Figure 16.

Luminance maps for estimated surface orientation of stimuli. The upper row shows the luminance maps for a stimulus in Condition C under the (unlikely) assumption that the 3D surface orientation was estimated accurately. The lighting direction was [φ = 30°, θ = 90°] on the left and [φ = 15°, θ = 225°] on the right. The green crosses indicate the true lighting direction. The lower row shows the luminance maps for the same stimuli under the assumption that the assumed shape is a sphere. Now the luminance map is distorted because the assumed surface orientation at each stimulus point is not necessarily correct. The green crosses again represent the true lighting directions. The blue stars represent the lighting directions estimated by the least-squares algorithm described in the Introduction section. Although the assumed shape is incorrect, the lighting-direction estimate is within 20° of the true direction. The red dots represent the settings from each of the four observers when presented these stimuli.