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
Related
I've seen a lot of examples of i/o with text files I'm just wondering if you can do the same with other file types like mp3's, jpg's, zip files, etc..?
Will iostream and fstream work for all of these or do I need another library? Do I need a new sdk?
It's all binary data so I'd think it would be that simple. But I've been unpleasently surprised before.
Could I convert all files to text or binary?
It depend on what you mean by "work"
You can think of those files as a book written in Greek.
If you want to just mess with binary representation (display text in Greek on screen) then yes, you can do that.
If you want to actually extract some info: edit video stream, remove voice from audio (actually understand what is written), then you would need to either parse file format yourself (learn Greek) or use some specialized library (hire a translator).
Either way, filestreams are suited to actually access those files data (and many libraries do use them under the hood)
You can work on binary streams by opening them with openmode binary :
ifstream ifs("mydata.mp3", ios_base::binary);
Then you read and write any binary content. However, if you need to generate or modify such content, play a video or display a piture, the you you need to know the inner details of the format you are using. This can be exremely complex, so a library would be recomended. And even with a library, advanced programming skills are required.
Examples of open source libraries: ffmpeg for usual audio/video format, portaudio for audio, CImg for image processing (in C++), libpng for png graphic format, lipjpeg for jpeg. Note that most libraries offer a C api.
Some OS also supports some native file types (example, windows bitmaps).
You can open these files using fstream, but the important thing to note is you must be intricately aware of what is contained within the file in order to process it.
If you just want to open it and spit out junk, then you can definitely just start at the first line of the file and exhaustively push all data into your console.
If you know what the file looks like on the inside, then you can process it just as you would any other file.
There may be specific libraries for processing specific files, but the fstream library will allow you to access any file you'd like.
All files are just bytes. There's nothing stopping you from reading/writing those bytes however you see fit.
The trick is doing something useful with those bytes. You could read the bytes from a .jpg file, for example, but you have to know what those bytes mean, and that's complicated. Usually it's best to use libraries written by people who know about the format in question, and let them deal with that complexity.
I am creating a pdf using libharu in C++ (compiled as a .cgi) that features .png images.
The code is fine, but my pdf's are ridiculously oversized.
Each page features one image of around 30kb and around 4 text characters in libharu's system font. If I open a 20 page output file of 25mb and "print" it to a file in my operating system it becomes 256kb or so with no visible change to the images.
I think the issue is related to libharu because this guy see's it too, here. He is using php so, libharu as a compiled .cgi. (my C++ code is also compiled .cgi, linked to libharu).
Another guy here on stack overflow has also seen size issues with libharu, but his problem does not mention anything to do with .png so it may be unrelated.
Code for reference:
WorkingGraphic = HPDF_LoadPngImageFromMem ( *gPdfPtr,
PngAssets[AssetIndex], //Image data ptr
PngSizes[AssetIndex]); //data length
//Render Appropriate
HPDF_Page_DrawImage (*BlitParams->page,
WorkingGraphic,
BlitParams->OutputRect->X,
BlitParams->OutputRect->Y,
BlitParams->OutputRect->Width,
BlitParams->OutputRect->Height);
Does anyone know how to drive libharu so it creates sensible sized pdf's when you use .png images?
Right I don't know how to remove a question but maybe this info will be useful to others anyway.
I may have had the same issue as this fellow here where I have duplicated this answer.
What I needed to do was enable compression of the .pdf, which I had not done.
Documentation link
C Code:
HPDF_SetCompressionMode (pdf, HPDF_COMP_ALL);
It's because I didn't do enough research to know that .pdf format does not natively support .png, or if it has been updated to do so, libharu still doesn't. So, this option tells libharu to use zlib to zip compress everything it can, including your images.
The implementation is not perfect (you will still see a size difference if you zip your output .pdf) but it is acceptable for my use case.
If you don't need the full-size image in the PDF, you can reduce the image to a thumbnail using GDI+ APIs, equal in size to however big you want the image to appear in the PDF.
Save the scaled PNG to a temporary file, and pass the thumbnail PNG to Haru PDF. This will reduce the size of the PDF file.
The image will be pixellated when the viewer zooms in.
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.
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.
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.