A method including receiving image data including encoded image data to be decoded to generate decoded image data representing an image and additional data to be read and used to modify the decoded image data. The encoded image data is decoded using an image decoder to generate the decoded image data and the decoded image data is modified based on the additional data to generate modified decoded image data representing the image after modification. Graphics computer program code associated with a programming interface for a graphics processor is derived from at least part of the additional data. The graphics computer program code is for modification of the decoded image data. The decoded image data, along with the graphics computer program code, is passed to the programming interface for modification of the decoded image data.