5 April 2009

Sony Ericsson Theme File Format

Recently I wanted to pimp my Sony Ericsson mobile and add some nice themes (.thm files). There were plenty of them around and I just downloaded a collection of some hundred free ones. Unfortunately most came without a preview image and going through these on my mobile to find nice ones was painstaking and slow: I had to activate each of them, return to the standby mode, check out the main image, return to the theme manager, and start over again. What I needed was some kind of theme browser. I did not trust the Sony Ericsson Themes Creator application to provide browsing and did not bother installing it.

Sony Ericsson G705 - Keypad As being a hard core developer I had a look into the THM files. I STFW but could not find any resources explaining the file format. So I explored it a bit myself. Here is what I found together with some Ruby code.

Sony Ericsson Theme File (.THM) Format
The file contains several files concatenated together with some kind of header before the data.
  • At 0x0000 a null-terminated string with the name of the original file. Remaining bytes are all null. This is read with name = data[ofs..ofs+0x63].strip.
  • At 0x0064 several null-or-blank-terminated strings containing octal numbers. The number fields may contain blanks which are treated as separators as well. Parse them with
    numbers = data[ofs+0x64..ofs+0x100].
    collect { |n| n.to_i(8) }
  • The only important number is the fourth (body_len = numbers[3]), which is the length of the data body in bytes. If this number is not positive then the file is corrupt.
  • At 0x0101 there is most of the time the string ustar and at 0x0129 nogroup, but we do not need them.
  • At 0x0200 starts the data: body = data[ofs+0x200...ofs+0x200+body_len].
  • After 0x0200+body_len the space is filled with nulls until the next address continuing a zero low-byte. We just skip them until data[ofs] != 0.
  • Repeat these steps until EOF.
Usually the first item in the theme file is called Theme.xml. This is an XML configuration file and looks something like
<Sony_Ericsson_theme version="4.5">
<Background Color="0xb5f8fd"/>
<Background_image Source="desktop.png"/>
<Desktop Color="0xb5f8fd"/>
Sometimes it's not called in this way, but any XML file will do. The Color looks like a regular HTML Colour Code. The Source is a reference to an image stored inside the theme file. The important image types are
  • Standby_image - main image.
  • Desktop_image - background in the menu.
  • Popup_image - background of popup.
  • There are a lot more, but often these three images are reused in smaller themes.
Knowing the standby image name, it is possible to extract it to the file-system (File.open(filename,'wb') {|io| io.write body}). Then browsing these preview images with some image utility and deleting unwanted ones is a piece of cake. The whole Ruby program is here. Have fun!


José said...

You know, the .thm files are actually plain old .tar files. You can open them with any decent decompression program (in Windows, I personally use IZArc)

Once open, you get that XML file you saw plus (possibly) a bunch of .png, .jpg .gif, or .swf files. It's really nothing special.

José said...

Oh, and btw... see if this link works for you: Themes Developer guide

Peter Kofler said...

Thanks José, knowing that it's a TAR would have saved me some work. (But know I know I reverse engineered tar format ;-) I'm wondering why the chose such an old file format...