Is it possible to trace back an image say a png image to a jpg? For example an image x.jpg that was converted to x.png. Is there a way of telling that x.png is essentially x.jpg, with the difference being formats?
If l convert img.jpg to img.png is it posssible for me to get back img.jpg?
I intend to check this in C.
As to your first question, the meta-information stored in PNG can tell what the original format or file was. But there is no requirement to store this meta-information in the file.
As to your second question: PNG is a lossless format. So if you decompress a Jpeg image into a bitmap and then encode that bitmap as PNG, you can at least get back from th PNG to the bitmap of the jpeg.
Getting back to the jpeg essentially means re-encoding (compressing) the bitmap, but to arrive at the bitwise identical Jpeg file means using the same compressor settings that were used to create the original Jpeg. As you probably don't know those settings (and it may depend on the compressor code too), I would say "No, you can't get back to the original Jpeg."
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I don't want the error texture of my game engine to rely on an external file, because that file might be deleted, which defeats the purpose of having an error texture. How can I convert an image file into a C-sytle char array that I can read using glTexImage2D?
First, convert your source image file to the 'raw' format (while "remembering" the dimensions of your image in a pair of variables). For this you can use the ImageMagick's convert tool.
The sample for greyscale images conversion is given by this answer. For RGB images either write your own image-to-binary-file converter (since you probably know how to load RGB images for other textures, or use the STB or similar library to load it and then save the image data to a binary file), or (if no automation of this conversion step is needed) just use some GUI tool to save the RAW image.
Then use a tool named bin2h (binary file to C header) which takes a file as an input (your 'raw' file) and outputs a C header with a byte array.
One of such tools can be found at Bin2H#github
Then use the declared array (and a pair of variables with texture dimensions) as an argument to glTexImage2D.
If you have no aversions against 'gimp', gimp has a .h or .c exporter. In that way you have direct access to the dimensions and buffer of your image. Although it is not compressed, so be aware if you want to use a large Image.
I need to get the RGB value reading image. How can i do it in C?
The image format can be png,jpg,bmp or other usual format.
It has to be saved in a text file.
A very easy-to-use image library that can cover the reading and writing of all these formats would be FreeImage. It is primarily a C library, but there are also wrappers for C++, etc.
When you say "saved in a text file", that is pretty atypical for images due to the fact that binary formats are much more compact that storing raw string values for the pixel intensities. Additionally, many formats use compression, which would mean there isn't really a given "value" per-pixel ... instead the data must be decompressed before you can individually assign a value to every pixel. There are some image formats such as PPM that can be stored as ASCII data, but again, that's not necessarily the most efficient way to store a large image.
So for your workflow, you would use a library like FreeImage to read the values out of the image file, and then write back the uncompressed pixel values to a PPM file, or a custom-formatted text file.
I have some images (.bmp, .png, .jpg) in my directory. I want to convert this image to WORD array in order to display this image in LCD in 565 formats (16 bit pixel). How to convert an image to WORD array? Please help. Is is there any utility to just convert the image to binary? or Please provide some code in Windows C/CPP to convert it to binary?
This will depend a whole lot on the exact format of the input image.
Just converting "to words" isn't really expressing what you want to do, which is probably more like "convert bitmap images to an array of RGB565 pixels in row-major format".
You should look at image-processing libraries that allow you to load bitmap images, and read out the value of each pixel.
You can probably just convert directly to RGB565, shouldn't be too hard from any other bitmap format.
Note that there are both indexed and "true color" bitmap formats, and you sound like you need to handle both. If you'er lucky, the library for each format will abstract this away and have e.g. auint32 read_pixel_as_rgb888() function.
Also note that many bitmap image formats focus a lot on compression, which is why just reading in the bits of the file is not nearly enough, you need to de-compress the data according to the format. This is quite complex, which is why pre-written libraries are the only sane choice.
For PNG, look at libpng, for JPEG look for libjpeg. On second thought, these libraries might be a bit too low-level, and maybe you should look at something like SDL_Image instead.
You could try to use CImg to open image files - http://cimg.sourceforge.net/
So what I need is simple: I have IplImage* I want to encode it into JPEG and wrap it with some additional JPEG data if needed (JPEG files contain noty only encoded pixels) and put tha file (not saved onto hard drive) into char* buffer. How to do such thing?
JPEG is a complex format. You can use the IJG jpeg library as a base to work with. However, be warned, it is a mess in itself and has a slight learning curve. It is open source, and you'll typically need to configure its build according to your compiler using a provided makefile (which may not be found with the library code itself)
I'm working on small project in C and at one point, I need to write a picture with the content of an array to a file. This will have to run on an embedded system at some point, so additional libraries are not an option.
The code I have so far works (in a modified version) for RGB, but fails for 8bit Grayscale.
This is a stripped down version of the code so far: http://pastebin.com/U1UYAPuT
As I strongly suspect the header to be broken in some way, my question comes down to: What is a correct header for a BMP file for 8Bit Grayscale?
Your code would be a lot simpler if you ditched BMP and wrote images as PGM files instead. The format is a lot more portable and easy to work with in code. Both formats are uncompressed so data rates would be about the same. The only thing you would lose would be the ability to view the images natively on Windows systems -- whether or not this is a big deal depends on your requirements.
Here are some examples.
EDIT
At the very least, if you write your images in PGM and broken BMP, you can use imagemagick to reliably convert the PGM to a working BMP. Then compare the headers of the working and broken BMP images using a binary diff tool and fix your BMP writer, if required.