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| aformertransformer | hey all! Quick quetsion. If I have a file out.bin that stores just a byte sequence of LZW encoded text, can I decode this with ghostscript? | 17:38.32 |
| | I know LZWdecode is a thing, but I can't figure out how to load the file into gs and run the decode function on it | 17:39.07 |
| artifexirc-bot | <KenSharp> Yes, you need some PostScript | 17:59.35 |
| | <KenSharp> Firstly you need to allow Ghostscript to open the file on disk (this is the SAFER stuff) so you need to supply --permit-file-read=<filename> on the command line | 18:00.15 |
| | <KenSharp> Then you need to open the file with "(filename) (r) file" | 18:00.42 |
| | <KenSharp> which will leave a file object on the operand stack. | 18:00.50 |
| | <KenSharp> TO that you would apply the LZWDecode filter | 18:00.56 |
| | <KenSharp> If you wanted to supply an parameters to the LZWDecode you would supply them in a dictionayr, if not just push the filter name on the stack, let's assume no | 18:02.18 |
| | <KenSharp> So just /LZWDecode | 18:02.30 |
| | <KenSharp> That will again return a file object | 18:02.36 |
| | <KenSharp> At that point you just read from the file | 18:02.44 |
| | <KenSharp> Probably the easiest way to do this is something like : | 18:03.28 |
| | <KenSharp> /MyFile (filename) (r) file def | 18:03.28 |
| | <KenSharp> /MyFilteredFile MyFile /LZWDecode def | 18:03.29 |
| | <KenSharp> Then read in a loop:{MyFilteredFile 255 string readstring not {exit} if} loop | 18:05.53 |
| | <KenSharp> Then read in a loop:{MyFilteredFile 255 string readstring not {== flush exit} if ==} loop | 18:06.33 |
| | <KenSharp> If you want to write the output to a file instead of jjust printing it you'd replace the == with commands to write to a file | 18:06.50 |
| | <KenSharp> This is a program to do that, note you would need to permit file reading and writing on the relevant files: | 18:07.38 |
| | <KenSharp> /InFile (c:/tests/692779/image.lzw) (r) file /LZWDecode filter def | 18:07.38 |
| | <KenSharp> /OutFile (c:/tests/692779/image.bin) (w) file def | 18:07.39 |
| | <KenSharp> /Data 32768 string def | 18:07.40 |
| | <KenSharp> | 18:07.42 |
| | <KenSharp> { | 18:07.43 |
| | <KenSharp> InFile Data readstring { | 18:07.44 |
| | <KenSharp> OutFile exch writestring | 18:07.45 |
| | <KenSharp> } { | 18:07.47 |
| | <KenSharp> OutFile exch writestring | 18:07.48 |
| | <KenSharp> exit | 18:07.49 |
| | <KenSharp> } ifelse | 18:07.51 |
| | <KenSharp> } loop | 18:07.52 |
| | <KenSharp> | 18:07.53 |
| | <KenSharp> InFile closefile | 18:07.55 |
| | <KenSharp> OutFile closefile | 18:07.56 |
| aformertransformer | nice! Thanks for the detailed explanation. I'm going to give this a try now | 18:28.58 |
| | I'm getting `Error: /typecheck in --readstring--` ... do you think that means this isn't actually correctly formed LZW? | 19:38.11 |
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