Using a raw video to rip hardsubs

[lindewell]

Hi, i want to rip harsubs from anime videos, most of the time you can find the raw of the video. So I head the idea to subtract the two videos so that it nullifies the background.

Here is the script I used:

# Change the following line to your source file; avoid spaces in file name
v1 = AviSource("[Ch-F]_Terra_e_-_Toward_The_Terra_08_[94911D39].avi",Audio=False)
v1=v1.Greyscale()
#v1=Crop(v1,0,324,0,-10)
v2 = AviSource("[S^M] TOWARD THE TERRA 08 RAW.avi",Audio=False)
v2=v2.Greyscale()
#v2=Crop(v2,0,324,0,-10)

return v1.subtract(v2)

And here is the result:

Input 1:
http://img504.imageshack.us/img504/930/clipboard04cp4.jpg

Input 2:
http://img504.imageshack.us/img504/2979/clipboard05ak0.jpg

Output:
http://img504.imageshack.us/img504/5056/clipboard03cl1.jpg

The background turns to grey but I still have problems with the subtitles because they are merged with the background.
Any idea how I could keepthe texts without having this problem?

I'm using subtract, I know there is also the Overlay filter but I'm a beginner, I need advices thanks.