% filename: getGrayCodeBitPlane.m
% author: Alan Brooks
% description: Given gray scale double matrix, M(width,height,fr),
%   this function returns the Gray coded bit plane, bit.
% version history:
%   08-Mar-2003 created
%               optimized of debug_disp is off

function [Mg] = getGrayCodeBitPlane(M,bit,fr,debug_disp)

if debug_disp
    % slow (all bits)
    msb = 8;
    lsb = 1;
else
    % speedy
    msb = min([bit+1 8]);
    lsb = bit;
end

w = length(M(1,:,1)); % width
h = length(M(:,1,1)); % height

%  useful: bitget, dec2bin, num2bin, bitxor
M1bit = zeros(h,w,8);
M1bitGray = zeros(size(M1bit));
for b = msb:-1:lsb
    % compute original bit-planes (1 is LSB, 8 is MSB)
    M1bit(:,:,b) = bitget(M(:,:,fr),b); % fr'th frame
    % compute gray coded bit-planes
    if b==8 % MSB
        M1bitGray(:,:,b) = M1bit(:,:,b);
    else % LSB's
        M1bitGray(:,:,b) = bitxor(M1bit(:,:,b),M1bit(:,:,b+1));
    end
end

% Single bit output value
Mg = M1bitGray(:,:,bit);

% Debugging displays
if debug_disp
    for b = 8:-1:1
        figure,imshow(M(:,:,fr),[0 255]) % orig
        figure,set(gcf,'name',sprintf('Bit-Plane for bit # %d',b))
        imshow(M1bit(:,:,b)) % normal
        figure,set(gcf,'name',sprintf('Gray Bit-Plane for bit # %d',b))
        imshow(M1bitGray(:,:,b)) % gray
    end
end

return