This paper proposes a new definition of stereo contrast that suits various types of 3D display devices. An integral type 3D display does not have pre-designed viewing positions, so we can not apply a conventional viewing space analysis approach. We have proposed an image-based stereoscopic viewing space estimation method that uses optical measurement data. We used the method to examine a two-view type 3D display and an integral type 3D display, and showed the effectiveness of the proposed method.