c++ compress byte array

Question

Greetings all,

I load set of images and generate volume data.I save this volume data in a

unsigned char *volume

array.

Now I want to save this array in a file and retrieve.But before saving I want to compress the byte array since the volume data is huge.

Any tips on this?

Thanks in advance.

Answer 1

You will need to use a 3rd party api (as already suggested). If this is C++/CLI you can use zlib.net, but if not then you will need some other library like gzip or lzma.

Here is a link for 7-zip sdk: http://www.7-zip.org/sdk.html

Answer 2

volume in your example is not an array. As for compression, there are books written on the topic. For something quick and easy to use with C++, check out the boost.iostream library, which comes with zlib, gzip, and bzip2 compressors.

To offset my nitpicking, here's an example (changing to char because it's a lot more verbose with unsigned chars)

#include <fstream>
#include <boost/iostreams/filtering_streambuf.hpp>
#include <boost/iostreams/stream.hpp>
#include <boost/iostreams/filter/bzip2.hpp>
#include <boost/iostreams/device/array.hpp>
#include <boost/iostreams/copy.hpp>
namespace io = boost::iostreams;
int main()
{
    const size_t N = 1000000;
    char* volume = new char[N];
    std::fill_n(volume, N, 'a'); // 100,000 letters 'a'

    io::stream< io::array_source > source (volume, N);

    {  
      std::ofstream file("volume.bz2", std::ios::out | std::ios::binary); 
      io::filtering_streambuf<io::output> outStream; 
      outStream.push(io::bzip2_compressor()); 
      outStream.push(file); 
      io::copy(source, outStream); 
     }
    // at this point, volume.bz2 is written and closed. It is 48 bytes long
}

Answer 3

It depends on the type of data. If the images are already compressed (jpeg, png, etc), then it won't compress anymore.

You could use zlib http://www.zlib.net/ for uncompressed images, but I'd suggest to compress each of them with something specialized on images.

Edit:

1) Lossy compression will give much higher compression rates.

2) You mentioned that they are the same size. Are they also similar? A video codec would be the best choise in that case.