BMP to GJEP conversion

From: Mina Doroudi (dormina_at_helsinki.cc.gatech.edu)
Date: 04/23/05

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    Date: 23 Apr 2005 21:19:42 GMT

    I am woring on a steganography project, and I was trying to
    figure out how BMP -> JPEG conversion works, I read some
    explanation about it, and from my understanding the conmversion
    tool takes each 8x8 pixel of BMP and converts it to a pixel in
    JPEG, and respectively gives it a proper color. so there is no
    distinction btw which bits are better to be converted...
    Am I correct?

    So, in one tupe of steganography (LSP method) it takes the binary
    representation of the data, and overwrite the least significant of
    each byte with a bit of message.

    In the articles that I read, they said the compressed file is better because:

    1. the information in the compressed file has already run through an entropy encoder
       whose job was to compress out useless information, therefore it is hard to find
       those least significant bit for hiding data!
            -> I dont' see why is this hard, so the least significant bit is for each byte
               there is a LSB, so it doesn't matter if the file is compressed or not!
               what am I not getting in here??? when it compresses a file does it care
               whic bits are useless?? it doesn't seem like it, from what I read.
    2. the compressed are imune against visual attack, which is when you filter the
       non-significant bits, and only look at the significants too see if they are changed.
            -> why does it make a difference, when you filter it since you only see the
               replacement bits, it doesn't matter what they are replacing...

    I apreciate any kind of help!

    Mina 

    -- 
					
			-Mina Doroudi (dormina@cc.gatech.edu)
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