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. *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* 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). Recognition algorithm --------------------- We recognise the text in the commodity screen by doing exact matching of `glyph' bitmaps, against the bitmap 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 database 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 database - 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 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 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. 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 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). 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 for the uppercase letter in the lowercase database. 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). For example, you might find that `yG' is treated as `y' and the G doesn't get matched. Select the `y' region of the bitmap and type `y\x20' into the string box. Sorry for this rather poor UI! 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. 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'. 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. 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 Send me your updates -------------------- 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 :-).