cbir_edgedirection.m

matlab编程

function edgehist = CBIR_edgedirection(rgb)
% EE6850 HW3, Content-Based Image Retrieval
% CBIR_edgedirection() -- edge direction histogram calculation
% input:
%   MxNx3 image data, in RGB
%   or MxN luminance channel only
% output:
%   1x5 edgehistogram <== global 5 bins (0, 45, 90, 135, no-oreintation)
% NOT the MPEG-7 edge histogram descriptor:
% 
% 10-25-2001, [e-mail]

DEBUG = 0;
if DEBUG
    subplot(231);
    imshow(rgb); title('original');
end
% check input
if length(size(rgb)) == 2
    % take as luminance directly
    lum = rgb;
elseif size(rgb,3) == 3
    % convert to luminance
    lum = rgb2ycbcr(rgb);
    lum = lum(:,:,1);
end
imgsize = size(lum);
% get rid of irrelevant boundaries
i0=round(0.05*imgsize(1));  i1=round(0.95*imgsize(1));
j0=round(0.05*imgsize(2));  j1=round(0.95*imgsize(2));
lum = lum(i0:i1, j0:j1);
imgsize = size(lum);
if DEBUG
    subplot(232);
    imshow(lum); title('central portion lum.');
end

sobel_y = [1 0 -1; 2 0 -2; 1 0 -1];
sobel_x = [1 2 1; 0 0 0; -1 -2 -1];
g_x = filter2(sobel_x, lum, 'same');
g_x = g_x + (g_x==0)*1e-6;  % for numeric stability
g_y = filter2(sobel_y, lum, 'same');
tg = g_y./g_x;

edgemap = edge(lum, 'sobel');
% threshhold for edge direction quantization: 
% upperbound; lowerbound (the last one is for absolute value)
TH = [ tan(pi/8), tan(pi*3/8), tan(-pi/8), Inf; ...
        tan(-pi/8), tan(pi/8), tan(-pi*3/8), tan(pi*3/8)];
edgedir = [0 45 -45 90];
for i = 1:4
    if i~=4
        directmap = (tg<TH(1,i) & tg>=TH(2,i));
    else
        directmap = ((abs(tg)<TH(1,i)) & (abs(tg)>=TH(2,i)));
    end
    edgehist(i) = sum(sum(directmap & edgemap));
    if DEBUG
        subplot(2,3,i+2);
        imshow(directmap & edgemap);
        title([num2str(edgedir(i)) '^o edge #: ' num2str(edgehist(i))]);
    end
end

edgehist = edgehist/prod(imgsize);
%sum(edgehist)