RGB values in images are de-facto sRGB, which is reasonably close to human perception (sRGB gamma curve is close to Munsell lightness curve). In this case appl

RGB values in images are de-facto sRGB, which is reasonably close to human perception (sRGB gamma curve is close to Munsell lightness curve). In this case applying gamma correction to compute the color difference in linear light would make things worse, as it'd model physical properties of the light, rather than human perception.