X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~yarrgweb/git?a=blobdiff_plain;ds=sidebyside;f=yarrg%2FREADME.charset;fp=yarrg%2FREADME.charset;h=65aa51aee70e1cf85be1be3229ed8d3dd54df4cb;hb=c68fb80a6bbf7acbcac4b2cb2143f5fea745cd2b;hp=0000000000000000000000000000000000000000;hpb=b9cce976550d000f15e5a8f2b690740bdae1e468;p=ypp-sc-tools.web-live.git diff --git a/yarrg/README.charset b/yarrg/README.charset new file mode 100644 index 0000000..65aa51a --- /dev/null +++ b/yarrg/README.charset @@ -0,0 +1,185 @@ +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 `yG' is treated as +`y' and the G doesn't get matched. Select the `y' +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-.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).