Why does ImageMagick border gravity always go north instead ofsouth for captions?

I'm trying to caption all the pictures in a directory.
The first step is adding white space to the bottom.
The alias below works, but it puts the 200-pixel white
space at the TOP of the picture every time, no matter
whether I have the "gravity" option set to "north" or
"south".

I actually want the caption on the bottom! (south).

What's wrong with my alias that the captions always
end up on the north side?

Any suggestion?

alias caption='for f in *.{jpg,gif,JPG,GIF,jpeg,JPEG,png,PNG};do convert $f -splice 0x200 -gravity south -bordercolor white white_$f; mv white_$f $f;kolourpaint $f; done'

 

Try putting the
-gravity south
option /before/ the
-splice 0x200
option, as in
convert $f -gravity south -splice 0x200 -bordercolor white white_$f

 

That worked!

Now how the heck did you know that would work?

There was no error message with my method.
But, mine put the gravity north no matter what.
Yet, yours put gravity south.

How did you know that the options were order dependent?

 

http://www.imagemagick.org/script/command-line-options.php#gravity
contains a hint about this "If gravity is applied before..."

?There should be no error in your method since it appears that it is
correct-- it changes the gravity for any following commands.
Ie, had you now had a command after your "gravity" command, it would
have shifted it. It did not know you wanted to apply it to the prior
command.

 

I followed the documentation...

convert(1) ("man 1 convert") says
NAME
convert - convert between image formats as well as resize an
image, blur, crop, despeckle, dither, draw on, flip, join, re-sample,
and much more.

SYNOPSIS
convert input-file [options] output-file

OVERVIEW
[snip]
For more information about the convert command, point your browser
to file:///usr/share/doc/ImageMagick-6.4.3/www/convert.html or
http://www.imagemagick.org/script/convert.php.

And http://www.imagemagick.org/script/convert.php says
-splice geometry splice the background color into the image

And, the link on "-splice"
(http://www.imagemagick.org/script/command-line-options.php#splice) says
This will add rows and columns of the current -background color into the
given image according to the given -gravity geometry setting. >See Image
Geometry for complete details about the geometry argument.

From that, it became apparent (to me, at least) that you had to set
the -gravity first, so that -splice wouhd have a "given -gravity geometry
setting".

BTW, you want -background <colour>, not -bordercolor <colour>, and
the -background option should precede the -splice option, just like
the -gravity option did.

Gravity defaults to north.
Actions are executed sequentially, so the -splice option is
executed /before/ the -gravity option in your original commmandline.

I simply had you put an overriding -gravity option /before/ the -splice.

Many commands have order-dependant options, so it is one of those things you
look for. And, the documentation on -splice implied the dependence on
order. So, that's what I tried.

And, for what it's worth, I actually tried (for real) a number of
combinations before coming up with one that worked.

 

Thanks to your astute advice, here's the current alias that I'm using:
alias caption='for f in *.{jpg,jpeg,gif,png,JPG,JPEG,GIF,PNG};do convert $f -background white -gravity south -splice 0x200 tmp_$f; mv tmp_$f $f;kolourpaint $f; done'

That alias:
a) Finds all pictures in the current directory, and,
b) Sets the color to white for the background to be added, and,
c) Sets the location of the splice to be south (i.e., bottom), and,
d) Adds a 200-pixel splice to the bottom of the picture (for captions), and,
e) Saves the file, and then moves the file to the original name, and,
f) Then opens up Kolourpaint which adds the actual desired caption.

I find this useful to send batches of pictures to friends and
family where *each* picture is annotated with the ad hoc storyline.

Any improvements to the alias are *always* welcome!

 

Personally, I'd recommend writing a function for this sort of thing.

 

I've written (long ago) Fortran functions.
Do you mean to suggest a c program that does this?

 

No, a shell function. It's somewhat similar to an alias, but more
flexible. Among other things, you can define local variables inside a
function. An example follows.

my_function()
{
for i in *
do
some_command_here
some_other_command_here
done

if [ some_condition ]
then
some_command_here
some_other_command_here
else
yet_another_command_here
fi

exit 0
}

You can write lots of functions like that and /source/ them from your
shell initialization file - e.g. ~/.bashrc - or from another file. For
instance, you can have a file ~/.myfunctionsrc and then in your
~/.bashrc you have a line like...

source $HOME/.myfunctionsrc

 

My bad. I'm used to writing functions for use inside of scripts, which
are of course normally executed within a subshell. ;-)

That would work, of course, but I think it may be cleaner to have a
separate, modular file for that, just in case .bashrc ever gets
overwritten. ;-)