Image sampling matlab

To perform sampling of an image in matlab

 

 

Program:

%% matlab coding for image sampling

 

if (nargin==0)

    hFig    = figure( 'visible','off' );

    hImage  = image;

    Child   = get( hImage,'cdata' );

    close( hFig );

            out     = updownsample( Child,300,300,0,1 );

            figure;

            colormap gray;

            subplot( 1,2,1 );

            imagesc( Child );

            subplot( 1,2,2 );

            imagesc( out );

    return

elseif (nargin<5)

    error( 'UpDownSample - insufficient input parameters' );

end

% get input image size, and calculate the gain

[in_y_sz,in_x_sz] = size( in_m );

gain_x = out_x_sz/in_x_sz;

gain_y = out_y_sz/in_y_sz;

% check if up/down sampling is needed at all

if (gain_x == 1) & (gain_y==1)

    % same gain -> do not change sampling rate

    if is_fourier_flag

        switch is_real_flag

            case 0, out_m = ifft2( in_m );

            case 1, out_m = real( ifft2( in_m ) );

            case 2, out_m = abs( ifft2( in_m ) );

        end

    else

        out_m = in_m;

    end

else

    % upsample or downsample as needed

    % convert to fourier domain, if input is given in the space domain

    if ~is_fourier_flag

        in_m = fft2(in_m);

    end

      % if the input is even & output is odd-> use floor for all

    % if the output is even & input is odd -> use ceil for all

    % for downsampling -> the opposite

    if (~mod( in_x_sz,2 ) & (out_x_sz>in_x_sz)) | (mod( in_x_sz,2 ) & (out_x_sz<in_x_sz))

        x_output_space  = max(floor((out_x_sz-in_x_sz)/2),0) + [1:min(in_x_sz,out_x_sz)];

        x_input_space   = max(floor((in_x_sz-out_x_sz)/2),0) + [1:min(in_x_sz,out_x_sz)];

    else

        x_output_space  = max(ceil((out_x_sz-in_x_sz)/2),0) + [1:min(in_x_sz,out_x_sz)];

        x_input_space   = max(ceil((in_x_sz-out_x_sz)/2),0) + [1:min(in_x_sz,out_x_sz)];

    end

    if (~mod( in_y_sz,2 ) & (out_y_sz>in_y_sz)) | (mod( in_y_sz,2 ) & (out_y_sz<in_y_sz))

       y_output_space  = max(floor((out_y_sz-in_y_sz)/2),0) + [1:min(in_y_sz,out_y_sz)];

       y_input_space   = max(floor((in_y_sz-out_y_sz)/2),0) + [1:min(in_y_sz,out_y_sz)];

   else

       y_output_space  = max(ceil((out_y_sz-in_y_sz)/2),0) + [1:min(in_y_sz,out_y_sz)];

       y_input_space   = max(ceil((in_y_sz-out_y_sz)/2),0) + [1:min(in_y_sz,out_y_sz)];

   end

       % perform the up/down sampling

    padded_out_m    = zeros( out_y_sz,out_x_sz );

    in_m            = fftshift(in_m);

    padded_out_m( y_output_space,x_output_space ) = in_m(y_input_space,x_input_space);

    out_m           = (gain_x*gain_y)*ifft2(ifftshift(padded_out_m));  

          switch is_real_flag

        case 0, % do nothing

        case 1, out_m   = real( out_m );

        case 2, out_m   = abs( out_m );

    end

   

end