NHK has been developing 8K Super Hi-Vision (SHV), a member of ultrahigh definition television (UHDTV). This can provide an increased sense of presence and realness to viewers. 8K SHV has system parameters of 7,680×4,320 pixels, 120-Hz frame frequency, and wide-colour gamut. With the addition of an extended image dynamic range feature, it is expected that 8K SHV can be further enhanced to become the true ultimate television system. We first discuss requirements for extended image dynamic range television systems. Then, we propose the essential system parameter values based on the requirements. We introduce the specific parameter of video level corresponding to reference white to address highlights specifically. The proposed system parameters are designed with consideration of compatibility with existing workflows and infrastructure. We conducted an experiment to examine the influence of peak display luminance level on picture production and confirmed that production practices would be substantially changed to fully exploit the display capabilities of the increased luminance levels. We also conducted experiments to determine the required conditions of black level and peak luminance level of displays in various viewing environments.