MatlabProject/q3_2_3_decode.m at master · baron0426/MatlabProject · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
clear all;
close all;
clc;
load('q3_2_3_jpegcodes.mat');
load('JpegCoeff.mat','DCTAB','ACTAB');
blockCntRow = floor(height/8);
blockCntCol = floor(width/8);
blockCnt = blockCntRow*blockCntCol;
DC_decode = zeros(1, blockCnt);
last = 1;
max_sizecode_length = max(DCTAB(:,1));
code_length = length(DC_code);
m = 1;
while(last<=code_length)
    for k = 2:1:max_sizecode_length
        query = find(~any((~(DCTAB(:,2:1+k) == DC_code(last:last+k-1))), 2));
        if(length(query) == 1)
            sizee = query - 1;
            last = last+k;
            break;
        end
    end
    if(sizee ~= 0)
        last_next = last + sizee;
        if(DC_code(last))
            magnitude = bi2de(flip(DC_code(last:last_next-1)));
        else
            magnitude = -1 * bi2de(flip(~(DC_code(last:last_next-1))));
        end
        last = last_next;
    DC_decode(m) = magnitude;
    else
        DC_decode(m) = 0;
    end
    m = m +1;
end
DC_decode = filter(-1, [1,-1],DC_decode,2*DC_decode(1));
AC_decode = cell(1,blockCnt);
last = 1;
max_sizecode_length = max(ACTAB(:,3));
code_length = length(AC_code);
m = 1;
ind = 1;
AC_decode{m} = zeros(63,1);
while(last<=code_length)
    if(AC_code(last:last+3) == logical([1,0,1,0]))
        last = last+4;
        if(last <= code_length)
        	m = m + 1;
            ind = 1;
            AC_decode{m} = zeros(63,1);
        end
        continue;
    elseif(last+10<=code_length)
        if(AC_code(last:last+10) == logical([1,1,1,1,1,1,1,1,0,0,1]))
        AC_decode{m}(ind:ind+15) = zeros(16,1);
        ind = ind + 16;
        last = last+11;
        continue;
        end
    end
        for k = 2:1:max_sizecode_length
            query = find(~any((~(ACTAB(:,4:3+k) == AC_code(last:last+k-1))), 2));
            if(length(query) == 1)
                if(query == 4 || query == 62)
                    k = k + 1; %ZRL and EOB are not included in the ACTAB,
                               % which destroy the prefix encoding
                               % property! It is essential to add this
                               % conditioning!  HOW CAN YOU GIVE ME AN
                               % INCOMPLETE ACTAB WITHOUT MENTIONING IN THE
                               % INSTRUCTIONS?
                end
                run = ACTAB(query,1);
                sizee = ACTAB(query,2);
                last = last+k;
                break;
            end
        end
         AC_decode{m}(ind:ind+run-1) = zeros(run,1);
         ind = ind + run;
         last_next = last + sizee;
         if(AC_code(last))
            magnitude = bi2de(flip(AC_code(last:last_next-1)));
         else
            magnitude = -1 * bi2de(flip(~(AC_code(last:last_next-1))));
         end
         last = last_next;
         AC_decode{m}(ind) = magnitude;
         ind = ind + 1;

end
AC_decode = cell2mat(AC_decode);
decode_result = [DC_decode; AC_decode];
clear last;
clear last_next;
clear ind;
clear m;
clear k;
clear magnitude;
clear run;
clear sizee;
clear max_sizecode_length;
clear query;
clear DCTAB;
clear ACTAB;
[decode_result_rowCnt,~] = size(decode_result);
decode_pic = cellfun(@IZigzagScanandIDCT8,mat2cell(decode_result,decode_result_rowCnt ,ones(1,blockCnt)),'UniformOutput', false);
decode_pic = cell2mat(reshape(decode_pic, blockCntCol, blockCntRow)');
% %extract hide message
recovered_msg_ind = cellfun(@q3_2_3_findInd,mat2cell(decode_result,decode_result_rowCnt ,ones(1,blockCnt)));
recovered_msg = decode_result(sub2ind(size(decode_result), recovered_msg_ind, 1:1:blockCnt));
recovered_msg(recovered_msg == -1) = 0;
recovered_msg = logical(recovered_msg);
recovered_msg(length(recovered_msg) - mod(length(recovered_msg),7)+1 : length(recovered_msg)) = [];
recovered_msg = reshape(recovered_msg, 7,[])';
recovered_msg = bi2de(recovered_msg, 'left-msb');
recovered_msg(recovered_msg == 0) = [];
recovered_msg = char(recovered_msg)';
disp(recovered_msg);


load 'hall.mat';
subplot(1,2,1);
imshow(hall_gray,'InitialMagnification','fit');
title('Original');
subplot(1,2,2);
imshow(uint8(decode_pic),'InitialMagnification','fit');
title('JPEG with hidden message');
temp = (decode_pic - double(hall_gray)).^2;
MSE = 1/(height*width)*sum(temp(:));
PSNR = 10*log10(255^2/MSE);