PTrans scales and dithers an image while holding only 2 scanlines in memory at a
time.
This allows extremely large images to be processed using very little RAM.


PTRANS   Copyright (C) 2008  Paul Sheer  All rights reserved.

        -  www.protonet.co.za  -

usage: ptrans [-multiply W,H] [-scale W,H] [-input FILENAME] [-gamma F] [-s F]
                [-threshold N] [-grayscale] [-float] [-output FILENAME]

Produces PBM (i.e. P4) dithered output, or PGM (i.e. P5) gray-level output
from PPM or PGM (P5 or P6) input.
Reads/writes from/to stdin/out if -input/-output not specified

        -multiply  makes bigger dots (try -multiply 3,3),
        -scale  sets output width and height in pixels using linear
interpolation.
        -gamma  adjusts brightness F range 0.2 to 5.0
        -s  use S curve color adjustment F is gamma value of 0.2 to 5.0.
                Good for contrast adjustment. -s 1000.0 is equivalent to
-threshold 32768
        -threshold  clips N range 0-65535
        -float  floating point interpolation
        -grayscale  output P5 gray-level file, 1 byte per pixel

Example: some HP printers can be used as an A4 photostat machine
in combination with a scanner:

scanimage -x 210 -y 297 --resolution 300 | \
   ptrans -scale 3307,7014 -multiply 3,1 -s 1.2 | \
   foo2xqx -g 9921x7014 -u 50x0 -r1200x600 -p9 -m1 -n1 -d1 -s7 -J  -U  -D0 \
 > /dev/usblp0

PERMISSION  UID  GID    PACKED    SIZE  RATIO METHOD CRC     STAMP     NAME
---------- ----------- ------- ------- ------ ---------- ------------ ----------
[generic]                12330   39460  31.2% -lh5- c155 May 31  1980 ptrans
[generic]                  873    1597  54.7% -lh5- 6f6c May 31  1980 ptrans-mos.readme
[generic]                 5018   23565  21.3% -lh5- 4ebe Aug  3  1980 ptrans.c
---------- ----------- ------- ------- ------ ---------- ------------ ----------
 Total         3 files   18221   64622  28.2%            May 31 21:10