Pamflip User Manual(0) Pamflip User Manual(0)NAMEpamflip - flip or rotate a PAM or PNM image
SYNOPSISpamflip { -leftright | -lr | -topbottom | -tb | -transpose | -xy |
-rotate90 | -r90 | -cw | -rotate270 | -r270 | -ccw | -rotate180 | -r180
-null | -xform=xform1,xform2... } [-memsize=mebibytes] [-page‐
size=bytes] [pamfile]
All options can be abbreviated to their shortest unique prefix. You
may use two hyphens instead of one to designate an option. You may use
either white space or an equals sign between an option name and its
value.
DESCRIPTION
This program is part of Netpbm(1).
pamflip flips a PAM or PNM image top for bottom or left for right, or
transposes it horizontal for vertical, or rotates it 1, 2, or 3 quarter
turns.
To rotate at other angles, use pnmrotate. It is much slower, though.
The input image is pamfile, or Standard Input if pamfile is not speci‐
fied.
To flip/rotate a JFIF (JPEG) image losslessly, use jpegtran. jpegtran
is part of the Independent Jpeg Group's compression library package,
not part of Netpbm. The normal Netpbm way to flip a JFIF file would be
to convert it to PNM, use pamflip, and convert back to JFIF. But since
JPEG compression is lossy, the resulting image would have less quality
than the original. jpegtran, on the other hand, can do this particular
transformation directly on the compressed data without loss.
OPTIONS
You must supply exactly one of the following options:
pamflip's predecessor (before Netpbm 10.7 - August 2002) pnmflip did
not have the -xform option and instead allowed you to specify any num‐
ber of the other options, including zero. It applied all the indicated
transformations, in the order given, just like with pamflip's -xform
option. (Reason for the change: this kind of interpretation of options
is inconsistent with the rest of Netpbm and most of the Unix world, and
thus hard to understand and to implement).
-leftright
-lr Flip left for right.
-topbottom
-tb Flip top for bottom.
-transpose
-xy Transpose horizontal for vertical. I.e. make the pixel at (x,y)
be at (y,x).
-rotate90
-r90
-ccw Rotate counterclockwise 90 degrees.
-rotate180
-r180 Rotate 180 degrees.
-rotate270
-r270
-cw Rotate counterclockwise 270 degrees (clockwise 90 degrees)
-null No change. (The purpose of this option is the convenience of
programs that invoke pamflip after computing the kind of trans‐
formation desired, including none at all).
This option was new in Netpbm 10.13 (December 2002).
-xform=xform1,xform2...
Apply all the transforms listed, in order. The valid values for
the transforms are as follows and have the same meanings as the
identically named options above.
· leftright
· topbottom
· transpose
This option was new in Netpbm 10.13 (December 2002).
The following options help pamflip use memory efficiently. Some flip‐
ping operations on very large images can cause pamflip to have a very
large working set, which means if you don't have enough real memory,
the program can page thrash, which means it takes a ridiculous amount
time to run. If your entire image fits in real memory, you don't have
a problem. If you're just flipping top for bottom or left for right,
you don't have a problem. Otherwise, pay attention. If you're inter‐
ested in the details of the thrashing problem and how pamflip
approaches it, you're invited to read a complete explanation in com‐
ments in the source code.
-memsize=mebibytes
mebibytes is the size in mebibytes (aka megabytes) of memory
available for pamflip. It is the lesser of the amount of real
or virtual memory available.
pamflip does nothing special to allocate real memory or control
it's allocation -- it gets whatever it gets just by referencing
virtual memory normally. The real memory figure in question is
the maximum amount that pamflip can be expected to end up with
by doing that. This is just about impossible for you to know,
of course, but you can estimate. The total real memory in your
system should be a major factor in your estimate.
If pamflip cannot fit the entire image in the amount of memory
you specify, it does the transformation in chunks, using tempo‐
rary files for intermediate results.
Strict horizontal transformations (either left for right or
null), pamflip never keeps more than one row in memory, so the
memory size is irrelevant and pamflip doesn't use temporary
files.
The real memory is important when you do a column for row type
of transformation (e.g. -rotate90). In that case, even if pam‐
flip can fit the entire image in virtual memory at once, if it
does not also fit in real memory, the program will thrash like
crazy because of the order in which pamflip accesses the pixels,
and that means it will take a ridiculously long time to run. A
proper -memsize drastically reduces the paging.
If you specify -memsize too large, pamflip may attempt to get
more virtual memory than the system allows it and fail. If it
can get the virtual memory, but -memsize is larger than the
amount of real memory the system allows it and the transforma‐
tion is row for column, it will page thrash and run very slowly.
A value even slightly too high is the same as infinity.
If you specify -memsize too small, the program will run slightly
more slowly due to extra overhead in manipulating temporary
files. Also, if your environment isn't set up to make temporary
files possible, pamflip will fail.
Doing the entire transformation 'in memory' doesn't speed things
up as much as you might think, because even with the temporary
files, the data is just as likely to be in memory. Virtual mem‐
ory gets paged to disk and disk files get cached in memory. In
fact, the pixels fit much more compactly into memory when stored
in a temporary file than when stored 'in memory' because pamflip
uses a more efficient format. So you're likely to have less
disk I/O when you allow pamflip less memory.
If you do not specify -memsize, pamflip assumes infinity.
This option did not exist before Netpbm 10.7 (August 2002).
Before Netpbm 10.42 (March 2008), this option applied only to
real memory. pamflip would always keep the entire image in vir‐
tual memory and if it could not get enough virtual memory, it
failed. pamflip accessed the pixels in an order designed to
keep real memory use within the specified amount.
-pagesize=bytes
bytes is the size in bytes of a paging unit -- the amount of
memory that gets paged in or out as an indivisible unit -- in
your system. The default is 4KiB.
This option has no effect.
Before Netpbm 10.42 (March 2008), pamflip used it to control its
use of real memory.
This option did not exist before Netpbm 10.7 (August 2002).
Miscellaneous options:
-verbose
This option causes pamflip to issue messages to Standard Error
about its progress.
SEE ALSOpnmrotate(1), pnm(1), pam(1), jpegtran manual
HISTORYpamflip replaced pnmflip in Netpbm 10.13 (December 2002). pamflip is
backward compatible, but also works on PAM images.
AUTHOR
Copyright (C) 1989 by Jef Poskanzer.
netpbm documentation 20 January 2008 Pamflip User Manual(0)
