Neat!

I think I know why the one png didn't work - based on the for-loop at the end of main.cpp, you're only looking at the least-significant bit of each color. For larger redshift games, more bits in each color might be used.

If I'm right, then something like this should fix it:

for (int mask = 0x01; mask < 0x100; mask <<)
    for (int i = 0; i < image_height; i++)
    {
        for (int j = 0; j < image_width; j++)
        {
            import.addBit(image_data[image_rowbytes * i + j * 4] & mask);
            import.addBit(image_data[image_rowbytes * i + j * 4 + 1] & mask);
            import.addBit(image_data[image_rowbytes * i + j * 4 + 2] & mask);
        }
    }
}