This is regarding Fax Image compression. Initially I had an Uncompressed TIFF file , I wrote a code to extract its tags and the Image data present in it. Once I extracted the image data I performed 1D modefied Huffman coding/ Run length coding on it to get the encoded compressed data which I have stored in a textfile.
Now I am trying to recreate a TIFF file by modifying the tags appropriately to store the encoded compressed data. I have writen a code to recreate the tiff file and when I open the tiff file with an appliction to view all the tags, I find that all the tags I have put are correctly being read. However, when I use an online tiff viewer I do not get the correct image. I am confident that my encoded data is correct according to the Huffman Runlength tables. Anyone has any idea why I am not able to view the same Image with my compressed tiff file?
Note : I have not used any C libraries such as libtiff, The tiff file is just created by opening a tiff file and writing specific values at different offsets based on the tiff file stucture.
Thank you.
The Original Uncompressed file
The 1D encoded compressed file
Related
I have a really large txt file (80MB) that contains about 700 png files and I want to find a way to extract them.
All I know is that png files start with ‰PNG characters and end with IEND®B`‚ if they open in a text editor and I believe if I find a way to store all strings between those characters in seperate files (including the start and end chars of course) I will achieve my goal.
But I have no idea how to do this considering the giant size of txt file. I tried Notepad++ to open the large file and it crashes due to its tremendous size.
I am reading .docx file in a buffer and writing it to a new file successfully. (Using fread and fwrite in C) However now I want to enhance the scope of this project for the purpose of encryption. For which I want to be able to manipulate the buffer, then write it in new file.
Now one question might be, what manipulation do I need?
It could be anything really, like I'd write character 's' in buffer's location 15. Like below, and then write this new buffer (having character 's' at location 15, but the rest of the buffer remains unchanged) in a new .docx file.
buffer[15] = 's';
When I did this, the file that was created was corrupt. Since I am not fully aware of the structure of .docx file, this byte number 15 could be some potential identifier, or header, or any important information of .docx file needed for creating a non-corrupt file.
However, the things I know about .docx internal structure are:
It consists of XML files, zipped together.
The content that is written in .docx file, (for e.g. I have a file named test.docx, and it contains "Hello, how are you?") then the contents "Hello, how are you?" are stored in XML files.
There is a .rels (not confirm) extension file, among those files that are zipped together, that tells MS word about where the content is stored in file, i.e. where to look for content.
Apart from these 3 points I don't know much about structure of .docx file. Now considering all this, I want to be able to extract the contents of .docx file, from the XML files zipped together, read it (in C) in a buffer, change the buffer as I need it, and create a new file, with the new content that is present in the buffer.
Can someone guide me through this?
Also kindly mention, if I need to provide code, or any other essential details. Thanks in advance.
EDIT
PURPOSE OF ALL THIS:
I want to do all this for encryption. As by encrypting a file (using AES) the whole file will become unreadable, corrupt and everything inside will be changed from its place. When I decrypt that file, the file is unable to open. My guess is, as AES decryption algo does not know how to parse the contents recovered from decrypting the encrypted file, in to a new .docx file, thus it is unable to place the contents/structure properly in its place.
I have tried it. Original docx file was of 14 KB, encrypted docx file was of 14 KB as well as the decrypted docx file. But when I try to open the decrypted file, it says file is corrupt. Also I tried to check it in HEX editor. Decrypted file has just 00 bytes after exactly 30 Bytes.
DOCX files are based on OPC and OOXML. OPC is based on Zip. OOXML is based on XML. Therefore, you can use Zip and XML tools to operate on DOCX files. Beyond this, you'll have to be more specific about what you wish to do in order to receive better guidance.
Poking characters into random index locations in an XML file is operating at the wrong level of abstraction.
How Application will detect file extension?
I knew that every file has header that contains all the information related to that file.
My question is how application will use that header to detect that file?
Every file in file system associated some metadata with it for example, if i changed audio file's extension from .mp3 to .txt and then I opened that file with VLC but still VLC is able to play that file.
I found out that every file has header section which contains all the information related to that file.
I want to know how can I access that header?
Just to give you some more details:
A file extension is basically a way to indicate the format of the data (for example, TIFF image files have a format specification).
This way an application can check if the file it handles is of the right format.
Some applications don't check (or accept wrong) file formats and just tries to use them as the format it needs. So for your .mp3 file, the data in this file is not changed when you simply change the extension to .txt.
When VLC reads the .txt byte by byte and interprets it as a .mp3 it can just extract the correct music data from that file.
Now some files include a header for extra validation of what kind of format the data inside the file is. For example a unicode text file (should) include a BOM to indicate how the data in the file needs to be handled. This way an application can check whether the header tag matches the expected header and so it knows for sure that your '.txt` file actually contains data in the 'mp3' format.
Now there are quite some applications to read those header tags, but they are often specific for each format. This TIFF Tag Viewer for example (I used it in the past to check the header tags from my TIFF files).
So or you could just open your file with some kind of hex viewer and then look at the format specifications what every bytes means, or you search Google for a header viewer for the format you want to see them.
I need to convert 24 bit RGB(888) image data to PNG or JPEG image (whichever possible). Need simpler approach to do this same like converting RGB888 to BMP without any compression. Would be great if it is something like adding PNG/JPEG headers to the RGB data with/without little modification. Ready to provide more details on request..
Thanks in advance..
Language/Platform : C/Linux
Use miniz - a.k.a single C source file Deflate/Inflate compression library with zlib-compatible API, ZIP archive reading/writing, PNG writing.
If you just need an image format then the easiest is probably ppm (or pgm for greyscale)
You just need to add a small ascii header to the uncompressed binary data and most image apps will read it.
P6 <-- magic value for binary data
# a comment if you want
640 480 <-- width x height
255 <-- max pixel value
.... binary data here .......
I was wondering if sending a file with a jpg extension through a socket_stream, this automatically makes the transformation of bytes to jpg ? or need to implement some algorithm to transform the lot of bytes to image... Please could somebody explain me the way to do?
JPEG images are nothing but a bunch of bytes organized according to the JPEG format. A network socket isn't going to organize random bytes into the JPEG format. You can send the bytes that make up a JPEG formatted image across a socket as a binary blob, receive it on the other end, and write it to a file with a .jpg extension. An application can interpret this file as a JPEG image based on the extension and try to display it. But you are still responsible for providing a set of bytes that are organized as a JPEG image.