void WritePNG(const String& filename)
{
	ImageBuffer ib(256, 256);
	ib.SetKind(IMAGE_OPAQUE);
	
	RGBA pal[256];
	for (int i=0; i<256; ++i)
	{
		pal[i] = Color(i,i,i);
	}
	
	int idx = 0;
	for (int y=0; y<256; ++y)
	{
		RGBA* line = ib[y];
		for (int x=0; x<256; ++x)
		{
			*line = pal[idx%256];
			++line;
			++idx;
		}
	}
	
	PNGEncoder png(8);
	png.SetPalette(pal);
	png.SaveFile(filename, ib);
}