it seems to be offset because if i modify this
snapShot.ReadPixels( new Rect( camera.pixelRect.xMin, camera.pixelRect.xMin-40, (int)camera.pixelWidth, (int)camera.pixelHeight), 0, 0, false );
that 40 modify the Y offset but depends on the resolution. I cant know which calculation i have to do to have the exactly point and size