pixautosize — determine if a file size or byte count is a standard image size
pixautosize
determines if a given file is one of the standard sizes used in the
BRL-CAD package, i.e. one of the sizes recognized by the
-a
option on
pix-fb(1).
If the dimensions are recognized, it prints a string suitable for use in
a Bourne shell
sh(1)
script to set the variables WIDTH and HEIGHT, e.g.
WIDTH=512; HEIGHT=512
The file name can be specified by using the
-f file_name
commandline option, or the file length (in bytes) can be
specified by using the
-l file_length
commandline option.
One of these two options must be present.
In either case, the
-b bytes_per_sample
option can be used to specify the number of bytes which are used
for each sample (pixel) in the file.
The default value is three (3), which is appropriate for use
with
pix(5)
files.
This should be changed to one with
-b 1
when processing a
bw(5)
file.
Similarly, the proper value for a
dbw(5)
file is 8 (1 channel of 8 byte samples),
and the value for
dpix(5)
files is 24 (3 channels of 8 byte samples).
These two examples both give the result of
WIDTH=50; HEIGHT=50;
the first could be for a bw(5) file and the second for a pix(5) file:
pixautosize -b 1 -l 2500
pixautosize -b 3 -l 7500
This example shows how to determine the size of a pix(5) file by giving the file name:
pixautosize -b 3 -f ../pix/moss.pix
with the result being
WIDTH=512; HEIGHT=512
This command can be used easily in shell scripts with a line like this:
eval `pixautosize -b 3 -f $FILE` # sets WIDTH, HEIGHT
For a major shell script which uses this program, examine pixinfo.sh(1) .
If the file or file_length specified does not match any of the standard sizes, one of these messages is printed on standard error:
pixautosize: unable to autosize nsamples=999
pixautosize: unable to autosize file '/dev/null'
In this case, the string printed on standard output is:
WIDTH=0; HEIGHT=0