Hi l have a problem

The best you can do as far as removing excess transparency is stripping off edge rows or columns of pixels that each pixel within it is transparent. Once a row or column of pixels contains a non-transparent pixel, you cannot remove it without removing part of the actual image. The image will end up a rectangular image with at least one pixel along each of its four edges being non-transparent. I would think that you could cut and paste the smallest rectangular area of the image possible using paint.net. Correction: the 'isTouching' method is from the Actor class, not the Greenfoot class.

The greenfoot framework comes with multiple classes -- Greenfoot, GreenfootImage, GreenfootSound, World, Actor, MouseInfo and UserInfo. The are all made available to any class created within greenfoot that has the following import statement: I hope you can see why I made the correction above.