Provided by: netpbm_11.08.02-1_amd64 
NAME
pamflip - flip or rotate a PAM or PNM image
SYNOPSIS
pamflip { -leftright | -lr | -topbottom | -tb | -transpose | -xy | -rotate90 | -r90 | -cw
| -rotate270 | -r270 | -ccw | -rotate180 | -r180 -null | -xform=xform1,xform2... }
[-memsize=mebibytes] [-pagesize=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 specified.
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
In addition to the options common to all programs based on libnetpbm (most notably -quiet,
see
Common Options ⟨index.html#commonoptions⟩ ), pamflip recognizes the following command
line options:
Specifying the Transformation
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 number 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 transformation 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).
Memory Management
The following options help pamflip use memory efficiently. Some flipping 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 interested in the details of the thrashing
problem and how pamflip approaches it, you're invited to read a complete explanation in
comments 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 temporary files for intermediate results.
In strict horizontal transformations (left for right) or the null transformation,
pamflip never keeps more than one row in memory, so the memory size is irrelevant
and pamflip doesn't use temporary files.
In strict vertical transformations (top for bottom), even when you allow pamflip
enough memory to keep the entire image in virtual memory, it accesses it in a
single pass, which does not cause any thrashing; the chunks in temporary files thus
don't help.
The real memory is important when you do a column for row type of transformation
(e.g. -rotate90). In that case, even if pamflip 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
transformation 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
because of 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 memory 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 virtual 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
-verbose
This option causes pamflip to issue messages to Standard Error about its progress.
SEE ALSO
pnmrotate(1), pnm(1), pam(1), jpegtran manual
HISTORY
pamflip 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.
DOCUMENT SOURCE
This manual page was generated by the Netpbm tool 'makeman' from HTML source. The master
documentation is at
http://netpbm.sourceforge.net/doc/pamflip.html