--- /dev/null
+Handing OCR failures
+--------------------
+
+Sometimes the OCR will not be able to recognise some text. By
+default, when this happens, the program will stop with a fatal error
+and refer you to this document.
+
+It is possible to fix this by editing the character set dictionary used
+by the OCR algorithm. But, it is important to get these inputs right
+or your client may misrecognise text in future. You *must* read the
+documentation here first.
+
+
+Recognition algorithm
+---------------------
+
+We recognise the text in the commodity screen by doing exact matching
+of `glyph' images, against the image in each cell in the commodity
+table. We match from left to right.
+
+We do not insist that each glyph is followed by whitespace, and nor do
+we insist that glyphs do not contain whitespace. Our glyph dictionary
+can contain entries which are strict prefixes of other entries - that
+is, a glyph for (say) `v' which is the leftmost part of another glyph
+for (say) `w'. We resolve these ambiguities by taking the longest
+(widest) glyph which matches.
+
+So you should not be surprised if the program has matched the
+left-hand half of some letter and thinks it is a different letter. If
+the part that it did recognise does look like the letter in question,
+that isn't wrong. All you need to do is insert the whole of the
+actual letter in the dictionary - move the LH cursor to the start of the
+letter, and the RH cursor to its end, and hit `return' and enter the
+correct character. The longest match rule will mean it will prefer
+the entry you have just made.
+
+
+Matching context - Upper/Lower/Digit/Word dictionaries
+------------------------------------------------------
+
+We maintain separate dictionaries for the following types of glyph
+
+ Upper:
+ Upper case letters and ligatures starting with an
+ uppercase letter. Punctuation excluding `>'.
+ Lower:
+ Lower case letters and ligatures starting with a
+ lowercase letter.
+ Digit:
+ Digits and the greater than sign `>' (which can also
+ appear in the quantity field in the commodity display)
+ Word:
+ Words (or unambigous initial chunks of words) starting with
+ `l' or `I' - see the note, below.
+
+When you add an entry, you should add it to the appropriate dictionary
+for its matching context. You can do this by selecting the
+appropriate radiobutton or by pressing one of letters U D L W (the
+initial letters of the contexts) after moving the cursor to the
+appropriate spot but before hitting `Return' to enter the text for the
+new entry.
+
+
+Note regarding `l' and `I'
+--------------------------
+
+At the beginning of each cell in the table, we expect uppercase; in
+the middle of a word we expect lowercase; and, unfortunately, after an
+inter-word gap, we are not sure.
+
+This is troublesome because `l' and `I' look identical on the screen.
+So any time we see an unfamiliar word starting with `l' or `I', the
+program has to ask about it.
+
+After an interword gap, we first search for a Word entry in the
+dictionary. If there is a match we use it. Otherwise we search both
+the uppercase and lowercase dictionaries; if one matches and the other
+doesn't, or one matches a wider character than the other, we use it.
+If that fails to resolve the ambiguity we must ask.
+
+Don't try to make an entry in the character set dictionary mapping
+`vertical stick' to `l' or `I'. Instead, select the whole word (or
+enough of it that no different word would start with the other
+letter), and enter the whole thing as a new glyph in the Word
+dictionary.
+
+For example, in the supplied dictionary there is already a glyph for
+`Iron'; this is OK because there are no words which start `lron'.
+
+
+Short inter-word gaps
+---------------------
+
+It can happen that the problem you are being asked about is caused by
+the program failing to spot an inter-word gap and mistakenly thinks
+that the next word is necessarily in lowercase, so fails to recognise
+an uppercase letter. The context in which each glyph was recognised
+is shown on the screen, underneath the text which shows what it was
+recognised as.
+
+*You should check the alleged context before entering a character*.
+If it is wrong, you should fix it, rather that just making an entry
+in the wrong dictionary.
+
+When this happens, instead, make a new glyph for the last letter of
+the previous word plus the (unusually narrow) inter-word space, and
+end that entry with a literal space ` '.
+
+For example, you might find that `y<space>G' is treated as
+`y<??lowercase>' and the G doesn't get matched. Select the `y<space>'
+region of the bitmap and type `y ' into the string box.
+
+
+Overlapping characters - ligatures
+----------------------------------
+
+Some of the characters in the font used overlap with the next
+character. When this happens, select both the characters and enter
+them together as one glyph with a multi-character definition, as a new
+entry in the Lower or Upper dictionary.
+
+For example `yw' is rendered with the top right corner of the `y' and
+the top left corner of the `w' overlapping. This is dealt with by
+matching the whole merged thing - select the region of the screen
+containing `yw' and define it as `yw'.
+
+Such a combined entry - a ligature - is only needed if the letters
+cannot be separated at all. It's not needed if they merely abut.
+
+
+Fixing mistakes
+---------------
+
+The OCR query UI allows you to delete things from the local glyph
+dictionary. However you are not guaranteed to actually get an OCR
+query at all (and since it is not possible to override the presence of
+an entry in the master database with the absence of one in the local
+database). So this is not a reliable feature for being able to fix
+errors.
+
+If you think you have made mistakes answering OCR queries (for
+example, the recognised data is wrong), you should delete the file
+_local-char*.txt, which contains your local updates. It will then
+only use the centrally provided (and vetted) master file (which is
+automatically updated when you run the PCTB client, by default).
+
+It is also possible to have the OCR system reject particular strings.
+If you put a regexp in _local-reject.txt, any OCR result which
+matches this string will instead cause an OCR failure, invoking the
+OCR dictionary editor if appropriate. _master-reject.txt is the
+centrally maintained version of this file.
+
+Alternatively you can edit _local-char*.txt with a text editor. The
+format is not documented at the moment.
+
+
+Enabling interactive character set update
+-----------------------------------------
+
+Now that you have read this document, you should rerun your OCR job
+with the --edit-charset option. So run
+ ./ypp-commodities --edit-charset
+In future, this option is not usually needed, because it is the
+default if there is a local character set dictionary _local-<h>.txt
+for the relevant character height.
+
+With --edit-charset, when the OCR finds characters it does not
+understand, it will put up an OCR resolution query window. This will
+display the part of the text it is having trouble with, showing where
+it has got to, and allow you to edit the character set dictionary it
+uses for recognising the text.
+
+The process is subtle and it is important to understand the way the
+machinery works, and the possible mistakes you can make, before
+answering the program. So *Please read this documentation*, which
+explains the meaning of the entries you make.
+
+The character set updates you make will by default be submitted to my
+server so that they can be checked by me and shared with other users.
+See README.privacy.
+
+If you need help please ask me (ijackson@chiark.greenend.org.uk, or
+Aristarchus on Midnight in game if I'm on line, or ask any pirate of
+the crew Special Circumstances if they happen to know where I am
+and/or can get in touch).
~yarrgweb / ypp-sc-tools.web-live.git / blobdiff