calculate -3dB of given picture?

this code calculate HPBW of produce image with matlab( peaks order) clc; % Clear the command window. close all; % Close all figures (except those of imtool.) workspace; % Make sure the workspace panel is showing. fontSize = 20;

% Create sample data. H = peaks(90); H = 11*mat2gray(H) - 13; % Display it. subplot(2, 2, 1); surf(H); xlabel('Azimuth [deg]', 'FontSize', fontSize); ylabel('Elevation [deg]', 'FontSize', fontSize); % Enlarge figure to full screen. set(gcf, 'units','normalized','outerposition',[0 0 1 1]); % Maximize figure. set(gcf,'name','Demo by ImageAnalyst','numbertitle','off')

% Threshold the image binaryImage = H > -3; % Display it. subplot(2, 2, 2); imshow(binaryImage); axis on; xlabel('Azimuth [deg]', 'FontSize', fontSize); ylabel('Elevation [deg]', 'FontSize', fontSize);

measurements = regionprops(binaryImage, 'BoundingBox'); bb = [measurements.BoundingBox] x1 = bb(1); x2 = x1 + bb(3); y1 = bb(2); y2 = y1 + bb(4); % Plot box over image. hold on; plot([x1 x2 x2 x1 x1], [y1 y1 y2 y2 y1], 'r-', 'LineWidth', 2);

message = sprintf('The Azimuth Width at -3 dB = %.1f\nThe Elevation Width at -3 dB = %.1f', ... bb(3), bb(4)); msgbox(message);

how can i run it for my image that linked below?

http://kmu.site40.net/images/19d3c9e40467.jpg