Is there a way to add JPEG comments ("COM" markers) to an existing JPEG image file using libjpeg?
It is certainly possible to do so by first decompressing an existing image to an in-memory buffer and then compressing the raw image again with jpeg_write_marker( ... JPEG_COM ... ) to add comments, and saving to disk. Unless there is a need to decompress first, doing this seems to be an overkill.
There's a tool called wrjpgcom, it's part of libjpeg. I think it does what you want. Perhaps you could look through its source to find out how it's done.
You can use jpeg_write_marker() during the writing of the output file to write the comment after setting it up. Then, use jpeg_read_coefficients() and jpeg_write_coefficients() (in place of the ordinary jpeg_read_scanlines() and jpeg_write_scanlines()) to read and write the raw, compressed data without actually decompressing and recompressing it.
See the section "Really raw data: DCT coefficients" in the libjpeg documentation. Be sure to read all the caveats mentioned there.
Someone may use JPEG Comment Editor created by Mwisoft. It automate adding / editing JPEG comments using Windows, instead of right-click JPEG file and click properties to manually add comments.
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I want to uncompress a gz file (e.g. "MyFile.gz") and saving its content in a specified path using zlib in C++.
In other words, if the path is "C:\StoredData\", I would like to write a C++ function that creates the file "C:\StoredData\MyFile"
How can I write it?
I do not understand what is the problem here.
Once the data is uncompressed, you can write it anywhere you want using the File Stream.
If you are facing any issues, you can edit your post.
Sorry to post as answer, as i can't add comments.
Read the documentation in zlib.h. The gz* functions will do what you want on the uncompression side. Then you just write the uncompressed data wherever you like.
I'm trying to write a JPEG file.
After I acquire the raw image and processing it by DCT, quantization and huffman coding, I would like to save it in the correct format. I couldn't find any libraries that help me to write proper header file, insert the two tables that I used (huffman and quantization), so I started writing everything by myself.
I started with the SOI marker, frame header and so on, but when I try to open the JPEG image with a viewer, it shows nothing, even in the properties. There's no information shown (e.g. the image dimension), even if I insert this info like written in the official documentation.
How can I write a proper JPEG header?
P.S
I use C++ and Visual Studio 2010.
Simple answer - it's complicated.
I would start with libjpeg and use it to just give you the approriate header. You can also use it as a reference for what the internal header structs look like
I have a JPEG file on disk which is not quite normal - this JPEG file has additional rubbish data appended behind End Of Image (FFD9). This JPEG file can still be opened by JPEG viewers though.
I wish to remove those additional information behind End Of Image (FFD9). The constraints are:
Must be done programatically
Must be lossless
Must use native code, e.g. C++
One way I've found out is to re-save the file using IrfanView command-line tool, using lossless JPG_TRANSFORM's command: /jpg_rotate. The additional data behind are automatically stripped off.
However, is there another way in which I can do it in C++ code, If possible, I do not wish to use exes like IrfanView to do it. I wish to do everything in code to keep things lean.
I am thinking of detecting the End Of File (FFD9), then save the buffer before EOF into another JPEG. But, how can I save the buffer losslessly?
I guess this is a file handling question and NOT an Image Processing related.
All you need to do write all data till EOF in your Image file into the resultant Image file.
Greetings all,
I am currently a rising Sophomore (CS major), and this summer, I'm trying to teach myself C++ (my school codes mainly in Java).
I have read many guides on C++ and gotten to the part with ofstream, saving and editing .txt files.
Now, I am interested in simply importing an image (jpeg, bitmap, not really important) and renaming the aforementioned image.
I have googled, asked around but to no avail.
Is this process possible without the download of external libraries (I dled CImg)?
Any hints or tips on how to expedite my goal would be much appreciated
Renaming an image is typically about the same as renaming any other file.
If you want to do more than that, you can also change the data in the Title field of the IPTC metadata. This does not require JPEG decoding, or anything like that -- you need to know the file format well enough to be able to find the IPTC metadata, and study the IPTC format well enough to find the Title field, but that's about all. Exactly how you'll get to the IPTC metadata will vary -- navigating a TIFF (for one example) takes a fair amount of code all by itself.
When you say "renaming the aforementioned image," do you mean changing metadata in the image file, or just changing the file name? If you are referring to metadata, then you need to either understand the file format or use a library that understands the file format. It's going to be different for each type of image file. If you basically just want to copy a file, you can either stream the contents from one file stream to another, or use a file system API.
std::ifstream infs("input.txt", std::ios::binary);
std::ofstream outfs("output.txt", std::ios::binary);
outfs << insfs.rdbuf();
An example of a file system API is CopyFile on Win32.
It's possible without libraries - you just need the image specs and 'C', the question is why?
Targa or bmp are probably the easiest, it's just a header and the image data as a binary block of values.
Gif, jpeg and png are more complex - the data is compressed
I want to decode JPEG files and obtain uncompressed decoded output in BMP/RGB format.I am using GNU/Linux, and C/C++.
I had a look at libjpeg, but there seemed not to be any good documentation available.
So my questions are:
Where is documentation on libjpeg?
Can you suggest other C-based jpeg-decompression libraries?
The documentation for libjpeg comes with the source-code. Since you haven't found it yet:
Download the source-code archive and open the file libjpeg.doc. It's a plain ASCII file, not a word document, so better open it in notepad or another ASCII editor.
There are some other .doc files as well. Most of them aren't that interesting though.
Unfortunately I cannot recommend any other library besides libjpeg. I tried a couple of alternatives, but Libjpeg always won. Is pretty easy to work with once you have the basics done. Also it's the most complete and most stable jpeg library out there.
MagickWand is the C API for ImageMagick:
http://imagemagick.org/script/magick-wand.php
I have not used it, but the documentation looks quite extensive.
You should check out Qt's QImage. It has a pretty easy interface that makes this task really easy. Setup is pretty simple for every platform.
If Qt is overkill, you can try Magick++ http://www.imagemagick.org/Magick++/. It supports similar operations and is also well suited for that sort of task. The last time I used it, I struggled a bit with dependencies for it on Windows, but don't recall much trouble on Linux.
For Magick++'s Image class, the function you probably want is getConstPixels.
I have code that you can copy ( or just use as a reference ) for loading a jpeg image using the libjpeg library.
You can browse the code here: http://code.google.com/p/kgui/source/browse/trunk/kguiimage.cpp
Just look for the function LoadJPGImage.
The code is setup to handle c++ binding of my DataHandle class to it for loading the image, that way the image can be a file or data already in memory or whatever.
A slightly out of the box solution is to acquire a copy of the netpbm tools, which transform images from pretty much any format to any other format via one of several very simple intermediate formats. They work well from the shell, and are most often used in pipes to read some arbitrary image, perform an operation on it, and write it out to some other format.
The pbm formats can be as simple as a plain ASCII header followed by the RGB data in ASCII or binary. They are intended to be simple enough to use without required a library to implement.
JPEG is supported in netpbm by read and write filters that are implemented on top of libjpeg.