That's right, you have to use TLazInfImage instead. You can keep using TBitmap, but when you need the Scanline, just create a copy in a TLazInfImage and work on it... I don't understand why they made it that way, but I use it in my own engine and works fine. You can see more about that in:

http://wiki.lazarus.freepascal.org/D...th_Graphics/es
http://www.lazarus.freepascal.org/lc...IntfImage.html

Saludos!!