To get much better predictable graphics insertion, with better coordinating of the pixel luminances respectively their coded lumas of primary and secondary graphics elements inserted at different times in a HDR video, the inventor proposes a method of determining in a circuit for processing digital images second lumas of pixels of a secondary graphics image element (216) to be mixed with at least one high dynamic range input image (206), the method or corresponding apparatus comprising the technical elements of:
receiving a high dynamic range image signal (S_im) comprising the at least one high dynamic range input image, characterized in that the method comprises:
- analyzing the high dynamic range image signal to determine a specific range of graphics lumas (R_gra) of the at least one high dynamic range input image, wherein the determining a specific range of graphics lumas comprises determining a lower luma (Y_low) and an upper luma (Y_high);
- specifying the secondary graphics element with at least a brightest subset of its pixel lumas comprised in the specific range of graphics lumas; and
- mixing the secondary graphics image element with the high dynamic range input image.