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Does Tesseract's hOCR output really contain bounding boxes and confidence levels for each character?
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Solved ocrtesseracthocr
M

2

7

In the Tesseract FAQ they say you can:

How can I get the coordinates and confidence of each character?

There are two options. If you would rather not get into programming, you can use Tesseract's hocr output format (read the Tesseract manual page for details).

But when I created a sample hOCR output (it's an .html file), the bounding boxes and confidence levels were only available at the word level.

Am I missing something here?

I've added the sample input/output as illustration (the input is resized).

This is the input image:

enter image description here

This is Tesseract's hOCR output:

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title></title>
<meta http-equiv="Content-Type" content="text/html;charset=utf-8" />
<meta name='ocr-system' content='tesseract'/>
</head>
<body>
<div class='ocr_page' id='page_1' title='image "in2.tif"; bbox 0 0 1882 354'>
<div class='ocr_carea' id='block_1_1' title="bbox 78 59 457 100">
<p class='ocr_par'>
<span class='ocr_line' id='line_1_1' title="bbox 78 61 456 97"><span class='ocr_word' id='word_1_1' title="bbox 78 62 175 97"><span class='ocrx_word' id='xword_1_1' title="x_wconf -2">Dear</span></span> <span class='ocr_word' id='word_1_2' title="bbox 205 62 271 96"><span class='ocrx_word' id='xword_1_2' title="x_wconf -14">Mr:</span></span> <span class='ocr_word' id='word_1_3' title="bbox 303 61 456 97"><span class='ocrx_word' id='xword_1_3' title="x_wconf -2">Grover:</span></span></span>
</p>
</div>
<div class='ocr_carea' id='block_1_2' title="bbox 75 154 1842 317">
<p class='ocr_par'>
<span class='ocr_line' id='line_1_2' title="bbox 78 161 1787 210"><span class='ocr_word' id='word_1_4' title="bbox 78 161 111 196"><span class='ocrx_word' id='xword_1_4' title="x_wconf -2">If</span></span> <span class='ocr_word' id='word_1_5' title="bbox 137 161 270 205"><span class='ocrx_word' id='xword_1_5' title="x_wconf -2">you&#39;ve</span></span> <span class='ocr_word' id='word_1_6' title="bbox 298 162 393 197"><span class='ocrx_word' id='xword_1_6' title="x_wconf -1">been</span></span> <span class='ocr_word' id='word_1_7' title="bbox 422 161 571 206"><span class='ocrx_word' id='xword_1_7' title="x_wconf -3">looking</span></span> <span class='ocr_word' id='word_1_8' title="bbox 598 162 657 197"><span class='ocrx_word' id='xword_1_8' title="x_wconf -2">for</span></span> <span class='ocr_word' id='word_1_9' title="bbox 685 174 707 198"><span class='ocrx_word' id='xword_1_9' title="x_wconf -1">a</span></span> <span class='ocr_word' id='word_1_10' title="bbox 734 162 929 207"><span class='ocrx_word' id='xword_1_10' title="x_wconf -4">reporting</span></span> <span class='ocr_word' id='word_1_11' title="bbox 956 163 1031 198"><span class='ocrx_word' id='xword_1_11' title="x_wconf -1">tool</span></span> <span class='ocr_word' id='word_1_12' title="bbox 1059 162 1140 199"><span class='ocrx_word' id='xword_1_12' title="x_wconf -3">that</span></span> <span class='ocr_word' id='word_1_13' title="bbox 1168 164 1294 199"><span class='ocrx_word' id='xword_1_13' title="x_wconf -4">allows</span></span> <span class='ocr_word' id='word_1_14' title="bbox 1321 175 1428 200"><span class='ocrx_word' id='xword_1_14' title="x_wconf -1">users</span></span> <span class='ocr_word' id='word_1_15' title="bbox 1456 169 1494 200"><span class='ocrx_word' id='xword_1_15' title="x_wconf -3">to</span></span> <span class='ocr_word' id='word_1_16' title="bbox 1523 169 1649 200"><span class='ocrx_word' id='xword_1_16' title="x_wconf -2">create</span></span> <span class='ocr_word' id='word_1_17' title="bbox 1677 170 1787 210"><span class='ocrx_word' id='xword_1_17' title="x_wconf -3">great</span></span></span>
<span class='ocr_line' id='line_1_3' title="bbox 77 210 1841 260"><span class='ocr_word' id='word_1_18' title="bbox 77 210 226 256"><span class='ocrx_word' id='xword_1_18' title="x_wconf -3">looking</span></span> <span class='ocr_word' id='word_1_19' title="bbox 253 216 399 256"><span class='ocrx_word' id='xword_1_19' title="x_wconf -4">reports</span></span> <span class='ocr_word' id='word_1_20' title="bbox 427 211 581 256"><span class='ocrx_word' id='xword_1_20' title="x_wconf -3">quickly,</span></span> <span class='ocr_word' id='word_1_21' title="bbox 613 224 654 248"><span class='ocrx_word' id='xword_1_21' title="x_wconf -2">as</span></span> <span class='ocr_word' id='word_1_22' title="bbox 682 213 763 248"><span class='ocrx_word' id='xword_1_22' title="x_wconf -1">well</span></span> <span class='ocr_word' id='word_1_23' title="bbox 792 224 832 248"><span class='ocrx_word' id='xword_1_23' title="x_wconf -1">as</span></span> <span class='ocr_word' id='word_1_24' title="bbox 859 212 1056 258"><span class='ocrx_word' id='xword_1_24' title="x_wconf -4">providing</span></span> <span class='ocr_word' id='word_1_25' title="bbox 1083 212 1144 249"><span class='ocrx_word' id='xword_1_25' title="x_wconf -2">the</span></span> <span class='ocr_word' id='word_1_26' title="bbox 1173 214 1315 249"><span class='ocrx_word' id='xword_1_26' title="x_wconf -2">control</span></span> <span class='ocr_word' id='word_1_27' title="bbox 1344 215 1417 249"><span class='ocrx_word' id='xword_1_27' title="x_wconf -2">and</span></span> <span class='ocr_word' id='word_1_28' title="bbox 1445 214 1639 250"><span class='ocrx_word' id='xword_1_28' title="x_wconf -2">industrial</span></span> <span class='ocr_word' id='word_1_29' title="bbox 1667 215 1841 260"><span class='ocrx_word' id='xword_1_29' title="x_wconf -3">strength</span></span></span>
<span class='ocr_line' id='line_1_4' title="bbox 76 260 1370 306"><span class='ocr_word' id='word_1_30' title="bbox 76 261 243 296"><span class='ocrx_word' id='xword_1_30' title="x_wconf -2">features</span></span> <span class='ocr_word' id='word_1_31' title="bbox 272 260 353 297"><span class='ocrx_word' id='xword_1_31' title="x_wconf -2">that</span></span> <span class='ocr_word' id='word_1_32' title="bbox 381 273 427 297"><span class='ocrx_word' id='xword_1_32' title="x_wconf -1">an</span></span> <span class='ocr_word' id='word_1_33' title="bbox 458 261 499 297"><span class='ocrx_word' id='xword_1_33' title="x_wconf -2">IS</span></span> <span class='ocr_word' id='word_1_34' title="bbox 527 262 776 306"><span class='ocrx_word' id='xword_1_34' title="x_wconf -2">professional</span></span> <span class='ocr_word' id='word_1_35' title="bbox 804 263 1110 299"><span class='ocrx_word' id='xword_1_35' title="x_wconf -2">demands...look</span></span> <span class='ocr_word' id='word_1_36' title="bbox 1139 275 1184 299"><span class='ocrx_word' id='xword_1_36' title="x_wconf -1">no</span></span> <span class='ocr_word' id='word_1_37' title="bbox 1212 263 1370 299"><span class='ocrx_word' id='xword_1_37' title="x_wconf -3">further!</span></span></span>
</p>
</div>
</div>
</body>
</html>
Mccreery answered 5/4, 2013 at 8:24 Comment(1)
Answer at https://mcmap.net/q/1481491/-how-to-get-character-wise-confidence-in-tesseract-using-command-line – Hortensiahorter
G
6

You've seen it: it isn't there.

So you can either modify Tesseract source code to output hOCR format that supports x_confs property that you want or use its ResultIterator API class to get confidence at the character (symbol) level (be sure to SetVariable("save_blob_choices", "T") after Init method).

Gastroenteritis answered 9/4, 2013 at 5:3 Comment(3)
Are sure it's save_blob_choices? I can't find it in the source code, the closest thing I find is save_best_choices. I'm using Tesseract 3.01. – Mccreery
It could have been changed for 3.02, which is what I'm using. I tried save_best_choices but it did not produce character-level confidence. – Gastroenteritis
For the record, save_best_choices worked for me on Tesseract 3.01 – Mccreery
H
4

This now seems to be available in Tesseract 4.x.

See my answer at:

https://mcmap.net/q/1481491/-how-to-get-character-wise-confidence-in-tesseract-using-command-line

Set hocr_char_boxes to 1 in your config file. Or, at the command line, your updated command would be:

tesseract [Image name] outputbase --oem 1 -l eng --psm 8 -c hocr_char_boxes=1 hocr Note the hocr output option and look in that file for ..._wconf, e.g.

Let me know if this works for you, otherwise I'll just delete the answer.

Source: https://github.com/tesseract-ocr/tesseract/issues/1465#issuecomment-513139976

Hortensiahorter answered 4/9, 2019 at 7:1 Comment(0)

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