Convert image into useable byte array in C?

Question

Does anyone know how to open an image, specifically a jpg, to a byte array in C or C++? Any form of help is appreciated.

Thanks!

Answer 1

OpenCV can also do this.

http://www.cs.iit.edu/~agam/cs512/lect-notes/opencv-intro/index.html

search for: "Accessing image elements"

Answer 2

Check out the source code for wxImage in the wxWidgets GUI Framework. You will most likely be interested in the *nix distribution.

Another alternative is the GNU Jpeg library.

Answer 3

Here is how I would do it using GDIPlus Bitmap.LockBits method defined in the header GdiPlusBitmap.h:

    Gdiplus::BitmapData bitmapData;
    Gdiplus::Rect rect(0, 0, bitmap.GetWidth(), bitmap.GetHeight());

    //get the bitmap data
    if(Gdiplus::Ok == bitmap.LockBits(
                        &rect, //A rectangle structure that specifies the portion of the Bitmap to lock.
                        Gdiplus::ImageLockModeRead | Gdiplus::ImageLockModeWrite, //ImageLockMode values that specifies the access level (read/write) for the Bitmap.            
                        bitmap.GetPixelFormat(),// PixelFormat values that specifies the data format of the Bitmap.
                        &bitmapData //BitmapData that will contain the information about the lock operation.
                        ))
    {
         //get the lenght of the bitmap data in bytes
         int len = bitmapData.Height * std::abs(bitmapData.Stride);

         BYTE* buffer = new BYTE[len];
         memcpy(bitmapData.Scan0, buffer, len);//copy it to an array of BYTEs

         //... 

         //cleanup
         pBitmapImageRot.UnlockBits(&bitmapData);       
         delete []buffer;
    }

Answer 4

The ImageMagick library can do this too, although often it provides enough image manipulation functions that you can do many things without needing to convert the image to a byte array and handle it yourself.

Answer 5

You could try the DevIL Image Library I've only used it in relation to OpenGL related things, but it also functions as just a plain image loading library.

Answer 6

I have my students use netpbm to represent images because it comes with a handy C library, but you can also put images into text form, create them by hand, and so on. The nice thing here is that you can convert all sorts of images, not just JPEGs, into PBM format, using command-line tools the Unix way. The djpeg tool is available a number of places including the JPEG Club. Students with relatively little experience can write some fairly sophisticated programs using this format.