 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
.NET Forum / Languages / C# / February 2008Modify Jpeg via BinaryWriter renders "useless" output
Hello, If i take a jpeg and pipe it from a binary reader to a binary writer, everything is fine and I can still use it. If i take that same jpeg and piping code and simply add a byte encoded string to the front of the file then I can no longer open it in an image editor. This i would expect. However if i open that image in notebook and remove the string I entered, then i still cant open the file in an image editor, does anyone know why this is?? Once ive removed the 4 character string with notepad the files are "seemingly" exactly the same?? They have precisely the same file size (down to the byte) and the bytes within the file are also exactly the same?? Whats different? Thanks > If i take a jpeg and pipe it from a binary reader to a binary writer, > everything is fine and I can still use it. [quoted text clipped - 9 lines] > > Whats different? That's almost certainly due to using notepad rather than anything the .NET code is doing. When anything tries to interpret arbitrary binary data as text it's very easy to lose information. Take the .NET code out of the equation by doing the same steps manually with your text editor and you're likely to see the exact same behaviour. If you don't, we'd need to see the actual code involved.  SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet World class .NET training in the UK: http://iterativetraining.co.uk Hi there, You're right. But if i do a byte by byte comaprision the files (the original vrs the modified after i use notepad to take out the test string and then save the file) they are still the same? So if i was removing or altering something other than the 4 byte test string surely the file contents would be different. Is this something to do with the os file system itself?? Other than partition types etc, I didn't realise the file system actually "defined" the file. I thought the whole idea of the file was that it encapsulated its own meaning?? Thanks >> If i take a jpeg and pipe it from a binary reader to a binary writer, >> everything is fine and I can still use it. [quoted text clipped - 19 lines] > with your text editor and you're likely to see the exact same > behaviour. If you don't, we'd need to see the actual code involved. > You're right. > > But if i do a byte by byte comaprision the files (the original vrs the > modified after i use notepad to take out the test string and then save the > file) they are still the same? How are you doing the comparison? > So if i was removing or altering something other than the 4 byte test string > surely the file contents would be different. Yes, and I suspect you'll find they *are* different. > Is this something to do with the os file system itself?? Other than > partition types etc, I didn't realise the file system actually "defined" the > file. I thought the whole idea of the file was that it encapsulated its own > meaning?? No, I suspect it's more likely to be to do with opening the file in Notepad, and the way you're comparing the two files. If you've got two files with the same contents and file A opens up fine as a JPEG, then I would expect file B to open fine likewise. SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet World class .NET training in the UK: http://iterativetraining.co.uk Hi there, Im using a couple of binary reader to loop through each byte in each file in sequential order and doing a compare on each byte.... although i suspect a simple hash would work just as well. Reversing the process as per Hans suggestion gives me back a useable Jpeg which in turn supports your idea that its notepad... which makes sense.... but i cant find the "difference" between the two files. Thanks >> You're right. >> [quoted text clipped - 23 lines] > If you've got two files with the same contents and file A opens up fine > as a JPEG, then I would expect file B to open fine likewise. > Im using a couple of binary reader to loop through each byte in each file in > sequential order and doing a compare on each byte.... although i suspect a [quoted text clipped - 3 lines] > which in turn supports your idea that its notepad... which makes sense.... > but i cant find the "difference" between the two files. That suggests that your comparison code is broken. Could you post it? SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet World class .NET training in the UK: http://iterativetraining.co.uk > Hi there, > [quoted text clipped - 7 lines] > > Thanks <snip replies from Jon> Try using the command line file comparison tool built into Windows: fc /B a.jpg b.jpg The /B is just to make sure you're using a binary comparison, since I do not know the heuristics involved in determining if the files are text. SignatureLasse Vågsæther Karlsen mailto:lasse@vkarlsen.no http://presentationmode.blogspot.com/ PGP KeyID: 0xBCDEA2E3 If your goal is to embed messages into images, you want to look into steganography. Corinna Johns has a series of articles on codeproject.com on the subject. -- Peter Site: http://www.eggheadcafe.com UnBlog: htp://petesbloggerama.blogspot.com Short Urls & more: http://ittyurl.net > Hello, > [quoted text clipped - 13 lines] > > Thanks Hi Peter, no it wasn't but thanks for the response, ive always wonderd what that was called. Spies and school kids use that stuff right? > If your goal is to embed messages into images, you want to look into > steganography. Corinna Johns has a series of articles on codeproject.com [quoted text clipped - 24 lines] >> >> Thanks Richard Coltrane formulated on zondag : > Hello, > [quoted text clipped - 13 lines] > > Thanks Try using your own process in reverse: use a .Net program to strip those first bytes and leave the rest of the data intact. I suspect that that *will* work (see the other replies) Hans Kesting Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
|
Reply to this Message
|
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2008 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.