JPGTN(2) Graphics Software JPGTN(2)NAMEjpgtn - create thumbnails of JPEG files
SYNOPSISjpgtn [options] file(s)OPTIONS-d <directory>
Specifies a directory to put the output file(s) in. If this
option is not supplied and the -S option is not in effect, it
defaults to the current directory.
-f Force overwrites of existing files when an output file already
exists.
-h Print a short usage message and exit.
-p <prefix>
Specify the filename prefix used for output files.
-q <quality>
Set JPEG quality setting for output file. The <quality> parame‐
ter is a number between 0 and 100. Effective range is probably
only between 15 and 90.
-s <size>
The default behavior of this switch is to specify the size of
the longest dimension of the output images in pixels. For
instance, a size of 75 would create a thumbnail of the original
image that would fit inside a 75 X 75 pixel box. The thumbnail's
length/width ratio will be the same as the original image's.
When used in conjunction with the -H switch or the -W switch,
this option specifies the height or width of the final thumb‐
nail. If this option is not supplied, or if it is not in the
allowable range (1-2048) the size defaults to 128. The allowable
range can be altered only prior to compiling.
-v Increase the verbosity level. This switch may be used multiple
times.
-H Specify that the thumbnail height should be the size specified
with the -s switch (see above.) In this case, the thumbnail
width is calculated by jpgtn and may be greater or lesser than
the size specified by the -s switch depending on the original
image.
-S Send output to STDOUT instead of file(s). If this option is sup‐
plied, the -p and -d options are ignored and jpgtn only pro‐
cesses the first file on the command line.
-W Specify that the thumbnail width should be the size specified
with the -s switch (see above.) In this case, the thumbnail
height is calculated by jpgtn and may be greater or lesser than
the size specified by the -s switch depending on the original
image.
-V Print the version and copyright banner and exit.
DESCRIPTION
Jpgtn creates small versions of pictures stored in JPEG format and out‐
puts these thumbnails either to STDOUT (for use with pipes, file redi‐
rection, or CGI scripts) or to the original filename with an optional
prefix. You may also specify a directory which you wish all the output
files to be written to.
Jpgtn writes one output file for each JPEG image file specified on the
command line. In order to be able to associate these output files with
the input files that they are generated from, jpgtn names them based on
the input filename. In order to avoid accidental overwriting of the
input files, jpgtn allows you to specify a prefix to prepend to each
input filename to construct the output filename. Jpgtn also allows you
to specify a directory to write the output files to. If no directory
and no prefix is specified, jpgtn writes the output files to the cur‐
rent directory using names constructed by prepending the default prefix
"tn_" to the input filenames.
If no prefix is specified, but a directory is specified, jpgtn will
write one file for each input file to the directory. The resultant
files will have the same filenames as the original images they were
generated from.
If no directory is specified, but a prefix is specified, then jpgtn
writes its output files to the current directory and names its output
files by prepending the supplied prefix to the filename of the original
image.
If both a directory and a prefix are specified, them jpgtn writes its
output files to the specified directory and prepends the supplied pre‐
fix to the original image's filename to construct the output file's
name.
The -S option forces jpgtn to write its output to stdout. If this
option is supplied, jpgtn ignores the -d and the -p options. This
option is useful if you want to take advantage of output redirection or
if you want to dynamically generate thumbnails for a CGI application.
The -s option gives you some control over the size of the thumbnails
that are generated. If you do not supply this option, a default size of
128 pixels is assumed. The number of pixels in the longest dimension of
a thumbnail generated by jpgtn will not exceed 'size' pixels. E.g. if
you supply this option with a parameter of 100 while making a thumbnail
of a 200x100 pixel image, the resulting image will be 100x50 pixels. If
the original jpeg is 200x200 pixels, the thumbnail will be 100x100, and
so on.
The -q option sets the JPEG quality level of the output JPEG file. This
defaults to 70, and although values between 1 and 100 inclusive are
allowed, I would suggest that 15 is probably as low as you can go with‐
out running into readability problems etc., and there isn't much point
going above 90. Also, note that quality level 100 is not lossless, nor
is the quality level a percentage. See the JPEG FAQ for further
enlightenment.
EXAMPLES
To create thumbnails of all the '.jpg' files in the current directory
and output them to the current directory with the default prefix "tn_"
use:
$ jpgtn *.jpg
To do the same thing as above, but to put the thumbnails in './thumbs'
use:
$ jpgtn-d "./thumbs/" -p "tn_" *.jpg
To create a thumbnail of the file image.jpg no larger than 75x75 pixels
and pipe it through the (hypothetical) program "jpegprog" use:
$ jpgtn-S -s 75 image.jpg | jpegprog
To create a thumbnail which has a width of 64 pixels and maintains the
original's height/width ratio from a file called foo.jpg use:
$ jpgtn-W -s 64 foo.jpg
To create a thumbnail which has a height of 64 pixels and maintains the
original's height/width ratio from a file called bar.jpg use:
$ jpgtn-H -s 64 bar.jpg
ACKNOWLEDGEMENTS
Thanks to the Independent JPEG Group for writing their useful and flex‐
ible JPEG software, without which this program could not use the
JPEG/JFIF file format.
Thanks to Willie Daniel who created gtnpic which this program is
derived from. Thanks to Russell Marks who created tnpic which was the
foundation for gtnpic and therefore the foundation of jpgtn as well.
Thanks to Terry Mackintosh for suggesting that there should be a way to
make jpgtn resize a specified dimension while allowing the other dimen‐
sion to float.
BUGS
Probably has some... if you find one please inform me at the address
below.
AUTHOR
Jeremy Madea <jeremymadea@mindspring.com>
SEE ALSO
xv (1), cjpeg (1), djpeg (1)"
Version 2.01 June 14, 2002 JPGTN(2)
