Convert color image into 256 greys ( 8 bpp)

[mirtoni]

ok, I hope that someone here can help me with this problem.

I have a school project the details of which I would not like to go
into but i involves text from pictures that need to be in 256 greys
format.

I am using JAI to acomplish this but the results are not very good.

Below is the source code of the class that handles the conversion
process:

http://www.pjwstk.edu.pl/~s3288/ColorModelConverter.java

And this is the color image that I want to convert:

http://www.pjwstk.edu.pl/~s3288/test(color).jpg

The result from the conversion:

http://www.pjwstk.edu.pl/~s3288/test(dark grey).jpg

And this is the kind of reult that I would like to achive:
(which in fact was done with ACDSee ver 6.0)

http://www.pjwstk.edu.pl/~s3288/test(grey).jpg

I know I know there is probably one parameter of brightnes or something
that needs to be adjusted but Im not a professional programer and JAI
is kinda unnecessarily complicated.

Any help/advice will be appriciated

Thank you.