Image Number 8 for United States Patent #6084564.
To facilitate determination of a black point on a display unit, a reference brightness region and a comparison brightness region are displayed on the display unit. The former emits at a reference brightness that is used as a reference for determining the black point. The reference brightness is set by inputting a predetermined input value to the display unit. The brightness on the comparison brightness region is compared with the reference brightness. The comparison brightness is changed by increasing and decreasing the input value to the display unit to obtain a critical input value representing the input value wherein an operator can first distinguish the comparison brightness region from the reference brightness region. The two regions are arranged so that the comparison brightness region which is, for example, a star mark is completely surrounded by the reference brightness region, or vice versa.