geq=equation
generic equation change filter
<equation>
Some equation, e.g. 'p(W-XY)' to flip the image hori-
zontally. You can use whitespace to make the equation
more readable. There are a couple of constants that can
be used in the equation:
PI: the number pi
E: the number e
X / Y: the coordinates of the current sample
W / H: width and height of the image
SW / SH: width/height scale depending on the current-
ly filtered plane, e.g. 1,1 and 0.5,0.5 for YUV
4:2:0.
p(x,y): returns the value of the pixel at location
x/y of the current plane.
