batch resizing photos for web... linux to the rescue!

Just though I would share a mini success...

Same old problem every time I want to post some images to the web I have
to reduce the size of the image. This can become tedious using the canon
zoom browser for more than a few images.

A quick bit of research and I discovered that I already had the tools to
help on my linux box, but that suits me just fine I have a samba
share to my linux machine so i just draged the images over using M$
explorer. Once there a few commands later and I have my scaled images.

The programs needed are 'djpeg', 'pnmscale' and 'cjpeg' the great thing
is that using these command line tools is so flexible, I can scale 1 or
1000 images just as easily.

The 'djpeg' command converts a jpeg image to a PNM file and 'cjpeg' does
the reverse. The 'pnmscale' command does exactly what you would think it
can reduce or enlarge a 'pnm' image.

So to achieve a 75% reduction all you have to do is string the three
filters together like so:-

djpeg largefile.jpg | pnmscale '0.25' | cjepg > smallfile.jpg

Thats all well and good, the source file remains untouched and a new
small image is created, but we can make things easier still.
Its a pain to type the source and destination filenames especially if
you want to convert more than a few files.

So all we do is embed these commands in a few lines of shell script and
I can scale as many images as I want automaticaly reading and creating
file names:-

mkdir small
ls *jpg|while read F
do
echo "scaling $F"
djpeg $F|pnmscale '0.25'|cjepg >small/$F
done


Job Done!! I now have a folder called 'small' filled with the reduced
images.

Along with 'pnmscale' there are other acompanying filters which I have
yet to try 'pnmstrech', 'pnmflip', etc

Tom

 

Or, if you want to stick within Windows, simply download and install the
freeware program EasyThumbnails from http://www.fookes.com/ezthumbs/ and it
will do everything you just described with an easy to use graphical
interface. If you choose to use the lanczos3 algorithm and add a little
sharpness (both selected from within the settings menu), you'll be amazed at
the quality of images it produces. You can batch process all images in a
directory, tell it to create the output directory you specify, have it
rename the newly created files based on incremental additions to the
existing filename, and specify the maximum pixel dimension allowable in
either axis while still maintaining the proper aspect ratio.

 

There's no need to convert them to pnm and back to jpg, you can
manipulate jpgs with convert (google for ImageMagik).

I wrote some tiny scripts to reduce jpegs, rotate, rename as sequence,
and so on...

You can even use scripts from the console or from Konqueror, or even
GQView (that's my choice to view, organize, manipulate images

I love the flexibility that command line gives you doing such things...

-Quercus-

Tombo escribió:

 

A quick bit of research and I discovered that I already had the tools to

No need to wake up linux to do that - the tools are available for Windows
(at least djpeg and cjpeg are...).

Cheers,
David

 

You don't even need to use pnmscale for this purpose, as djpeg has a
built-in rescaling option (look at its "-scale" option) which makes
the process much more efficient. The choice of rescaling factors is
limited though, to values 1/2, 1/4, and 1/8.
More options are available with my improved versions (currently unofficial
forks of original library, will probably go in next official version):

http://jpegclub.org/djpeg/
http://jpegclub.org/cjpeg/

The tools are also available for other systems (Windows etc.).

Regards
Guido

 

While this works fine, I recommend you go find a copy of ImageMagick
and use it's "convert" command for stuff like this---it's a lot more
versatile and feature-rich.

 

Thanks all for your comments, as always there is more than one
way to skin a cat. I did look at down loading a windows tool
for the job, but there are so many, and I just will not install any
old software on my windows pc anymore. My start menu is already
bigger than than it should be. I find it best to keep just the
software I use on my PC. So trying out a few different packages
to find a good one is not attractive.
The point i was trying to make was that i had the tools already
on my linux box no download needed.
I think I will try imagemagic tho probably on linux as thats where
my webserver lives.

tom