This will be revisited in Sections 6.2 and 8.4. Each layer has a motion calculation based on the index number applied in step 6. Finally, closely related to motion parallax is optical flow, which is a characterization of the rates at which features move across the retina. The parallax container identified in step 6 has a mousemove event listener attached, which triggers a function to reposition background images of the parallax layers whenever there is mouse movement. Pigeons frequently bob their heads back and forth to obtain stronger depth information than is provided by their pair of eyes. If the rest of the world is stationary, then the result is roughly equivalent to having two side-by-side cameras. Imagine trying to simulate a stereo rig of cameras by snapping one photo and quickly moving the camera sideways to snap another. That’s the key to these CSS powered parallax scenes. Each item is also positioned with scoped custom properties, -x and -y. Each item declares its own level of movement and rotation via -move-x, etc. Even two images, from varying viewpoints within a short amount of time, provide strong depth information. Within architecture, the parallax stands as the apparent displacement of an object that is caused by a distinct change in observational position that provides a new line of sight. The important part there is how we’re making use of -ratio-x and -ratio-y inside the transform. The relative difference in speeds is called parallax and is an important depth cue see Figure 6.6. It makes the background move at a different speed than the foreground content. Thus, motion parallax is a change in position caused by the movement of the viewer. Graham C H, Baker K E, Hecht M, Lloyd V V, 1948 Factors influencing thresholds for monocular movement parallax Journal of Experimental Psychology 38 205223. The term parallax refers to a change in position. If you have ever looked out of the side window of a fast-moving vehicle, you might have noticed that the nearby objects race by much faster than further objects. The parallax effect activates when you start scrolling the page content. Motion parallax is a monocular depth cue arising from the relative velocities of objects moving across the retinae of a moving person. Motion Parallax provides perceptual cues about difference in distance and motion, and is associated with depth perception. Up until now, the depth cues have not exploited motions. Motion parallax: As the perspective changes laterally, closer objects have larger image displacements than further objects.
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