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Explanation for LSB data hiding

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Elysi Cochin
Elysi Cochin 2017-3-23
回答： dbmn 2017-3-23
Please can someone explain what does the numbers 248, 252, 128, 64 denote, in
red = bitand(redc,248);
blue = bitand(bluec,252);
bitand(text,128) == 128
bitand(text,64) == 64
bitor(red,4)
bitor(red,2)
bitor(red,1)
The below is a few lines from LSB...
red = bitand(redc,248);
green = bitand(greenc,248);
blue = bitand(bluec,252);
if bitand(text,128) == 128
red = bitor(red,4);
end
if bitand(text,64) == 64
red = bitor(red,2);
end
if bitand(text,32) == 32
red = bitor(red,1);
end

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采纳的回答

dbmn
dbmn 2017-3-23
you might get an answer if you leave the decimal notation and go to binary. Here is a mini example
dec2bin(248) = 11111000
dec2bin(252) = 11111100
So bitand(redc, 248) gets you all but the last 3 digits of your redc.
dec2bin(bitand(bin2dec('10101011'), 248)) = 10101000
I assume that you store whatever Info you need in that 3 digits. Similarly bitand(redc, 7) will get you the last 3 bits with the desired info.
dec2bin(bitand(bin2dec('10101011'), 7)) = 00000011
You might play around with bitand and bitor for clarity.

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