void reduce_1(T const&,
              image_data_8 & out,
              octree<rgb> /*trees*/[],
              unsigned /*limits*/[],
              std::vector<unsigned> & /*alpha*/)
{
    out.set(0); // only one color!!!
}

void reduce_4(T const& in,
               image_data_8 & out,
               octree<rgb> trees[],
               unsigned limits[],
               unsigned levels,
               std::vector<unsigned> & alpha)
{
    unsigned width = in.width();
    unsigned height = in.height();

    std::vector<unsigned> alphaCount(alpha.size());
    for(unsigned i=0; i<alpha.size(); i++)
    {
        alpha[i] = 0;
        alphaCount[i] = 0;
    }
    for (unsigned y = 0; y < height; ++y)
    {
        mapnik::image_data_32::pixel_type const * row = in.getRow(y);
        mapnik::image_data_8::pixel_type  * row_out = out.getRow(y);
        for (unsigned x = 0; x < width; ++x)
        {
            unsigned val = row[x];
            byte index = 0;
            int idx=-1;
            for(int j=levels-1; j>0; j--)
            {
                if (U2ALPHA(val)>=limits[j] && trees[j].colors()>0)
                {
                    index = idx = trees[j].quantize(val);
                    break;
                }
            }
            if (idx>=0 && idx<(int)alpha.size())
            {
                alpha[idx]+=U2ALPHA(val);
                alphaCount[idx]++;
            }
            if (x%2 == 0)
            {
                index = index<<4;
            }
            row_out[x>>1] |= index;
        }
    }
    for(unsigned i=0; i<alpha.size(); i++)
    {
        if (alphaCount[i]!=0)
        {
            alpha[i] /= alphaCount[i];
        }
    }
}

void save_as_png(T & file, std::vector<rgb> const& palette,
                 image_data_8 const& image,
                 unsigned width,
                 unsigned height,
                 unsigned color_depth,
                 int compression,
                 int strategy,
                 std::vector<unsigned> const&alpha,
                 bool use_miniz)
{
    if (use_miniz) {
        MiniZ::PNGWriter writer(compression);
        // image.width()/height() does not reflect the actual image dimensions; it
        // refers to the quantized scanlines.
        writer.writeIHDR(width, height, color_depth);
        writer.writePLTE(palette);
        writer.writetRNS(alpha);
        writer.writeIDAT(image);
        writer.writeIEND();
        writer.toStream(file);
        return;
    }
    png_voidp error_ptr=0;
    png_structp png_ptr=png_create_write_struct(PNG_LIBPNG_VER_STRING,
                        error_ptr,0, 0);

    if (!png_ptr) return;

    // switch on optimization only if supported
#if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200) && defined(PNG_MMX_CODE_SUPPORTED)
    png_uint_32 mask, flags;
    flags = png_get_asm_flags(png_ptr);
    mask = png_get_asm_flagmask(PNG_SELECT_READ | PNG_SELECT_WRITE);
    png_set_asm_flags(png_ptr, flags | mask);
#endif
    png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE, PNG_FILTER_NONE);
    png_infop info_ptr = png_create_info_struct(png_ptr);
    if (!info_ptr)
    {
        png_destroy_write_struct(&png_ptr,(png_infopp)0);
        return;
    }
    jmp_buf* jmp_context = (jmp_buf*) png_get_error_ptr(png_ptr);
    if (jmp_context)
    {
        png_destroy_write_struct(&png_ptr, &info_ptr);
        return;
    }
    png_set_write_fn (png_ptr, &file, &write_data<T>, &flush_data<T>);

    png_set_compression_level(png_ptr, compression);
    png_set_compression_strategy(png_ptr, strategy);
    png_set_compression_buffer_size(png_ptr, 32768);

    png_set_IHDR(png_ptr, info_ptr,width,height,color_depth,
                 PNG_COLOR_TYPE_PALETTE,PNG_INTERLACE_NONE,
                 PNG_COMPRESSION_TYPE_DEFAULT,PNG_FILTER_TYPE_DEFAULT);

    png_color* pal = const_cast<png_color*>(reinterpret_cast<const png_color*>(&palette[0]));
    png_set_PLTE(png_ptr, info_ptr, pal, palette.size());

    // make transparent lowest indexes, so tRNS is small
    if (alpha.size()>0)
    {
        std::vector<png_byte> trans(alpha.size());
        unsigned alphaSize=0;//truncate to nonopaque values
        for(unsigned i=0; i < alpha.size(); i++)
        {
            trans[i]=alpha[i];
            if (alpha[i]<255)
                alphaSize = i+1;
        }
        if (alphaSize>0)
            png_set_tRNS(png_ptr, info_ptr, (png_bytep)&trans[0], alphaSize, 0);
    }

    png_write_info(png_ptr, info_ptr);
    for (unsigned i=0; i<height; i++)
    {
        png_write_row(png_ptr,(png_bytep)image.getRow(i));
    }

    png_write_end(png_ptr, info_ptr);
    png_destroy_write_struct(&png_ptr, &info_ptr);
}

void reduce_1(T const&, image_data_8 & out, octree<rgb> trees[], unsigned limits[], std::vector<unsigned> & alpha)
{
    out.set(0); // only one color!!!
}