C++ - How could I do some operation on bmp file? - c++

I am interesting to do some transformation, like change one color to another, count all used colors, and resize image. I DO NOT want to use any exist library, I would like write myslelf all code.
Summing up: How could I open BMP file and change it?

Start by learning the bitmap file format. It is very easy to understand and implement.
You can get any file format by going to www.wotsit.org and searching for the file type you want. In your case BMP. There are different types of bitmaps so you can figure out which ones you want to implement.

I would start with reading some documentation. Maybe go to Wikipedia for an overview.

You need to read in the binary file, figure out what all the bits mean, do your transformation, and write out a new binary file. For figuring out the format of various binary files, wotsit is the best resource I've found. They have links to 5 specs for BMP format files.

Related

concatenate files in libffmpeg c++

i'm a bit at loss here. My goal is to merge two video files (which might be of different file formats) and i'm already using libffmpeg for other simple tasks. I thought libffmpeg exposed some kind of function to merge files, but i can't find it.
I found these pages on the documentation that might be relevant: http://ffmpeg.org/doxygen/trunk/structConcatStream.html and http://ffmpeg.org/doxygen/trunk/group__lavf__encoding.html
I'm not sure if this is really relevant though? Can anybody point me in the right direction? Do i need to use FFmpeg muxing and manually joins streams? Is there any example that can explain to me what i should do? thanks!
For those looking for an example, i ended up using
How to use libavformat to concat 2 video files with same codec (re-muxing)?
there's a nice snippet and it works very well
Use ffmpeg to open file 1, start reading frames, converting to target format, and writing to the output file. When there are no more frames, close file 1 (leave output open). Open file 2, start reading frames, converting to target format, and writing to the output file. When there are no more frames, close file 2 and close output.
Merged and formats reconciled.

JPEG header construction

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

Can we load, display and manipulate image's matrix without using any library in c++?

is it possible to do changes to image's matrix without using any library in c++? to load and display image as well?
Sure. Grab a copy of the specification for whatever image format you're interested and write the read/write functions yourself.
Note that to write display functionality without an external library you'll likely need to run your code in kernel mode to get to the frame buffer memory, but that can certainly be done.
Not that you'd necessarily want to do it that way...
Like any typical file, an image file is simply made up of bytes; there is nothing special about an image file.
In my opinion, the most difficult part of reading/writing image files without the use of a library is understanding the file format. Once you understand the format, all you need to do is define appropriate data structures and read the image data into them (for more advanced formats you may have to do some extra work e.g. decompression).
The simplest image format to work with would have to be PPM. It's a pretty bad format but it's nice and easy to read in and write back to a file.
http://netpbm.sourceforge.net/doc/ppm.html
Apart from that, bitmaps are also pretty simple to work with. Like Drew said, just download a copy of the specification and work from there.
As for displaying images, I think you're best off using a library or framework unless you want to see how it's done for the sake of learning.

C++ Importing and Renaming/Resaving an Image

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

Decode JPEG to obtain uncompressed data

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.