mmocr/docs/en/tutorials/blank_recog.md

Enable Blank Space Recognition

It is noteworthy that the LineStrParser should NOT be used to parse the annotation files containing multiple blank spaces (in file name or recognition transcriptions). The users have to convert the plain txt annotations to json lines to enable space recognition. For example:

% A plain txt annotation file that contains blank spaces
test/img 1.jpg Hello World!
test/img 2.jpg Hello Open MMLab!
test/img 3.jpg Hello MMOCR!

The LineStrParser will split the above annotation line to pieces (e.g. ['test/img', '1.jpg', 'Hello', 'World!']) that cannot be matched to the keys (e.g. ['filename', 'text']). Therefore, we need to convert it to a json line format by json.dumps (check here to see how to dump jsonl), and then the annotation file will look like as follows:

% A json line annotation file that contains blank spaces
{"filename": "test/img 1.jpg", "text": "Hello World!"}
{"filename": "test/img 2.jpg", "text": "Hello Open MMLab!"}
{"filename": "test/img 3.jpg", "text": "Hello MMOCR!"}

After converting the annotation format, you just need to set the parser arguments as:

parser=dict(
    type='LineJsonParser',
    keys=['filename', 'text']))

Besides, you need to specify a dict that contains blank space to enable blank recognition. Particularly, MMOCR provides two built-in dicts DICT37 and DICT91 that contain blank space. For example, change the default dict_type in configs/_base_/recog_models/crnn.py to DICT37.

label_convertor = dict(
    type='CTCConvertor', dict_type='DICT37', with_unknown=False, lower=True) # ['DICT36', 'DICT37', 'DICT90', 'DICT91']