Convert bitmap to PNG in-memory in C++ (win32)

Question

Can I convert a bitmap to PNG in memory (i.e. without writing to a file) using only the Platform SDK? (i.e. no libpng, etc.).

I also want to be able to define a tran

Answer 1

LodePNG (GitHub) is a lib-less PNG encoder/decoder.

Answer 2

If you want to only use Windows APIs, WIC is the way to accomplish this, and it supports both Bitmaps and PNGs.

Answer 3

It would probably be better to use a library instead of reinventing the wheel yourself.

Look into freeImage

Answer 4

I read and write PNGs using libpng and it seems to deal with everthing I throw at it (I've used it in unit-tests with things like 257x255 images and they cause no trouble). I believe the API is flexible enough to not be tied to file I/O (or at least you can override its default behaviour e.g see png_set_write_fn in section on customization)

In practice I always use it via the much cleaner boost::gil PNG IO extension, but unfortunately that takes char* filenames and if you dig into it the png_writer and file_mgr classes in its implementation it seem pretty tied to FILE* (although if you were on Linux a version using fmemopen and in-memory buffers could probably be cooked up quite easily).

Answer 5

GDI's (old school, non-plus) has a GetDIBits method that can be asked to output bits using PNG compression (BITMAPINFOHEADER::biCompression == BI_PNG). I wonder if this could be used to create a PNG file? Using GetDIBits to write standard bitmap files is complicated enough - so i suspect this would be even more difficult.

Answer 6

The CImage class (ATL/MFC) supports saving into PNG format. Like the GDI+ solution, it also supports saving to a stream. Here's some code I use to save it to a CByteArray:

CByteArray baPicture;
IStream *pStream = NULL;
if (CreateStreamOnHGlobal(NULL, TRUE, &pStream) == S_OK)
{
    if (image.Save(pStream, Gdiplus::ImageFormatPNG) == S_OK)
    {
    ULARGE_INTEGER ulnSize;
        LARGE_INTEGER lnOffset;
        lnOffset.QuadPart = 0;
        if (pStream->Seek(lnOffset, STREAM_SEEK_END, &ulnSize) == S_OK)
        {
            if (pStream->Seek(lnOffset, STREAM_SEEK_SET, NULL) == S_OK)
            {                       
                baPicture.SetSize(ulnSize.QuadPart);
                ULONG ulBytesRead;
                pStream->Read(baPicture.GetData(), ulnSize.QuadPart, &ulBytesRead);
            }
        }
    }
}
pStream->Release();

I don't know if you'd want to use ATL or MFC, though.