The author of the article seems to assume there is no color conversion (e.g., the resizing of the image is done with sRGB-encoded values rather than converting

The author of the article seems to assume there is no color conversion (e.g., the resizing of the image is done with sRGB-encoded values rather than converting them to linear first). Which is a stupid way to do it but I'd believe most handwritten routines are just that.