function result = jpgandalpha( test, msg)
quality = 10:10:100; 
alpha = 0.1:0.1:1; 
result = zeros( [ max( size( alpha) ) max( size( quality) ) ] ) ;
resultr = 0; 
resultc = 0;
for a = alpha 
    resultr = resultr + 1;
    [ count, message, hideresult] = hidedctadv( test, 'temp.jpg', msg, 2003, a) ; 
    resultc = 0;
    different = 0; 
    for q = quality
        resultc = resultc + 1; 
        imwrite( hideresult, 'temp.jpg', 'jpg', 'quality', q) ;
        msgextract = extractdctadv( 'temp.jpg', 'temp.txt', 2003 , count) ; 
        for i = 1: count
            if message( i, 1) ~= msgextract( i, 1) 
                different = different + 1; 
            end
        end
        result( resultr, resultc) = different / count; 
        different = 0;
    end
    disp( [ '完 成 了 第', int2str(resultr) , '个 ( 共 10 个) α 的 鲁 棒 性 测 试, 请 等 待. . . '] ) ; 
end
% return
for i = 1:10 
    plot( quality, result( i,:) ) ; 
    hold on;
end
xlabel( 'jpeg 压缩率') ; 
ylabel( '提取的信息与原始信息不同的百分比例') ; 
title( '控制阈值 α在 JPEG 条件下对隐藏鲁棒性的影响')