I suspect the way it works is that if you say it can only recognise the
letter "S" then it will interpret "5" and "$" etc as "S".
What you need to do is allow it to recognise all of the chars that you
actually expect to see in the document, and then write a script to remove
them from the result.
So my tessedit_char_whitelist is "1234567890
abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ\"-–—.,;:'()*&?!/"
And then I have a script that removes any chars that are not
in "1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ.\"-'&"
On Sat, 3 May 2025 at 18:07, Burt Bacharat <splif...@gmail.com> wrote:
> I'm trying to figure out how to disable all the language model behaviour
> and just do character recognition and word-splitting on whitespace. I've
> tried different `--oem` modes including mode 0 with a legacy language file
> but tesseract still keeps trying to correct words/characters based on
> surrounding characters.
>
> Say I have a "word" consisting of a letter and a number, like "S9" or
> "S99". Depending on the combination of settings I use I will usually get
> one of these incorrect behaviours:
> - The S is substituted for a "$" (dollar sign) because it thinks it's
> currency
> - The S is substituted for an "8" because it thinks it's a number
>
> In most other situations it will see the same S correctly (ie, as part of
> an actual word). It's only when I mix letters and numbers that this
> behaviour is triggered which suggests this is not a character recognition
> issue in the traditional sense of just detecting the outline.
>
> I should add the input I'm scanning is from a digital file and it's a
> high-res, low-noise document with high contrast and a clean serif font.
> Noise/artifacts are not really an issue and DPI can be be as high as
> required. I'm currently scanning at 300 DPI (approx 8000x12000px) but I can
> increase or decrease it if will help (it doesn't seem to).
>
> I've tried disabling every relevant option I can find and it still keeps
> happening. Here is the full list of settings I'm passing:
>
> CUSTOM_TESSERACT_CONFIG = (
> '--oem 0 --psm 6 '
> f'-c tessedit_char_whitelist="{VALID_CHARS}" '
> '-c tessedit_enable_dict_correction=0 '
> '-c load_system_dawg=0 '
> '-c load_freq_dawg=0 '
> '-c load_punc_dawg=0 '
> '-c load_number_dawg=0 '
> '-c load_unambig_dawg=0 '
> '-c load_bigram_dawg=0 '
> '-c load_fixed_length_dawgs=0 '
> '-c wordrec_enable_assoc=0 '
> '-c language_model_penalty_non_freq_dict_word=0 '
> '-c language_model_penalty_non_dict_word=0 '
> '-c tessedit_prefer_joined_punct=1 '
> '-c textord_enable_word_ngrams=0 '
> '-c tessedit_good_quality_unrej=1 '
> '-c tessedit_enable_bigram_correction=0 '
> '-c tessedit_enable_doc_dict=0 '
> '-c textord_enable_out_of_punct=0 '
> '-c textord_enable_xheight_stats=0 '
> '-c enable_noise_removal=0 '
> '-c classify_enable_adaptive_matcher=0 '
> '-c classify_enable_learning=0 '
> '-c tessedit_preserve_blk_rej_perfect_wds=1 '
> '-c preserve_interword_spaces=1 '
> '-c segment_penalty_dict_case=0 '
> '-c segment_penalty_garbage=0 '
> '-c textord_split_num_pattern=0'
> )
>
> Basically what I'm after is for tesseract to do ONLY these things:
>
> a.) Detect a character based only on its outline, not the surrounding
> context - and use the best match.
> b.) Group nearby characters into groups based only on whitespace (no
> splitting on commas, punctuation, etc) however I do want to capture the
> punctuation (eg: $9,999.00)
> c.) Give me the bounding box of each group (because I need the position
> for further processing)
>
> How can I do this? Is it even possible?
>
> ----
> tesseract -v
> tesseract 5.5.0
> leptonica-1.85.0
> libgif 5.2.2 : libjpeg 8d (libjpeg-turbo 3.0.4) : libpng 1.6.47 :
> libtiff 4.7.0 : zlib 1.2.12 : libwebp 1.5.0 : libopenjp2 2.5.3
> Found NEON
> Found libarchive 3.7.7 zlib/1.2.12 liblzma/5.6.3 bz2lib/1.0.8
> liblz4/1.10.0 libzstd/1.5.6
> Found libcurl/8.7.1 SecureTransport (LibreSSL/3.3.6) zlib/1.2.12
> nghttp2/1.61.0
>
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