[Insight-users] GradientImageFilter vs. GradientRecursiveGaussianImageFilter

[Michael]

Hi,

what exactly are the differences between the GradientImageFilter and the 
GradientRecursiveGaussianImageFilter (except of the way they calculate 
the gradient image)?

In both cases I would expect an output image that consists of pixels 
with values [derivative1, derivative2, ..., derivativeN]. This means in 
2D pixels with values [derivativeX, derivativeY], where derivativeX 
denotes the derivative in direction x at the pixel position and 
derivativeY the derivative in direction y. Say, we have a pixel at 
position [x0, y0]. Then derivativeX should evaluate to approximately

(GetPixel(x0 + delta, y0) - GetPixel(x0 - delta, y0)) / (2 * delta)

for both filters. Is this correct?

If yes, how do the filters perform (compared to each other) with respect 
to speed and memory consumption?

If no, what are the filters supposed to do?

Thanks,

Michael