Here is how you can use mag's bitmap with Direct2D. You don't need BITMAPINFOHEADER since mag format is the same as DXGI_FORMAT_B8G8R8A8_UNORM:

BOOL MagImageScaling(HWND hwnd, void* srcdata, MAGIMAGEHEADER srcheader, void* destdata, MAGIMAGEHEADER destheader, RECT unclipped, RECT clipped, HRGN dirty)
{
    // note: all this (dc, surface, targte) can be created only once as long as the D3D device isn't reset
    ComPtr<ID2D1DeviceContext> dc;
    HR(d2Device->CreateDeviceContext(D2D1_DEVICE_CONTEXT_OPTIONS_NONE, dc.GetAddressOf()));

    ComPtr<IDXGISurface2> surface;
    HR(swapChain->GetBuffer(0, IID_PPV_ARGS(&surface)));

    ComPtr<ID2D1Bitmap1> target;
    HR(dc->CreateBitmapFromDxgiSurface(surface.Get(), NULL, target.GetAddressOf()));
    dc->SetTarget(target.Get());

    D2D1_BITMAP_PROPERTIES properties = {};
    properties.pixelFormat.alphaMode = D2D1_ALPHA_MODE_PREMULTIPLIED;

    // note: this is ok as srcheader.format (GUID_WICPixelFormat32bppRGBA) is compatible
    properties.pixelFormat.format = DXGI_FORMAT_B8G8R8A8_UNORM; 

    D2D1_SIZE_U size = {};
    size.width = srcheader.width;
    size.height = srcheader.height;

    ComPtr<ID2D1Bitmap> bitmap;
    HR(dc->CreateBitmap(size, properties, bitmap.GetAddressOf()));
    HR(bitmap->CopyFromMemory(NULL, srcdata, srcheader.stride));

    dc->BeginDraw();

    // note: we don't call this because we draw on the whole render target
    //dc->Clear();

    dc->DrawBitmap(bitmap.Get());

    HR(dc->EndDraw());
    HR(swapChain->Present(1, 0));
    return TRUE;
}