To allow pragmatic insertion of secondary images by an apparatus connected to the final display we invented an image processing apparatus (301, 501) with an output image connection (506) for connection to a display (550), and an input (510) for receiving an input image (IM) and metadata specifying at least one luminance mapping function (F_Lt), which luminance mapping function specifies the relationship between luminances in the input image and a second image with an at least 6 times higher or lower maximum luminance, and comprising a graphics generation unit (502) arranged to determine a secondary image (IMG), and an image composition unit (504) arranged to compose an output image (IMC) on the basis of the pixel colors of the input image and of the secondary image, characterized in that the image processing apparatus comprises a luminance function selection unit (505), which is arranged to output to a metadata output (507) a copy of the at least one luminance mapping function (F_Lt) in case no secondary image colors arc mixed with the input image, and which is arranged to output a predetermined mapping function (F3) in case the output image is not identical to the input image because some pixel colors of the secondary image have been used to change the input image colors.