using make to convert images to thumbs

[Jason Stephenson]

Python wrote:
> I have a client that laid out their images and thumbs into almost
> parallel directory structures.
> 	/img		/thumb
> 	  /x		  /img
> 	    /y		    /x
> 	      /*.jpg	      /y
> 			        /*.jpg
> 
> x and y are two digit directory names used to shorten the directory
> scans to retrieve files.  I thought I could use a Makefile to automate
> the creation of thumbs, but this pattern has me stumped.

How so? It is very straightforward. I'd put the Makefile in the /img 
directory or just above it. Your target to make the thumbnails would run 
whatever program makes the thumbnails with the appropriate options.

If you needed different target directories, you could specify them in 
the environment and on the command line. BSD make makes this trivial and 
I'm pretty sure that GNU Make works about the same.

Here's an example:

The Makefile:

## Makefile example starts here. ##
IMG_BASE = /img
THM_BASE = /thumb/img

IMG_PROC = /path/to/image/processor
IMG_PROC_OPTS = # default options for image processor

TARGET = # undefined. define on command line

thumbs:
	if test "${TARGET}" = "" ; then
		echo "TARGET undefined"
	else
		${IMG_PROC} ${IMG_PROC_OPTS} ${IMG_BASE}/${TARGET} \
		${THM_BASE}/${TARGET}
	fi
## Makefile example ends here. ##

Then, on the command line, you might run:

$ make thumbs TARGET=x/y

The above should work with BSD make, and I'm 90% certain that it will 
work with GNU make, as well. It might require a little massage to 
actually do anything useful.

> 
> I am going to just write a script to step through the source tree and
> check the corresponding time stamp unless someone offers a suggestion.
> (No they will not shuffle things around because they have lots of logic
> in place.)

That would work if you have it run periodically and just make thumbs for 
new files, or files that have changed. My example above could be used to 
do entire subdirectories at once.

If you know much about make, there are ways to make the above fancier 
and more bulletproof. For instance, you might want to have IMG_PROC_OPTS 
be added to what is specified in the environment rather just being 
hardcoded in the Makefile or completely overridden by the command line 
environment. This would make it easier to have slightly different 
options on a given run.

Also, if you need to specify filenames or globs to the IMG_PROC, you can 
do that as part of your target. My assumption above is that the IMG_PROC 
can take directories as targets and processess everything in 
them.--Perhaps it is a script.

Along the same lines, a fancier solution would run a shell loop over the 
files in the TARGET directory, and process each one with IMG_PROC if you 
don't have a script to do everything in a directory in one go.

HtH,
Jason