## Copyright (C) 2020 Jens
## 
## This program is free software: you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation, either version 3 of the License, or
## (at your option) any later version.
## 
## This program is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
## GNU General Public License for more details.
## 
## You should have received a copy of the GNU General Public License
## along with this program.  If not, see
## <https://www.gnu.org/licenses/>.

## -*- texinfo -*- 
## @deftypefn {} {@var{retval} =} alpha_gen (@var{input1}, @var{input2})
##
## @seealso{}
## @end deftypefn

## Author: Jens <jens@orion>
## Created: 2020-10-07

function a = alpha_gen(N, slope)
s = (0:N-1)/(N-1);
a = to_param(s, 0, 1, 2, -slope, 0.5, 0.5);

color_bg = [0.1 0.3 0.9];
color_fg = [0.9 0.9 0.0];

mean_fg  = mean(color_fg)
norm_fg = norm(color_fg)
mean_bg  = mean(color_bg)
norm_bg = norm(color_bg)

w = N;
h = 8;

im_a = repmat(a, h, 1);


im_comp = to_im (color_fg, a, h) + to_im (color_bg, 1-a, h);
im_fg = to_ref(color_fg, size(im_comp));
im_bg = to_ref(color_bg, size(im_comp));

im_ac = (im_comp - im_bg)./(im_fg - im_bg);

close all;
figure;
imshow(im_a); title ("im_a")

figure;
imshow(im_ac); title ("im_ac")

figure;
imshow(im_comp); title ("im_comp")

figure;
im_filtered = im_comp - to_ref(color_bg, size(im_comp));
imshow(im_filtered);  title ("im_filtered")

strip = im_filtered(1,:,:);
strip_clamped = max(0, strip);
strip_clamped_norm = strip_clamped;
n = vecnorm(strip, 2, 3)/norm_fg;
figure;
plot (s, a, s, n); grid; legend("Ground truth", "Calculated")

endfunction

function im = to_im(color, a, h)
w = length(a);	
im = reshape([color(1)*ones(h,1)*a color(2)*ones(h,1)*a color(3)*ones(h,1)*a], h, w, 3);
 
endfunction

function r = to_ref(ref, d)
	r = repmat(reshape(ref,1, 1, 3), d(1), d(2));
endfunction