To apply general convolution kernels, use the Convolve operator. You can specify up to a 9×9 kernel in the node’s parameters, or connect an image to use as a kernel.
Convolving images is a slow operation, so try to keep the the kernel image smaller than 50×50.
Image displacement maps
Use the Deform operator to move pixels based on a displacement map.
Waves and ripples
You can use slowly animated, smooth noise as the basis for concentric ripples. Use a cycling Ramp node with a range from 0 to 1 and an interpolation of “Ease in Ease Out” to create ripples (concentric ramp) or waves (rotated horizontal map).
Create a Deform node and use the noise to displace the image.
You should use floating point images for distortion maps whenever possible. Otherwise, quantization errors can cause unwanted noise in the image.