Smoothed histogram of image
s.hist
A GAM from mgcv
for x and y from histograms
if (FALSE) {
data(t2.voi.hist)
y = t2.voi.hist$counts
x = t2.voi.hist$mids
x = x[!is.na(y)];
y = y[!is.na(y)]
# 70 used for speed of example
s.hist = smooth_hist(x, y, k=70)
}