demo_bilatfilt_gradient.m

%% A demo of a bug in bilateral3()
% Demonstrates two separate issues

%% The test image - a simple gradient
im1 = repmat(uint8(1:30),[30 1 30]);

% visualize it:
imshow(im1(:,:,1),[],'InitialMagnification',1000);


%% Apply smoothing 
% using extremely small spatial sigma (degenerate, zero-smoothing case) causes issues:
sigmaSxy = 0.1;
sigmaSz = 0.1;
sigmaR = 1;
samS = 5;
samR = 5;
verbose = false;
im2 = bilateral3(im1, sigmaSxy,sigmaSz,sigmaR,samS,samR,verbose);   


%% Issue1: scaled colors
% Although `im1` values are in [1, 30], `im2` values are scaled to [0, 255]. 
assert(abs(max(im2(:))-255)<1e-10);

disp('max(im2(:)) :')
disp(max(im2(:)));

disp('min(im2(:)) :')
disp(min(im2(:)));

%% Issue2: The result is non-monotonous:
% It is natural to expect that smoothed version of a monothonous gradient
% would be monothonous in any case, but the result we have is not monothonous:

% visualize it:
imshow(im2(:,:,1),[],'InitialMagnification',1000);

%% Testing the one-line quick-and-dirty fix for issue2:
% (see details inside "bilateral3_fixed.m")
im3 = bilateral3_fixed(im1, sigmaSxy,sigmaSz,sigmaR,samS,samR,verbose);  
        
% visualize it:
imshow(im3(:,:,1),[],'InitialMagnification',1000);