load roses
imagesc(xrose)
imagesc(xfrisbee)
xf = 2*double(xfrisbee)/255 - 1; xf = sum(xf,3);
xr = 2*double(xrose)/255 -1;     xr = sum(xr,3);
imagesc(xf); colormap gray
imagesc(xr); colormap gray

w = xr(:) / norm(xr(:));
w' * xr(:)
w' * xf(:)
thr = (w' * xr(:) + w' * xf(:))/2

x=xr+1*randn(size(xr)); imagesc(x);
(w' * x(:)) - thr

x=xf+1*randn(size(xr)); imagesc(x);
(w' * x(:)) - thr