python - Preserving indentation with Tesseract OCR 4.x

Question

I'm struggling with Tesseract OCR. I have a blood examination image, it has a table with indentation. Although tesseract recognizes the characters very well, its structure isn't preserved in the final output. For example, look the lines below "Emocromo con formula" (Eng. Translation: blood count with formula) that are indented. I want to preserve that indentation.

I read the other related discussions and I found the option preserve_interword_spaces=1. The result became slightly better but as you can see, it isn't perfect.

Any suggestions?

Update:

I tried Tesseract v5.0 and the result is the same.

Code:

Tesseract version is 4.0.0.20190314

from PIL import Image
import pytesseract

# Preserve interword spaces is set to 1, oem = 1 is LSTM, 
# PSM = 1 is Automatic page segmentation with OSD - Orientation and script detection

custom_config = r'-c preserve_interword_spaces=1 --oem 1 --psm 1 -l eng+ita'

# default_config = r'-c -l eng+ita'

extracted_text = pytesseract.image_to_string(Image.open('referto-1.jpg'), config=custom_config)

print(extracted_text)

# saving to a txt file

with open("referto.txt", "w") as text_file:
    text_file.write(extracted_text)

Result with comparison:

GITHUB:

I have created a GitHub repository if you want to try it yourself.

Thanks for your help and your time

Answer 1

image_to_data() function provides much more information. For each word it will return it's bounding rectangle. You can use that.

Tesseract segments the image automatically to blocks. Then you can sort block by their vertical position and for each block you can find mean character width (that depends on the block's recognized font). Then for each word in the block check if it is close to the previous one, if not add spaces accordingly. I'm using pandas to ease on calculations, but it's usage is not necessary. Don't forget that the result should be displayed using monospaced font.

import pytesseract
from pytesseract import Output
from PIL import Image
import pandas as pd

custom_config = r'-c preserve_interword_spaces=1 --oem 1 --psm 1 -l eng+ita'
d = pytesseract.image_to_data(Image.open(r'referto-2.jpg'), config=custom_config, output_type=Output.DICT)
df = pd.DataFrame(d)

# clean up blanks
df1 = df[(df.conf!='-1')&(df.text!=' ')&(df.text!='')]
# sort blocks vertically
sorted_blocks = df1.groupby('block_num').first().sort_values('top').index.tolist()
for block in sorted_blocks:
    curr = df1[df1['block_num']==block]
    sel = curr[curr.text.str.len()>3]
    char_w = (sel.width/sel.text.str.len()).mean()
    prev_par, prev_line, prev_left = 0, 0, 0
    text = ''
    for ix, ln in curr.iterrows():
        # add new line when necessary
        if prev_par != ln['par_num']:
            text += '
'
            prev_par = ln['par_num']
            prev_line = ln['line_num']
            prev_left = 0
        elif prev_line != ln['line_num']:
            text += '
'
            prev_line = ln['line_num']
            prev_left = 0

        added = 0  # num of spaces that should be added
        if ln['left']/char_w > prev_left + 1:
            added = int((ln['left'])/char_w) - prev_left
            text += ' ' * added 
        text += ln['text'] + ' '
        prev_left += len(ln['text']) + added + 1
    text += '
'
    print(text)

This code will produce following output:

    ssseeess+ SERVIZIO SANITARIO REGIONALE                          Pagina 2 di3 
   seoeeeees EMILIA-RROMAGNA 
     ?2888   800 
     ?9868  6 006   :       pe   ‘  ‘        " 
     ?ee @@e@ecee Azienda Unita Sanitaria Locale di Modena 
     Seat se  ces Amends Ospedaliero-Universitaria Policlinico di Modena 
         Dipartimento  interaziendale ad attivita integrata di Medicina di Laboratorio e Anatomia Patologica 
                                                  Direttore dr. T.Trenti 
                                           Ospedale Civile S.Agostino-Estense 
                                             S.C. Medicina  di Laboratorio 
                                           S.S. Patologia  Clinica - Corelab 
                            Sistema di Gestione per la Qualita certificato UNI EN ISO 9001:2015 
                                              Responsabile dr.ssa M.Varani 
        Richiesta (CDA):   49/073914                                    Data di accettazione: 18/12/2018 
                                                                        Data di check-in:    18/12/2018 10:27:06 
                                                                        Referto del          18/12/2018 16:39:53 
                                                                        Provenienza:         D4-cp sassuolo 

                                                           Sig. 
                                                           Data di Nascita: 
                                                           Domicilio: 
          ANALISI                                              RISULTATO  __UNITA'DI MISURA VALORI DI RIFERIMENTO 
       Glucosio                                                     95     mg/dl            (70  - 110 ) 
       Creatinina                                                 1.03     mg/dl            ( 0.50 - 1.40 ) 
       eGFR  Filtrato glomerulare stimato                         >60      ml/min           Cut-off per rischio di  I.R. 
             7                                                                              <60. Il calcolo é€ riferito 
       Equazione  CKD-EPI                                                                   ad una superfice corporea 
                                                                                            Standard  (1,73 mq)x In Caso 
                                                                                            di etnia afroamericana 
                                                                                            moltiplicare per  il fattore 
                                                                                            1,159. 
       Colesterolo                                                212   *  mg/dl            < 200 v.desiderabile 
       Trigliceridi                                                106     mg/dl            < 180 v.desiderabile 
       Bilirubina totale                                          0.60     mg/dl            ( 0.16 - 1.10 ) 
       Bilirubina diretta                                         0.10     mg/dl            ( 0.01 - 0.3 ) 
       GOT  - AST                                                   17     U/L              (1-37) 
       GPT  - ALT                                                   ay     U/L              (1-   40 ) 
       Gamma-GT                                                     15     U/L              (1-55) 
       Sodio                                                       142     mEq/L            ( 136 - 146 ) 
       Potassio                                                    4.3     mEq/L            (3.5  - 5.3) 
       Vitamina B12                                               342      pg/ml            ( 200 - 960 ) 
       TSH                                                        5.47  *  ulU/ml           (0.35  - 4.94 ) 
       FT4                                                         9.7     pg/ml            (7  = 15) 
       Urine chimico fisico morfologico 
          u-Colore                                     giallo paglierino 
          u-Peso specifico                                       1.012                      ( 1.010 - 1.027  ) 
          u-pH                                                     5.5                      (5.5  - 6.5) 
          u-Glucosio                                           assente     mg/dl            assente 
          u-Proteine                                           assente     mg/dl            (0  -10 ) 
          u-Emoglobina                                         assente     mg/dl            assente 
          u-Corpi chetonici                                    assente     mg/dl            assente 
          u-Bilirubina                                         assente     mg/dl            assente 
          u-Urobilinogeno                                         0.20     mg/dl            (0-   1.0 ) 
          sedimento                                    non significativo 
                                                                                          Il Laureato: 
                                                                                                     Dott. CRISTINA ROTA 
       Per ogni informazione o chiarimento sugli aspetti medici, puo rivolgersi al suo medico curante 
       Referto firmato elettronicamente secondo le norme vigenti: Legge 15 marzo 1997, n. 59; D.P.R. 10 novembre 1997, n.513; 
       D.P.C.M. 8 febbraio 1999; D.P.R 28 dicembre 2000, n.445; D.L. 23 gennaio 2002, n.10. 
       Certificato rilasciato da: Infocamere S.C.p.A. (http://www.card.infocamere. it) 
       i! Laureato: Dr. CRISTINA ROTA 
       1! documento informatico originale 6 conservato presso Parer - Polo Archivistico della Regione Emilia-Romagna