Saturday, 24 October 2009

Bulk Photo Scaler

After my holiday I captured hundreds of photos. I want to upload some of them to my online photo album. Before uploading the photos I need to scale the photos to a smaller size to speed up the file transfer and save my internet bandwidth. A popular bulk image processor - BIMP can be found from Cerebral Synergy.

I have some pretty unique requirements to bulk scale these photos. They have been captured using different cameras - N95, XM5800, Canon, Olympus, Pentax, etc. - each having different image resolutions and therefore sizes. So I cannot just apply a single factor to all the pictures. Also, I have some panorama pictures shot with Panoman which are very wide. So I cannot apply a single size to all pictures - I need to keep the aspect ratio. I decided to write a little bulk image scaler myself.

The basic image resizer is pretty simple using Java:

 BufferedImage File(fileName));
 int w=(int)(img.getWidth()*factor);
 int h=(int)(img.getHeight()*factor);
 String imageType=getFileSuffix(fileName);
 Image scaledImg=img.getScaledInstance(w, h, Image.SCALE_DEFAULT);
 BufferedImage bi=new BufferedImage(w, h, img.getType());
 bi.createGraphics().drawImage(scaledImg, 0, 0,null);
  new File(newFileName));

It is not the most efficient way to do this but it is simple and works. To keep aspect ratio is simply a matter of using the new width and the original picture's aspect ratio to calculate the new height:

 double ratio=(double)img.getHeight() / img.getWidth();
 int h=(int) (ratio*w);

The full source code is and It still needs some refactoring and cleaning up. The usage of the utility:

Usage: java directory_name [-f scale_factor] | [-s w
h] | [-k w]
-f scale by factor
-s scale by size, i.e. width and height
-k keep aspect ratio, use w for width and calculate the height
e.g. java PhotoScaler c:\temp\photos -f 0.5
     java PhotoScaler /tmp/photos -s 800 600
     java PhotoScaler c:\temp\photos -k 800