im_lowpass - remove high frequencies quickly
int im_lowpass(in, out, x, y)
IMAGE *in, *out;
int x, y;
Expand image up to X by Y pixels. Linear interpolation. Used by
lowpass(1X) for simple and nasty low-pass filtering. The result is very
poor, but good enough for smoothing out whites. Any number of bands,
output size == input size, any non-complex type.
The function returns 0 on success and -1 on error.
Too embarrassed to say
2 May 1991 IM_CONV(3)