Does Draft do its rescale transforms in linear space? e.g. does it assume an sRGB image when it rescales and apply sRGB 2 Lin LUT, rescale and then apply a Lin 2 sRGB? I know some graphics libraries assume they exclusively work in video color space and do that behind the scenes.
Draft doesn’t do any color conversion behind the scenes, so you’ll want to convert to linear color space in your own script.