Abstract: A computer-implemented method includes executing an initial version of computer game software, the executing step including rendering computer game video images for display; displaying the video images using a head mountable display (HMD); detecting user operation of one or more user controls to perform colour grading adjustments; applying the colour grading adjustments to the video images rendered by the rendering step; and generating colour grading data to be associated with a revised version of the computer game software; in which the executing step and the applying step are performed by different respective data processing apparatus.