saper / studycapt

Studies in implementing support for CAPT printers

studycapt

Welcome to the Studies In Implementing Support for CAPT Printers!

This is just a repository for miscellaneous experiments, tools and tips dedicated to an ongoing goal of implementing a superior^® alternative driver for CAPT-only Canon laser printers.

Here's a rundown on what's in here:

docs (Docs and Notes)

First and foremost, this is the place for study notes documenting research on CAPT printers, improvement of captdriver, test procedures and other miscellaneous information.

capt.lua (CAPT/USB Dissector for Wireshark)

A Lua dissector which annotates CAPT commands in packet captures in Wireshark.

To use the dissector for a single Wireshark session, run this command in a directory containing capt.lua:

$ wireshark -X lua_script:capt.lua

Other ways of adding Lua dissectors are explained in Chapter 10 of the Wireshark Developer Guide.

The dissector currently only dissects packets over USB. CAPT over Ethernet and parallel printer/IEEE 1284 ports are currently not supported.

captstream.py (CAPT Job File and Stream Toolkit)

A Python module to extract data from CAPT job files or streams that contain or transport print data for/to print devices.

This module may be run as a command, like in this Unix-like shell example:

./captstream.py extract --page=1 --out_file=output_file.pbm input_file.capt

If on Microsoft Windows, try python captstream.py extract --page=1 --out_file=output_file.pbm input_file.capt in cmd.exe.

To use standard output, just skip --out_file:

# WARNING: Ordinary files will be overwritten without warning
./captstream.py extract --page=1 input_file.capt > output_dest

To use standard input, use a single hypen - as the input file path. The --num_pages option sets the number of pages to process.

The following example contains a complete pipeline from Ghostscript to captfilter to captstream.py:

# Extract pages 1 to 10 from a PDF, prepare a CAPT 1.x raster then
# decompresse the raster. Multiple PBM files will be written, each
# containing a single page.
# Page numbers will be inserted before the last ASCII full stop '.'
# (U+002E) in the output path specified by --out_file, or as a
# suffix if there is no full stop.
# The command can take a long time to complete, a process monitor
# can be improvised as a status monitor. Check the CPU and RAM
# usage for gs, captfilter and python.
# If the command freezes, try pressing CTRL-D.
# Multiple attempts at this command may be required for some pages
# on some systems.
gs -r600 -dSAFER -dNOPAUSE -dNOPROMPT -sDEVICE=pgmraw -sOutputFile=- example.pdf |\
captfilter --CNTblModel=0 --Resolution=600 |\
./captstream.py extract --num_pages=10 --out_format=p4 --out_file=example.pbm -

PROTIP: Reduce the 600 in -r600 to a smaller number, like 150, as a quick and dirty way to reduce oversize pages.

in2pbmp4.sh (Input to PBM P4 Image Script)

A script originally created to help visualise arbitrary data as a PBM P4 image. Currently obsolete and due for an improvement. For now a printf and a dd is probably more usable:

# Example for 200x200 1bpp image
printf "P4\n200 200\n" > example.pbm
dd if=input.bin bs=$((200 * 200 / 8)) count=1 >> example.pbm   # PROTIP: '>>' for appending, NOT '>'

The format is like:

printf "P4\n200 200\n" > $OUTPUT_FILE
dd if=$INPUT_FILE bs=$((200 * 200 / 8)) count=1 >> $OUTPUT_FILE

Try /dev/urandom as an input file for a start!

If you are still interested in how to use this script, please checkout versions 58c6e3c of the Studycapt source tree or earlier.

sample_balls.py (Performance Test Page Generator)

A Python script to generate test pages of varying complexity in SVG format, in order to test rasteriser and compressor performance.

# Generate an A4-sized page filled with 16x16 grey ellipses
$ ./sample_balls.py --size a4 --balls-per-row 16 --mode grey > test_a4_grey.svg

# Generate a US Letter-sized page filled with 2x2 gradient-filled ellipses
$ ./sample_balls.py --size letter --mode bw-radial-gradient > test_letter_grads.svg

Run ./sample_balls.py --help for a list of options.

Pages with a few grey ellipses are simple and therefore easy to process, while pages filled with thousands of radial gradient-filled ellipses pose a formidable challenge at larger sizes and higher resolutions.

sample_blots.py (RLE Test Page Generator)

A Python script to generate images for analysis of RLE algorthms. This script was originally created to study the Smart Compression Architecture (SCoA) algorithm used by select late-1990s and early-2000s Canon laser printers. It may be used for analysing other RLE codecs as well.

PBM P4 and PGM P5 output formats are supported.

# Generate a 1-bit, 600dpi A4-sized image with pixel runs of different length
$ ./sample_blots.py --mode mirrored-incr-runs --size=a4 --resolution 600 --format p4 --out_file test.pbm

# Alternative example using stdout
# (WARNING: ordinary files will be overwritten without warning)
$ ./sample_blots.py --mode mirrored-incr-runs --size=a4 --resolution 600 --format p4 > test.pbm

Run ./sample_blots.py --help for a list of options.

scoa.py (SCoA Toolkit)

A Python module containing a SCoA decompressor and other utilities for decompressing SCoA images or print data. The decompressor should work, but has not yet been thoroughly validated.

See also Issue #33 on the original captdriver repo for details.

from scoa import SCoADecoder

# Create decoder object for a 596-byte wide bitmap & decode test file
decoder = SCoADecoder(596)
with open('captfile.capt', mode='rb') as cf:
    image_bytes = bytes(decoder.decode(x for x in cf.read()))

Have fun!

Licensing

Licensing terms may vary between files in this repository, as it may contain copy-pasted material licensed by other authors.

Please check individual files for licensing terms and conditions, if you wish to use any code or information in this repository in your own work.

Links

If you are looking for the libre open-source CAPT driver:

• Alexey Galakhov's original captdriver repository

  • My version

Other stuff:

• The unofficial Captdriver Wiki!

• Alexey's CAPT reverse-engineering "scratch repo"