-Character set query tool, and semantics of the glyphs
------------------------------------------------------
-
-Sometimes the OCR will not be able to recognise some text and you will
-have to help it out. It will display the part it is having trouble
-with, showing where it has got to, and allow you to edit the character
-set database it uses for recognising the text.
+Handing OCR failures
+--------------------
-*This is subtle* and it is important to understand the way the
-machinery works, and the possible mistakes you can make, before
-answering the program. *Please read this documentation*
+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.
-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).
+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
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 database
+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
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 database - move the LH cursor to the start 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.
Upper vs lower case - important note regarding `l' and `I'
----------------------------------------------------------
-We maintain separate databases for upper and lower case. At the
+We maintain separate dictionaries for upper case (Upper), lower case
+(Lower), and (initial portions of) mid-phrase words (Word). 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.
So any time we see a word starting with `l' or `I', the program has to
ask about it.
-*Do not* make an entry in the character set database mapping `vertical
-stick' to `l' or `I'. Instead, select enough of the whole word in
-question that no word would start with the other letter, and enter the
-whole word or part of it as a new glyph.
+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.
-For example, in the supplied database there is already a glyph for
-`Iron'; this is OK because there are no words which start `lron'.
+*Do not* make an entry in the character set dictionary mapping
+`vertical stick' to `l' or `I'. Instead, select enough of the whole
+word in question that no word would start with the other letter, and
+enter the whole word or part of it as a new glyph as a new entry in
+the Word dictionary.
-Do not make an entry for a string more than 7 characters long;
-currently we cannot cope (and you'll have to remove it manually from
-the charset-15.txt file).
+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
*You should check the alleged context before entering a character*.
If it is wrong, you should fix it, rather that just making an entry
-for the uppercase letter in the lowercase database.
+for the uppercase letter in the lowercase dictionary.
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
-\x20 (yes, type \ x 20).
+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\x20' into the string box.
-Sorry for this rather poor UI!
+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.
+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
Fixing mistakes
---------------
-The OCR query UI allows you to delete things from the glyph database.
-However since you are not guaranteed to actually get an OCR query at
-all if the database contains errors, you shouldn't rely on this.
+The OCR query UI allows you to delete things from the glyph
+dictionary. However since 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), if the dictionary contains errors, you shouldn't
+rely on this.
If you think you have made mistakes answering OCR queries (for
-example, the recognised data is wrong), you should download a fresh
-copy of charset-15.txt from
- http://www.chiark.greenend.org.uk/~ijackson/ypp-sc-tools/master/pctb/charset-15.txt
+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).
-Send me your updates
---------------------
+Enabling interactive character set update
+-----------------------------------------
-The character set is in the file `charset-15.txt'. When you enter new
-characters, they are added there. If you do this, please email me
-your charset file (ijackson@chiark.greenend.org.uk) so that I can
-include your contributions in future versions. This will also let me
-check that they seem right :-).
+Now that you have read this document, you should rerun your OCR job
+with the --edit-charset option. You probably want to supply --same as
+well, to avoid having to wait for it to page through and recapture all
+the screenshots. So, this time,
+ ./ypp-commodities --edit-charset --same
+and in future, just always run it with the --edit-charset option.
+
+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.
+
+Be sure to check or specify the dictionary to which the new glyph
+should be added. Normally the default will be the Word dictionary
+which is right if the match failure is a new word starting with l or I
+(see above). You will need to change this to the Upper or Lower
+dictionary for new ligatures. You should not need to add new Digits.
+
+Also, 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