Methods and apparatus for determining dynamically a blending ratio for blending features in a computer image generated scene are disclosed. The invention is for use with a computer image generation system which provides a dynamic scene as viewed by the pilot of an aircraft simulator. Such a computer image generator system includes a main data base (62) which contains information representing features of the scene to be presented, a display means (76) and a main computational unit (74) for generating the dynamic visual scene. Apparatus of the present invention includes a control data base (78) which contains selected information related to selected features contained within main data base (62). The selected information contained in control data base (78) includes the spatial coordinates of a control point of the selected feature, and the range at which the feature should be included. Also included in computational unit (74) is a means for determining the location of the central point on a theoretical image plane (61). Means such as CRT (92) which has a pie shaped cut out (98) works in conjunction with a light detector (100) and A/D convertor (106) to determine a proper blending ratio signal. This blending ratio signal is then provided to computational unit (74) to provide the blending of a new feature into the dynamic visual scene. Alternately, a read only memory (ROM) (108) could be used to replace CRT (92), photo detector (100) and A/D convertor (106).