I've been able to OCR letter-quality printer output to 97% (mostly Os and Xs problems).
But it seems that machine-learning text-recognition is also now biased to reject computer code because it doesn't look like human language.
> With less-than-satisfactory OCR output, I resorted to a process I used many years ago when converting scans made of old Commodore ROM dumps printed on a Commodore 1515 dot-matrix printer. The process relies on the ASCII OCR output having the same repetitive errors. "B" and "8", "S" and "5" are good examples, as are "l" and "1", and "O" and "0". There are many other similar single-character errors and, when working with x86 code, there are similar errors with instructions like "MOV". This process naturally works better if the output file is monolithic rather than single-page OCR conversions because you can do substitutions across the entire converted printout and not 75 separate files.
> The next formatting hassle was the spacing. This required repetitive substitutions of a descending numbers of spaces to tabs (i.e., replace 8 spaces with a tab, 7, 6, etc.). Then if you want to return it to fixed spaces (which is likely how the original printer printed it -- spaces and not vertical tabs), you can. For pure re-creation work, spaces produce absolute column formatting while tabs can move around depending on the program displaying the file.
> Once you run thought the 15 or so common global substitutions and tab conversion, it's a lot easier to work with the file to fix formatting and perform other cleanup. This is then followed by a line-by-line comparison against the original printouts. Overall I'd say the conversion output quality with this method is very good.
I've got a 4" stack of wide-carriage COBOL. I guess it's two revisions of the same system so I only need to scan the newer half. Its probably from a TI Omni 810.
On the other hand, I've got 100 pages of code printed in compressed font by someone wanting to make sure that 80+ char lines fit within margins. So a lot of words just don't come out at all. A frequent error is "A" becomes "H", "O" becomes "U" because the top dots aren't "attached".
And columns of line numbers starting with 0001, or hex? The most confounding thing is OCR that thinks 00 is a sideways 8, and that dominates the uniform block, so it tries to interpret the whole column as sideways text. In another situation, it interprets two stacked lines (each starting with 0) as one line starting with 8 and it just goes off the rails.
So I've been working with automatic skew correction, then clipping it into rows, in order to get each line of text isolated from the surrounding context. When I do that, I get better results, but it is not great either.
I'm considering going all-in on training a new recognizer on snippets. For that, I'll be constructing "The Set of All As" and so on.
I might do what you said, column sensitive. A first-pass assembler which does spell checking and makes the corrections. M0V is a single replacement on MOV, MOV8 is closest to MOVB. For registered, R Oh must be R zero. But R Oh will be valid as a symbol name (curse your poor choice of symbol name). Alas, R1 is defined in the symbol table as a mnemonic for 1.
This idiom occurs in TMS9900 assembly (of which I have 2100+ pages to scan)
Indexed addressing into caller's register file: MOV @R1*2(R13),R0
Where R1 is 1, a small offset in #words so the operand is pointer to the word after where R13 points. Yet @RI(R13) is valid if RI is in the symbol table.
So there has to be some heuristic that starts at "is RI a defined symbol?" "Can a symbol be used in this context?" Yes/Nope: it is probably R1.
And R11 is used a lot.
Same curse on people who used I as a counter variable in type-in programs. Countless folks typed it as a 1 in expressions before magazines got better fonts.