www.pudn.com > SPIHT_bandelet.rar > load_image_small_square.m

function M = load_image_small_square(name, p, options) 
 
% load_image_small_square - extract a sub-square from an image. 
% 
%   M = load_image_small_square(name, p, options); 
% 
%   p is the size of the small square. 
%   name is the name of the undelying image, please see 'help load_image' 
%   options can override default features. 
% 
%   Copyright (c) 2005 Gabriel Peyré 
 
options.null = 0; 
 
if isfield(options, 'use_wavelets') 
    use_wavelets = options.use_wavelets; 
else 
    use_wavelets = 1; 
end 
 
if isfield(options, 'use_filtering') 
    use_filtering = options.use_filtering; 
else 
    use_filtering = 0; 
end 
 
if isfield(options, 'wavelet_scale') 
    wavelet_scale = options.wavelet_scale; 
else 
    wavelet_scale = 0; 
end 
 
if isfield(options, 'n') 
    n = options.n; 
else 
    n = 256; 
end 
 
% set up the ROI for extraction 
c = [0.5,0.5];        % default roi center 
switch lower(name) 
    case 'lena' 
        c = [0.8022, 0.6767]; 
    case 'lena_bis' 
        c = [0.875,0.665]; 
    case 'quarterdisk' 
        c = [0.38,0.72]; 
    case 'real_wall_1024' 
        c = [0.51,0.57]; 
    case 'peppers' 
        c = [0.821,0.306]; 
    case 'peppers_line' 
        c = [0.821,0.306];     % line 
    case 'peppers_curve' 
        c = [0.21,0.136];      % curve 
    case 'barb' 
        c = [0.478,0.62]; 
    case 'barb_left_pant' 
        c = [0.662,0.388];     % left pant 
    case 'real_light' 
        c = [0.59,0.32];         
    case 'line' 
        options.theta = 1/sqrt(2); 
        options.eta = 0.5-options.theta*0.5; 
end 
 
% load the original image 
M = load_image(name, n, options); 
 
% perform a 2D wavelet transform 
if use_wavelets 
    Jmin = 1; 
    Jmax = log2(n)-1; 
    j = Jmax - wavelet_scale; 
    q = 1; 
    % use 7-9 wavelet transform 
    options.wavelet_vm = 4; 
    MW = perform_wavelet_transform(M,Jmin,1,options); 
    % select sub-square 
    [selx,sely] = compute_quadrant_selection(j,q);  
    MW = MW(selx,sely); 
elseif use_filtering>0 
    sigma = use_filtering; 
    MW = conv2(M, ones(sigma)/sigma^2, 'same');     
else 
    MW = M; 
end 
 
% crop sub-image 
n = length(MW); 
cn = floor(c*(n-1))+1; 
p1 = floor(p/2); p2 = ceil(p/2); 
M = MW( cn(1)-p1+1:cn(1)+p2, cn(2)-p1+1:cn(2)+p2 );