Distortion problem

[ziasumo]

It took two days but problem is still here.I want to distort an image with white background..
But when I try to distort image
convert mandril.jpg -distort Perspective "0,0,0,0 0,128,0,128 128,128,128,108 128,0,128,20" output.jpg
input image

Output image

But I dont want to that upper and left area(excluded from distoted area) should background white...or transparent dont want to draw border before..

Eagerly waiting for magic reply..

[fmw42]

see viewtopic.php?f=3&t=15756