Set bitmap as wallpaper

Set bitmap as wallpaper

Well my bitmap have the exact size of the device screen, so for this
example lets say 1200x780. If I set that bitmap as the wallpaper with this
code:
WallpaperManager myWallpaperManager =
WallpaperManager.getInstance(getApplicationContext());
myWallpaperManager.setBitmap(bitmap);
My wallpaper gets zoomed and the image look horrible. So my question is:
If the bitmap is the exact same size as the device screen, how could I set
it as wallpaper without it get zoomed?