annotate general/discretise/linmap.m @ 61:eff6bddf82e3 tip

Finally implemented perceptual brightness thing.

function M=linmap(p1,p2,p3)
% linmap - Create linearly spaced discretisation map
%
% linmap :: Min:real, Max:real, N:natural -> dmap(N).
% linmap :: [Min,Max]:[[1,2]], N:natural -> dmap(N).
%
% Parameters work almost but not quite like linspace: the
% third parameter is the number of GAPS, not the number of
% points, defining the map, So for a map with edges at 0:10,
% use linmap(0,10,10). To get the same edges from linspace,
% you would need linspace(0,10,11).

% unpack parameters
if nargin==2, min=p1(1); max=p1(2); bins=p2;
else min=p1; max=p2; bins=p3; end

dx=(max-min)/bins;
M=dmap(bins,@(t)map(bins,min,1/dx,t),@(t)revmap(min,dx,t));

function I=map(N,min,k,X)
	I=1+floor(k*(X-min));
	I(I<1)=-inf;
	I(I>N)=inf;

function X=revmap(min,ik,I)
	I=shiftdim(shiftdim(I),-1);
	X1=min+(I-1)*ik;
	X2=min+(I)*ik;
	X=cat(1,X1,X2);