moment, db_resnet50_rotation is pretrained in Pytorch only and linknet_resnet18_rotation in Tensorflow only.

Text Recognition#

The task consists of transcribing the character sequence in a given image.

Available architectures#

The following architectures are currently supported:

For a comprehensive comparison, we have compiled a detailed benchmark on publicly available datasets:

				FUNSD		CORD
Backend	Architecture	Input shape	# params	Exact	Partial	Exact	Partial	sec/it (B: 64)
TensorFlow	crnn_vgg16_bn	(32, 128, 3)	15.8 M	88.12	88.85	94.68	95.10	0.9
Tensorflow	crnn_mobilenet_v3_small	(32, 128, 3)	2.1 M	86.88	87.61	92.28	92.73	0.25
TensorFlow	crnn_mobilenet_v3_large	(32, 128, 3)	4.5 M	87.44	88.12	94.14	94.55	0.34
Tensorflow	master	(32, 128, 3)	58.8 M	87.44	88.21	93.83	94.25	22.3
TensorFlow	sar_resnet31	(32, 128, 3)	57.2 M	87.67	88.48	94.21	94.66	7.1
Tensorflow	vitstr_small	(32, 128, 3)	21.4 M	83.01	83.84	86.57	87.00	2.0
TensorFlow	vitstr_base	(32, 128, 3)	85.2 M	85.98	86.70	90.47	90.95	5.8
TensorFlow	parseq	(32, 128, 3)	23.8 M	81.62	82.29	79.13	79.52	3.6
PyTorch	crnn_vgg16_bn	(32, 128, 3)	15.8 M	86.54	87.41	94.29	94.69	0.6
PyTorch	crnn_mobilenet_v3_small	(32, 128, 3)	2.1 M	87.25	87.99	93.91	94.34	0.05
PyTorch	crnn_mobilenet_v3_large	(32, 128, 3)	4.5 M	87.38	88.09	94.46	94.92	0.08
PyTorch	master	(32, 128, 3)	58.7 M					17.6
PyTorch	sar_resnet31	(32, 128, 3)	55.4 M					4.9
PyTorch	vitstr_small	(32, 128, 3)	21.4 M					1.5
PyTorch	vitstr_base	(32, 128, 3)	85.2 M					4.1
PyTorch	parseq	(32, 128, 3)	23.8 M					2.2

All text recognition models above have been evaluated using both the training and evaluation sets of FUNSD and CORD (cf. doctr.datasets). Explanations about the metric being used (exact match) are available in Task evaluation.

While most of our recognition models were trained on our french vocab (cf. Supported Vocabs), you can easily access the vocab of any model as follows:

from doctr.models import recognition_predictor
predictor = recognition_predictor('crnn_vgg16_bn')
print(predictor.model.cfg['vocab'])

Disclaimer: both FUNSD subsets combine have 30595 word-level crops which might not be representative enough of the model capabilities

Seconds per iteration (with a batch size of 64) is computed after a warmup phase of 100 tensors, by measuring the average number of processed tensors per second over 1000 samples. Those results were obtained on a 11th Gen Intel(R) Core(TM) i7-11800H @ 2.30GHz.

Recognition predictors#

recognition_predictor wraps your recognition model to make it easily useable with your favorite deep learning framework seamlessly.

import numpy as np
from doctr.models import recognition_predictor
predictor = recognition_predictor('crnn_vgg16_bn')
dummy_img = (255 * np.random.rand(50, 150, 3)).astype(np.uint8)
out = model([dummy_img])

End-to-End OCR#

The task consists of both localizing and transcribing textual elements in a given image.

Available architectures#

You can use any combination of detection and recognition models supported by docTR.

For a comprehensive comparison, we have compiled a detailed benchmark on publicly available datasets:

		FUNSD		CORD
Backend	Architecture	Recall \| Precision		Recall	Precision
TensorFlow	db_resnet50 + crnn_vgg16_bn	70.82	75.56	83.97	81.40
TensorFlow	db_resnet50 + crnn_mobilenet_v3_small	69.63	74.29	81.08	78.59
TensorFlow	db_resnet50 + crnn_mobilenet_v3_large	70.01	74.70	83.28	80.73
TensorFlow	db_resnet50 + sar_resnet31	68.75	73.76	78.56	76.24
TensorFlow	db_resnet50 + master	68.75	73.76	78.56	76.24
TensorFlow	db_resnet50 + vitstr_small	64.58	68.91	74.66	72.37
TensorFlow	db_resnet50 + vitstr_base	66.89	71.37	79.11	76.68
TensorFlow	db_resnet50 + parseq	65.77	70.18	71.57	69.37
PyTorch	db_resnet50 + crnn_vgg16_bn	67.82	73.35	84.84	83.27
PyTorch	db_resnet50 + crnn_mobilenet_v3_small	67.89	74.01	84.43	82.85
PyTorch	db_resnet50 + crnn_mobilenet_v3_large	68.45	74.63	84.86	83.27
PyTorch	db_resnet50 + sar_resnet31
PyTorch	db_resnet50 + master
PyTorch	db_resnet50 + vitstr_small
PyTorch	db_resnet50 + vitstr_base
PyTorch	db_resnet50 + parseq
None	Gvision text detection	59.50	62.50	75.30	59.03
None	Gvision doc. text detection	64.00	53.30	68.90	61.10
None	AWS textract	78.10	83.00	87.50	66.00
None	Azure Form Recognizer (v3.2)	79.42	85.89	89.62	88.93

All OCR models above have been evaluated using both the training and evaluation sets of FUNSD and CORD (cf. doctr.datasets). Explanations about the metrics being used are available in Task evaluation.

Disclaimer: both FUNSD subsets combine have 199 pages which might not be representative enough of the model capabilities

Two-stage approaches#

Those architectures involve one stage of text detection, and one stage of text recognition. The text detection will be used to produces cropped images that will be passed into the text recognition block. Everything is wrapped up with ocr_predictor.

import numpy as np
from doctr.models import ocr_predictor
model = ocr_predictor('db_resnet50', 'crnn_vgg16_bn', pretrained=True)
input_page = (255 * np.random.rand(800, 600, 3)).astype(np.uint8)
out = model([input_page])

You can pass specific boolean arguments to the predictor:

assume_straight_pages
preserve_aspect_ratio
symmetric_pad

Those 3 are going straight to the detection predictor, as mentioned above (in the detection part).

export_as_straight_boxes: If you work with rotated and skewed documents but you still want to export straight bounding boxes and not polygons, set it to True.

For instance, this snippet instantiates an end-to-end ocr_predictor working with rotated documents, which preserves the aspect ratio of the documents, and returns polygons:

from doctr.model import ocr_predictor
model = ocr_predictor('linknet_resnet18_rotation', pretrained=True, assume_straight_pages=False, preserve_aspect_ratio=True)

What should I do with the output?#

The ocr_predictor returns a Document object with a nested structure (with Page, Block, Line, Word, Artefact). To get a better understanding of our document model, check our Document structure section

Here is a typical Document layout:

Document(
  (pages): [Page(
    dimensions=(340, 600)
    (blocks): [Block(
      (lines): [Line(
        (words): [
          Word(value='No.', confidence=0.91),
          Word(value='RECEIPT', confidence=0.99),
          Word(value='DATE', confidence=0.96),
        ]
      )]
      (artefacts): []
    )]
  )]
)

You can also export them as a nested dict, more appropriate for JSON format:

json_output = result.export()

For reference, here is the export for the same Document as above:

{
  'pages': [
      {
          'page_idx': 0,
          'dimensions': (340, 600),
          'orientation': {'value': None, 'confidence': None},
          'language': {'value': None, 'confidence': None},
          'blocks': [
              {
                  'geometry': ((0.1357421875, 0.0361328125), (0.8564453125, 0.8603515625)),
                  'lines': [
                      {
                          'geometry': ((0.1357421875, 0.0361328125), (0.8564453125, 0.8603515625)),
                          'words': [
                              {
                                  'value': 'No.',
                                  'confidence': 0.914085328578949,
                                  'geometry': ((0.5478515625, 0.06640625), (0.5810546875, 0.0966796875))
                              },
                              {
                                  'value': 'RECEIPT',
                                  'confidence': 0.9949972033500671,
                                  'geometry': ((0.1357421875, 0.0361328125), (0.51171875, 0.1630859375))
                              },
                              {
                                  'value': 'DATE',
                                  'confidence': 0.9578408598899841,
                                  'geometry': ((0.1396484375, 0.3232421875), (0.185546875, 0.3515625))
                              }
                          ]
                      }
                  ],
                  'artefacts': []
              }
          ]
      }
  ]
}

To export the outpout as XML (hocr-format) you can use the export_as_xml method:

xml_output = result.export_as_xml()
for output in xml_output:
    xml_bytes_string = output[0]
    xml_element = output[1]

For reference, here is a sample XML byte string output:

<?xml version="1.0" encoding="UTF-8"?>
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
  <head>
    <title>docTR - hOCR</title>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <meta name="ocr-system" content="doctr 0.5.0" />
    <meta name="ocr-capabilities" content="ocr_page ocr_carea ocr_par ocr_line ocrx_word" />
  </head>
  <body>
    <div class="ocr_page" id="page_1" title="image; bbox 0 0 3456 3456; ppageno 0" />
    <div class="ocr_carea" id="block_1_1" title="bbox 857 529 2504 2710">
      <p class="ocr_par" id="par_1_1" title="bbox 857 529 2504 2710">
        <span class="ocr_line" id="line_1_1" title="bbox 857 529 2504 2710; baseline 0 0; x_size 0; x_descenders 0; x_ascenders 0">
          <span class="ocrx_word" id="word_1_1" title="bbox 1552 540 1778 580; x_wconf 99">Hello</span>
          <span class="ocrx_word" id="word_1_2" title="bbox 1782 529 1900 583; x_wconf 99">XML</span>
          <span class="ocrx_word" id="word_1_3" title="bbox 1420 597 1684 641; x_wconf 81">World</span>
        </span>
      </p>
    </div>
  </body>
</html>